first commit

plugin/ai/groq/groq.go

@@ -0,0 +1,110 @@
+package ai
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/sashabaranov/go-openai"
+)
+
+type GroqClient struct {
+	client *openai.Client
+	config GroqConfig
+}
+
+type GroqConfig struct {
+	APIKey      string
+	BaseURL     string
+	DefaultModel string
+}
+
+type CompletionRequest struct {
+	Model       string
+	Prompt      string
+	Temperature float32
+	MaxTokens   int
+}
+
+type CompletionResponse struct {
+	Text          string
+	Model         string
+	PromptTokens  int
+	CompletionTokens int
+	TotalTokens   int
+}
+
+func NewGroqClient(config GroqConfig) *GroqClient {
+	if config.BaseURL == "" {
+		config.BaseURL = "https://api.groq.com/openai/v1"
+	}
+	
+	clientConfig := openai.DefaultConfig(config.APIKey)
+	clientConfig.BaseURL = config.BaseURL
+	
+	return &GroqClient{
+		client: openai.NewClientWithConfig(clientConfig),
+		config: config,
+	}
+}
+
+func (g *GroqClient) TestConnection(ctx context.Context) error {
+	// Test by listing available models
+	_, err := g.client.ListModels(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to connect to Groq API: %w", err)
+	}
+	return nil
+}
+
+func (g *GroqClient) GenerateCompletion(ctx context.Context, req CompletionRequest) (*CompletionResponse, error) {
+	model := req.Model
+	if model == "" {
+		model = g.config.DefaultModel
+	}
+	if model == "" {
+		model = "llama-3.1-8b-instant"
+	}
+
+	chatReq := openai.ChatCompletionRequest{
+		Model: model,
+		Messages: []openai.ChatCompletionMessage{
+			{
+				Role:    openai.ChatMessageRoleUser,
+				Content: req.Prompt,
+			},
+		},
+		Temperature: req.Temperature,
+		MaxTokens:   req.MaxTokens,
+	}
+
+	resp, err := g.client.CreateChatCompletion(ctx, chatReq)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate completion: %w", err)
+	}
+
+	if len(resp.Choices) == 0 {
+		return nil, fmt.Errorf("no completion choices returned")
+	}
+
+	return &CompletionResponse{
+		Text:             resp.Choices[0].Message.Content,
+		Model:            resp.Model,
+		PromptTokens:     resp.Usage.PromptTokens,
+		CompletionTokens: resp.Usage.CompletionTokens,
+		TotalTokens:      resp.Usage.TotalTokens,
+	}, nil
+}
+
+func (g *GroqClient) ListModels(ctx context.Context) ([]string, error) {
+	models, err := g.client.ListModels(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("failed to list models: %w", err)
+	}
+
+	var modelNames []string
+	for _, model := range models.Models {
+		modelNames = append(modelNames, model.ID)
+	}
+	
+	return modelNames, nil
+}

plugin/ai/ollama/ollama.go

@@ -0,0 +1,199 @@
+package ai
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+type OllamaClient struct {
+	httpClient *http.Client
+	config     OllamaConfig
+}
+
+type OllamaConfig struct {
+	Host         string
+	DefaultModel string
+	Timeout      time.Duration
+}
+
+// CompletionRequest is the input for generating completions.
+type CompletionRequest struct {
+	Model       string
+	Prompt      string
+	Temperature float32
+	MaxTokens   int
+}
+
+// CompletionResponse is the output from generating completions.
+type CompletionResponse struct {
+	Text             string
+	Model            string
+	PromptTokens     int
+	CompletionTokens int
+	TotalTokens      int
+}
+
+type OllamaGenerateRequest struct {
+	Model   string `json:"model"`
+	Prompt  string `json:"prompt"`
+	Stream  bool   `json:"stream"`
+	Options map[string]interface{} `json:"options,omitempty"`
+}
+
+type OllamaGenerateResponse struct {
+	Model     string `json:"model"`
+	Response  string `json:"response"`
+	Done      bool   `json:"done"`
+	Context   []int  `json:"context,omitempty"`
+	TotalDuration int64 `json:"total_duration,omitempty"`
+	LoadDuration  int64 `json:"load_duration,omitempty"`
+	PromptEvalCount int `json:"prompt_eval_count,omitempty"`
+	PromptEvalDuration int64 `json:"prompt_eval_duration,omitempty"`
+	EvalCount int `json:"eval_count,omitempty"`
+	EvalDuration int64 `json:"eval_duration,omitempty"`
+}
+
+type OllamaTagsResponse struct {
+	Models []struct {
+		Name    string `json:"name"`
+		Model   string `json:"model"`
+		Size    int64  `json:"size"`
+		Digest  string `json:"digest"`
+	} `json:"models"`
+}
+
+func NewOllamaClient(config OllamaConfig) *OllamaClient {
+	if config.Timeout == 0 {
+		config.Timeout = 120 * time.Second // Increase to 2 minutes for generation
+	}
+	
+	return &OllamaClient{
+		httpClient: &http.Client{
+			Timeout: config.Timeout,
+		},
+		config: config,
+	}
+}
+
+func (o *OllamaClient) TestConnection(ctx context.Context) error {
+	url := fmt.Sprintf("%s/api/tags", o.config.Host)
+	
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return fmt.Errorf("failed to create request: %w", err)
+	}
+	
+	resp, err := o.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("failed to connect to Ollama: %w", err)
+	}
+	defer resp.Body.Close()
+	
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return fmt.Errorf("Ollama returned status %d: %s", resp.StatusCode, string(body))
+	}
+	
+	return nil
+}
+
+func (o *OllamaClient) GenerateCompletion(ctx context.Context, req CompletionRequest) (*CompletionResponse, error) {
+	model := req.Model
+	if model == "" {
+		model = o.config.DefaultModel
+	}
+	if model == "" {
+		model = "llama3"
+	}
+
+	ollamaReq := OllamaGenerateRequest{
+		Model:  model,
+		Prompt: req.Prompt,
+		Stream: false,
+		Options: map[string]interface{}{
+			"temperature": req.Temperature,
+		},
+	}
+
+	if req.MaxTokens > 0 {
+		ollamaReq.Options["num_predict"] = req.MaxTokens
+	}
+
+	jsonData, err := json.Marshal(ollamaReq)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal request: %w", err)
+	}
+
+	url := fmt.Sprintf("%s/api/generate", o.config.Host)
+	httpReq, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewBuffer(jsonData))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+	
+	httpReq.Header.Set("Content-Type", "application/json")
+
+	resp, err := o.httpClient.Do(httpReq)
+	if err != nil {
+		// Check if it's a timeout error
+		if ctx.Err() == context.DeadlineExceeded {
+			return nil, fmt.Errorf("Ollama request timed out after %.0f seconds. Try reducing the max tokens or using a smaller model", o.config.Timeout.Seconds())
+		}
+		return nil, fmt.Errorf("failed to call Ollama API: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("Ollama returned status %d: %s", resp.StatusCode, string(body))
+	}
+
+	var ollamaResp OllamaGenerateResponse
+	if err := json.NewDecoder(resp.Body).Decode(&ollamaResp); err != nil {
+		return nil, fmt.Errorf("failed to decode response: %w", err)
+	}
+
+	return &CompletionResponse{
+		Text:          ollamaResp.Response,
+		Model:         ollamaResp.Model,
+		PromptTokens:  ollamaResp.PromptEvalCount,
+		CompletionTokens: ollamaResp.EvalCount,
+		TotalTokens:   ollamaResp.PromptEvalCount + ollamaResp.EvalCount,
+	}, nil
+}
+
+func (o *OllamaClient) ListModels(ctx context.Context) ([]string, error) {
+	url := fmt.Sprintf("%s/api/tags", o.config.Host)
+	
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+	
+	resp, err := o.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get models: %w", err)
+	}
+	defer resp.Body.Close()
+	
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("Ollama returned status %d: %s", resp.StatusCode, string(body))
+	}
+	
+	var tagsResp OllamaTagsResponse
+	if err := json.NewDecoder(resp.Body).Decode(&tagsResp); err != nil {
+		return nil, fmt.Errorf("failed to decode models response: %w", err)
+	}
+
+	var modelNames []string
+	for _, model := range tagsResp.Models {
+		modelNames = append(modelNames, model.Name)
+	}
+	
+	return modelNames, nil
+}

plugin/cron/README.md

@@ -0,0 +1 @@
+Fork from https://github.com/robfig/cron

plugin/cron/chain.go

@@ -0,0 +1,96 @@
+package cron
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"sync"
+	"time"
+)
+
+// JobWrapper decorates the given Job with some behavior.
+type JobWrapper func(Job) Job
+
+// Chain is a sequence of JobWrappers that decorates submitted jobs with
+// cross-cutting behaviors like logging or synchronization.
+type Chain struct {
+	wrappers []JobWrapper
+}
+
+// NewChain returns a Chain consisting of the given JobWrappers.
+func NewChain(c ...JobWrapper) Chain {
+	return Chain{c}
+}
+
+// Then decorates the given job with all JobWrappers in the chain.
+//
+// This:
+//
+//	NewChain(m1, m2, m3).Then(job)
+//
+// is equivalent to:
+//
+//	m1(m2(m3(job)))
+func (c Chain) Then(j Job) Job {
+	for i := range c.wrappers {
+		j = c.wrappers[len(c.wrappers)-i-1](j)
+	}
+	return j
+}
+
+// Recover panics in wrapped jobs and log them with the provided logger.
+func Recover(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		return FuncJob(func() {
+			defer func() {
+				if r := recover(); r != nil {
+					const size = 64 << 10
+					buf := make([]byte, size)
+					buf = buf[:runtime.Stack(buf, false)]
+					err, ok := r.(error)
+					if !ok {
+						err = errors.New("panic: " + fmt.Sprint(r))
+					}
+					logger.Error(err, "panic", "stack", "...\n"+string(buf))
+				}
+			}()
+			j.Run()
+		})
+	}
+}
+
+// DelayIfStillRunning serializes jobs, delaying subsequent runs until the
+// previous one is complete. Jobs running after a delay of more than a minute
+// have the delay logged at Info.
+func DelayIfStillRunning(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		var mu sync.Mutex
+		return FuncJob(func() {
+			start := time.Now()
+			mu.Lock()
+			defer mu.Unlock()
+			if dur := time.Since(start); dur > time.Minute {
+				logger.Info("delay", "duration", dur)
+			}
+			j.Run()
+		})
+	}
+}
+
+// SkipIfStillRunning skips an invocation of the Job if a previous invocation is
+// still running. It logs skips to the given logger at Info level.
+func SkipIfStillRunning(logger Logger) JobWrapper {
+	return func(j Job) Job {
+		var ch = make(chan struct{}, 1)
+		ch <- struct{}{}
+		return FuncJob(func() {
+			select {
+			case v := <-ch:
+				defer func() { ch <- v }()
+				j.Run()
+			default:
+				logger.Info("skip")
+			}
+		})
+	}
+}

plugin/cron/chain_test.go

@@ -0,0 +1,239 @@
+//nolint:all
+package cron
+
+import (
+	"io"
+	"log"
+	"reflect"
+	"sync"
+	"testing"
+	"time"
+)
+
+func appendingJob(slice *[]int, value int) Job {
+	var m sync.Mutex
+	return FuncJob(func() {
+		m.Lock()
+		*slice = append(*slice, value)
+		m.Unlock()
+	})
+}
+
+func appendingWrapper(slice *[]int, value int) JobWrapper {
+	return func(j Job) Job {
+		return FuncJob(func() {
+			appendingJob(slice, value).Run()
+			j.Run()
+		})
+	}
+}
+
+func TestChain(t *testing.T) {
+	var nums []int
+	var (
+		append1 = appendingWrapper(&nums, 1)
+		append2 = appendingWrapper(&nums, 2)
+		append3 = appendingWrapper(&nums, 3)
+		append4 = appendingJob(&nums, 4)
+	)
+	NewChain(append1, append2, append3).Then(append4).Run()
+	if !reflect.DeepEqual(nums, []int{1, 2, 3, 4}) {
+		t.Error("unexpected order of calls:", nums)
+	}
+}
+
+func TestChainRecover(t *testing.T) {
+	panickingJob := FuncJob(func() {
+		panic("panickingJob panics")
+	})
+
+	t.Run("panic exits job by default", func(*testing.T) {
+		defer func() {
+			if err := recover(); err == nil {
+				t.Errorf("panic expected, but none received")
+			}
+		}()
+		NewChain().Then(panickingJob).
+			Run()
+	})
+
+	t.Run("Recovering JobWrapper recovers", func(*testing.T) {
+		NewChain(Recover(PrintfLogger(log.New(io.Discard, "", 0)))).
+			Then(panickingJob).
+			Run()
+	})
+
+	t.Run("composed with the *IfStillRunning wrappers", func(*testing.T) {
+		NewChain(Recover(PrintfLogger(log.New(io.Discard, "", 0)))).
+			Then(panickingJob).
+			Run()
+	})
+}
+
+type countJob struct {
+	m       sync.Mutex
+	started int
+	done    int
+	delay   time.Duration
+}
+
+func (j *countJob) Run() {
+	j.m.Lock()
+	j.started++
+	j.m.Unlock()
+	time.Sleep(j.delay)
+	j.m.Lock()
+	j.done++
+	j.m.Unlock()
+}
+
+func (j *countJob) Started() int {
+	defer j.m.Unlock()
+	j.m.Lock()
+	return j.started
+}
+
+func (j *countJob) Done() int {
+	defer j.m.Unlock()
+	j.m.Lock()
+	return j.done
+}
+
+func TestChainDelayIfStillRunning(t *testing.T) {
+	t.Run("runs immediately", func(*testing.T) {
+		var j countJob
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go wrappedJob.Run()
+		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
+		if c := j.Done(); c != 1 {
+			t.Errorf("expected job run once, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run immediate if first done", func(*testing.T) {
+		var j countJob
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
+		if c := j.Done(); c != 2 {
+			t.Errorf("expected job run twice, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run delayed if first not done", func(*testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(DelayIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+
+		// After 5ms, the first job is still in progress, and the second job was
+		// run but should be waiting for it to finish.
+		time.Sleep(5 * time.Millisecond)
+		started, done := j.Started(), j.Done()
+		if started != 1 || done != 0 {
+			t.Error("expected first job started, but not finished, got", started, done)
+		}
+
+		// Verify that the second job completes.
+		time.Sleep(25 * time.Millisecond)
+		started, done = j.Started(), j.Done()
+		if started != 2 || done != 2 {
+			t.Error("expected both jobs done, got", started, done)
+		}
+	})
+}
+
+func TestChainSkipIfStillRunning(t *testing.T) {
+	t.Run("runs immediately", func(*testing.T) {
+		var j countJob
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go wrappedJob.Run()
+		time.Sleep(2 * time.Millisecond) // Give the job 2ms to complete.
+		if c := j.Done(); c != 1 {
+			t.Errorf("expected job run once, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run immediate if first done", func(*testing.T) {
+		var j countJob
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+		time.Sleep(3 * time.Millisecond) // Give both jobs 3ms to complete.
+		if c := j.Done(); c != 2 {
+			t.Errorf("expected job run twice, immediately, got %d", c)
+		}
+	})
+
+	t.Run("second run skipped if first not done", func(*testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		go func() {
+			go wrappedJob.Run()
+			time.Sleep(time.Millisecond)
+			go wrappedJob.Run()
+		}()
+
+		// After 5ms, the first job is still in progress, and the second job was
+		// already skipped.
+		time.Sleep(5 * time.Millisecond)
+		started, done := j.Started(), j.Done()
+		if started != 1 || done != 0 {
+			t.Error("expected first job started, but not finished, got", started, done)
+		}
+
+		// Verify that the first job completes and second does not run.
+		time.Sleep(25 * time.Millisecond)
+		started, done = j.Started(), j.Done()
+		if started != 1 || done != 1 {
+			t.Error("expected second job skipped, got", started, done)
+		}
+	})
+
+	t.Run("skip 10 jobs on rapid fire", func(*testing.T) {
+		var j countJob
+		j.delay = 10 * time.Millisecond
+		wrappedJob := NewChain(SkipIfStillRunning(DiscardLogger)).Then(&j)
+		for i := 0; i < 11; i++ {
+			go wrappedJob.Run()
+		}
+		time.Sleep(200 * time.Millisecond)
+		done := j.Done()
+		if done != 1 {
+			t.Error("expected 1 jobs executed, 10 jobs dropped, got", done)
+		}
+	})
+
+	t.Run("different jobs independent", func(*testing.T) {
+		var j1, j2 countJob
+		j1.delay = 10 * time.Millisecond
+		j2.delay = 10 * time.Millisecond
+		chain := NewChain(SkipIfStillRunning(DiscardLogger))
+		wrappedJob1 := chain.Then(&j1)
+		wrappedJob2 := chain.Then(&j2)
+		for i := 0; i < 11; i++ {
+			go wrappedJob1.Run()
+			go wrappedJob2.Run()
+		}
+		time.Sleep(100 * time.Millisecond)
+		var (
+			done1 = j1.Done()
+			done2 = j2.Done()
+		)
+		if done1 != 1 || done2 != 1 {
+			t.Error("expected both jobs executed once, got", done1, "and", done2)
+		}
+	})
+}

plugin/cron/constantdelay.go

@@ -0,0 +1,27 @@
+package cron
+
+import "time"
+
+// ConstantDelaySchedule represents a simple recurring duty cycle, e.g. "Every 5 minutes".
+// It does not support jobs more frequent than once a second.
+type ConstantDelaySchedule struct {
+	Delay time.Duration
+}
+
+// Every returns a crontab Schedule that activates once every duration.
+// Delays of less than a second are not supported (will round up to 1 second).
+// Any fields less than a Second are truncated.
+func Every(duration time.Duration) ConstantDelaySchedule {
+	if duration < time.Second {
+		duration = time.Second
+	}
+	return ConstantDelaySchedule{
+		Delay: duration - time.Duration(duration.Nanoseconds())%time.Second,
+	}
+}
+
+// Next returns the next time this should be run.
+// This rounds so that the next activation time will be on the second.
+func (schedule ConstantDelaySchedule) Next(t time.Time) time.Time {
+	return t.Add(schedule.Delay - time.Duration(t.Nanosecond())*time.Nanosecond)
+}

plugin/cron/constantdelay_test.go

@@ -0,0 +1,55 @@
+//nolint:all
+package cron
+
+import (
+	"testing"
+	"time"
+)
+
+func TestConstantDelayNext(t *testing.T) {
+	tests := []struct {
+		time     string
+		delay    time.Duration
+		expected string
+	}{
+		// Simple cases
+		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+		{"Mon Jul 9 14:59 2012", 15 * time.Minute, "Mon Jul 9 15:14 2012"},
+		{"Mon Jul 9 14:59:59 2012", 15 * time.Minute, "Mon Jul 9 15:14:59 2012"},
+
+		// Wrap around hours
+		{"Mon Jul 9 15:45 2012", 35 * time.Minute, "Mon Jul 9 16:20 2012"},
+
+		// Wrap around days
+		{"Mon Jul 9 23:46 2012", 14 * time.Minute, "Tue Jul 10 00:00 2012"},
+		{"Mon Jul 9 23:45 2012", 35 * time.Minute, "Tue Jul 10 00:20 2012"},
+		{"Mon Jul 9 23:35:51 2012", 44*time.Minute + 24*time.Second, "Tue Jul 10 00:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", 25*time.Hour + 44*time.Minute + 24*time.Second, "Thu Jul 11 01:20:15 2012"},
+
+		// Wrap around months
+		{"Mon Jul 9 23:35 2012", 91*24*time.Hour + 25*time.Minute, "Thu Oct 9 00:00 2012"},
+
+		// Wrap around minute, hour, day, month, and year
+		{"Mon Dec 31 23:59:45 2012", 15 * time.Second, "Tue Jan 1 00:00:00 2013"},
+
+		// Round to nearest second on the delay
+		{"Mon Jul 9 14:45 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+
+		// Round up to 1 second if the duration is less.
+		{"Mon Jul 9 14:45:00 2012", 15 * time.Millisecond, "Mon Jul 9 14:45:01 2012"},
+
+		// Round to nearest second when calculating the next time.
+		{"Mon Jul 9 14:45:00.005 2012", 15 * time.Minute, "Mon Jul 9 15:00 2012"},
+
+		// Round to nearest second for both.
+		{"Mon Jul 9 14:45:00.005 2012", 15*time.Minute + 50*time.Nanosecond, "Mon Jul 9 15:00 2012"},
+	}
+
+	for _, c := range tests {
+		actual := Every(c.delay).Next(getTime(c.time))
+		expected := getTime(c.expected)
+		if actual != expected {
+			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.delay, expected, actual)
+		}
+	}
+}

plugin/cron/cron.go

@@ -0,0 +1,353 @@
+package cron
+
+import (
+	"context"
+	"sort"
+	"sync"
+	"time"
+)
+
+// Cron keeps track of any number of entries, invoking the associated func as
+// specified by the schedule. It may be started, stopped, and the entries may
+// be inspected while running.
+type Cron struct {
+	entries   []*Entry
+	chain     Chain
+	stop      chan struct{}
+	add       chan *Entry
+	remove    chan EntryID
+	snapshot  chan chan []Entry
+	running   bool
+	logger    Logger
+	runningMu sync.Mutex
+	location  *time.Location
+	parser    ScheduleParser
+	nextID    EntryID
+	jobWaiter sync.WaitGroup
+}
+
+// ScheduleParser is an interface for schedule spec parsers that return a Schedule.
+type ScheduleParser interface {
+	Parse(spec string) (Schedule, error)
+}
+
+// Job is an interface for submitted cron jobs.
+type Job interface {
+	Run()
+}
+
+// Schedule describes a job's duty cycle.
+type Schedule interface {
+	// Next returns the next activation time, later than the given time.
+	// Next is invoked initially, and then each time the job is run.
+	Next(time.Time) time.Time
+}
+
+// EntryID identifies an entry within a Cron instance.
+type EntryID int
+
+// Entry consists of a schedule and the func to execute on that schedule.
+type Entry struct {
+	// ID is the cron-assigned ID of this entry, which may be used to look up a
+	// snapshot or remove it.
+	ID EntryID
+
+	// Schedule on which this job should be run.
+	Schedule Schedule
+
+	// Next time the job will run, or the zero time if Cron has not been
+	// started or this entry's schedule is unsatisfiable
+	Next time.Time
+
+	// Prev is the last time this job was run, or the zero time if never.
+	Prev time.Time
+
+	// WrappedJob is the thing to run when the Schedule is activated.
+	WrappedJob Job
+
+	// Job is the thing that was submitted to cron.
+	// It is kept around so that user code that needs to get at the job later,
+	// e.g. via Entries() can do so.
+	Job Job
+}
+
+// Valid returns true if this is not the zero entry.
+func (e Entry) Valid() bool { return e.ID != 0 }
+
+// byTime is a wrapper for sorting the entry array by time
+// (with zero time at the end).
+type byTime []*Entry
+
+func (s byTime) Len() int      { return len(s) }
+func (s byTime) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s byTime) Less(i, j int) bool {
+	// Two zero times should return false.
+	// Otherwise, zero is "greater" than any other time.
+	// (To sort it at the end of the list.)
+	if s[i].Next.IsZero() {
+		return false
+	}
+	if s[j].Next.IsZero() {
+		return true
+	}
+	return s[i].Next.Before(s[j].Next)
+}
+
+// New returns a new Cron job runner, modified by the given options.
+//
+// Available Settings
+//
+//	Time Zone
+//	  Description: The time zone in which schedules are interpreted
+//	  Default:     time.Local
+//
+//	Parser
+//	  Description: Parser converts cron spec strings into cron.Schedules.
+//	  Default:     Accepts this spec: https://en.wikipedia.org/wiki/Cron
+//
+//	Chain
+//	  Description: Wrap submitted jobs to customize behavior.
+//	  Default:     A chain that recovers panics and logs them to stderr.
+//
+// See "cron.With*" to modify the default behavior.
+func New(opts ...Option) *Cron {
+	c := &Cron{
+		entries:   nil,
+		chain:     NewChain(),
+		add:       make(chan *Entry),
+		stop:      make(chan struct{}),
+		snapshot:  make(chan chan []Entry),
+		remove:    make(chan EntryID),
+		running:   false,
+		runningMu: sync.Mutex{},
+		logger:    DefaultLogger,
+		location:  time.Local,
+		parser:    standardParser,
+	}
+	for _, opt := range opts {
+		opt(c)
+	}
+	return c
+}
+
+// FuncJob is a wrapper that turns a func() into a cron.Job.
+type FuncJob func()
+
+func (f FuncJob) Run() { f() }
+
+// AddFunc adds a func to the Cron to be run on the given schedule.
+// The spec is parsed using the time zone of this Cron instance as the default.
+// An opaque ID is returned that can be used to later remove it.
+func (c *Cron) AddFunc(spec string, cmd func()) (EntryID, error) {
+	return c.AddJob(spec, FuncJob(cmd))
+}
+
+// AddJob adds a Job to the Cron to be run on the given schedule.
+// The spec is parsed using the time zone of this Cron instance as the default.
+// An opaque ID is returned that can be used to later remove it.
+func (c *Cron) AddJob(spec string, cmd Job) (EntryID, error) {
+	schedule, err := c.parser.Parse(spec)
+	if err != nil {
+		return 0, err
+	}
+	return c.Schedule(schedule, cmd), nil
+}
+
+// Schedule adds a Job to the Cron to be run on the given schedule.
+// The job is wrapped with the configured Chain.
+func (c *Cron) Schedule(schedule Schedule, cmd Job) EntryID {
+	c.runningMu.Lock()
+	defer c.runningMu.Unlock()
+	c.nextID++
+	entry := &Entry{
+		ID:         c.nextID,
+		Schedule:   schedule,
+		WrappedJob: c.chain.Then(cmd),
+		Job:        cmd,
+	}
+	if !c.running {
+		c.entries = append(c.entries, entry)
+	} else {
+		c.add <- entry
+	}
+	return entry.ID
+}
+
+// Entries returns a snapshot of the cron entries.
+func (c *Cron) Entries() []Entry {
+	c.runningMu.Lock()
+	defer c.runningMu.Unlock()
+	if c.running {
+		replyChan := make(chan []Entry, 1)
+		c.snapshot <- replyChan
+		return <-replyChan
+	}
+	return c.entrySnapshot()
+}
+
+// Location gets the time zone location.
+func (c *Cron) Location() *time.Location {
+	return c.location
+}
+
+// Entry returns a snapshot of the given entry, or nil if it couldn't be found.
+func (c *Cron) Entry(id EntryID) Entry {
+	for _, entry := range c.Entries() {
+		if id == entry.ID {
+			return entry
+		}
+	}
+	return Entry{}
+}
+
+// Remove an entry from being run in the future.
+func (c *Cron) Remove(id EntryID) {
+	c.runningMu.Lock()
+	defer c.runningMu.Unlock()
+	if c.running {
+		c.remove <- id
+	} else {
+		c.removeEntry(id)
+	}
+}
+
+// Start the cron scheduler in its own goroutine, or no-op if already started.
+func (c *Cron) Start() {
+	c.runningMu.Lock()
+	defer c.runningMu.Unlock()
+	if c.running {
+		return
+	}
+	c.running = true
+	go c.runScheduler()
+}
+
+// Run the cron scheduler, or no-op if already running.
+func (c *Cron) Run() {
+	c.runningMu.Lock()
+	if c.running {
+		c.runningMu.Unlock()
+		return
+	}
+	c.running = true
+	c.runningMu.Unlock()
+	c.runScheduler()
+}
+
+// runScheduler runs the scheduler.. this is private just due to the need to synchronize
+// access to the 'running' state variable.
+func (c *Cron) runScheduler() {
+	c.logger.Info("start")
+
+	// Figure out the next activation times for each entry.
+	now := c.now()
+	for _, entry := range c.entries {
+		entry.Next = entry.Schedule.Next(now)
+		c.logger.Info("schedule", "now", now, "entry", entry.ID, "next", entry.Next)
+	}
+
+	for {
+		// Determine the next entry to run.
+		sort.Sort(byTime(c.entries))
+
+		var timer *time.Timer
+		if len(c.entries) == 0 || c.entries[0].Next.IsZero() {
+			// If there are no entries yet, just sleep - it still handles new entries
+			// and stop requests.
+			timer = time.NewTimer(100000 * time.Hour)
+		} else {
+			timer = time.NewTimer(c.entries[0].Next.Sub(now))
+		}
+
+		for {
+			select {
+			case now = <-timer.C:
+				now = now.In(c.location)
+				c.logger.Info("wake", "now", now)
+
+				// Run every entry whose next time was less than now
+				for _, e := range c.entries {
+					if e.Next.After(now) || e.Next.IsZero() {
+						break
+					}
+					c.startJob(e.WrappedJob)
+					e.Prev = e.Next
+					e.Next = e.Schedule.Next(now)
+					c.logger.Info("run", "now", now, "entry", e.ID, "next", e.Next)
+				}
+
+			case newEntry := <-c.add:
+				timer.Stop()
+				now = c.now()
+				newEntry.Next = newEntry.Schedule.Next(now)
+				c.entries = append(c.entries, newEntry)
+				c.logger.Info("added", "now", now, "entry", newEntry.ID, "next", newEntry.Next)
+
+			case replyChan := <-c.snapshot:
+				replyChan <- c.entrySnapshot()
+				continue
+
+			case <-c.stop:
+				timer.Stop()
+				c.logger.Info("stop")
+				return
+
+			case id := <-c.remove:
+				timer.Stop()
+				now = c.now()
+				c.removeEntry(id)
+				c.logger.Info("removed", "entry", id)
+			}
+
+			break
+		}
+	}
+}
+
+// startJob runs the given job in a new goroutine.
+func (c *Cron) startJob(j Job) {
+	c.jobWaiter.Go(func() {
+		j.Run()
+	})
+}
+
+// now returns current time in c location.
+func (c *Cron) now() time.Time {
+	return time.Now().In(c.location)
+}
+
+// Stop stops the cron scheduler if it is running; otherwise it does nothing.
+// A context is returned so the caller can wait for running jobs to complete.
+func (c *Cron) Stop() context.Context {
+	c.runningMu.Lock()
+	defer c.runningMu.Unlock()
+	if c.running {
+		c.stop <- struct{}{}
+		c.running = false
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		c.jobWaiter.Wait()
+		cancel()
+	}()
+	return ctx
+}
+
+// entrySnapshot returns a copy of the current cron entry list.
+func (c *Cron) entrySnapshot() []Entry {
+	var entries = make([]Entry, len(c.entries))
+	for i, e := range c.entries {
+		entries[i] = *e
+	}
+	return entries
+}
+
+func (c *Cron) removeEntry(id EntryID) {
+	var entries []*Entry
+	for _, e := range c.entries {
+		if e.ID != id {
+			entries = append(entries, e)
+		}
+	}
+	c.entries = entries
+}

plugin/cron/cron_test.go

@@ -0,0 +1,702 @@
+//nolint:all
+package cron
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// Many tests schedule a job for every second, and then wait at most a second
+// for it to run.  This amount is just slightly larger than 1 second to
+// compensate for a few milliseconds of runtime.
+const OneSecond = 1*time.Second + 50*time.Millisecond
+
+type syncWriter struct {
+	wr bytes.Buffer
+	m  sync.Mutex
+}
+
+func (sw *syncWriter) Write(data []byte) (n int, err error) {
+	sw.m.Lock()
+	n, err = sw.wr.Write(data)
+	sw.m.Unlock()
+	return
+}
+
+func (sw *syncWriter) String() string {
+	sw.m.Lock()
+	defer sw.m.Unlock()
+	return sw.wr.String()
+}
+
+func newBufLogger(sw *syncWriter) Logger {
+	return PrintfLogger(log.New(sw, "", log.LstdFlags))
+}
+
+func TestFuncPanicRecovery(t *testing.T) {
+	var buf syncWriter
+	cron := New(WithParser(secondParser),
+		WithChain(Recover(newBufLogger(&buf))))
+	cron.Start()
+	defer cron.Stop()
+	cron.AddFunc("* * * * * ?", func() {
+		panic("YOLO")
+	})
+
+	select {
+	case <-time.After(OneSecond):
+		if !strings.Contains(buf.String(), "YOLO") {
+			t.Error("expected a panic to be logged, got none")
+		}
+		return
+	}
+}
+
+type DummyJob struct{}
+
+func (DummyJob) Run() {
+	panic("YOLO")
+}
+
+func TestJobPanicRecovery(t *testing.T) {
+	var job DummyJob
+
+	var buf syncWriter
+	cron := New(WithParser(secondParser),
+		WithChain(Recover(newBufLogger(&buf))))
+	cron.Start()
+	defer cron.Stop()
+	cron.AddJob("* * * * * ?", job)
+
+	select {
+	case <-time.After(OneSecond):
+		if !strings.Contains(buf.String(), "YOLO") {
+			t.Error("expected a panic to be logged, got none")
+		}
+		return
+	}
+}
+
+// Start and stop cron with no entries.
+func TestNoEntries(t *testing.T) {
+	cron := newWithSeconds()
+	cron.Start()
+
+	select {
+	case <-time.After(OneSecond):
+		t.Fatal("expected cron will be stopped immediately")
+	case <-stop(cron):
+	}
+}
+
+// Start, stop, then add an entry. Verify entry doesn't run.
+func TestStopCausesJobsToNotRun(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.Start()
+	cron.Stop()
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+
+	select {
+	case <-time.After(OneSecond):
+		// No job ran!
+	case <-wait(wg):
+		t.Fatal("expected stopped cron does not run any job")
+	}
+}
+
+// Add a job, start cron, expect it runs.
+func TestAddBeforeRunning(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+	cron.Start()
+	defer cron.Stop()
+
+	// Give cron 2 seconds to run our job (which is always activated).
+	select {
+	case <-time.After(OneSecond):
+		t.Fatal("expected job runs")
+	case <-wait(wg):
+	}
+}
+
+// Start cron, add a job, expect it runs.
+func TestAddWhileRunning(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.Start()
+	defer cron.Stop()
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+
+	select {
+	case <-time.After(OneSecond):
+		t.Fatal("expected job runs")
+	case <-wait(wg):
+	}
+}
+
+// Test for #34. Adding a job after calling start results in multiple job invocations
+func TestAddWhileRunningWithDelay(t *testing.T) {
+	cron := newWithSeconds()
+	cron.Start()
+	defer cron.Stop()
+	time.Sleep(5 * time.Second)
+	var calls int64
+	cron.AddFunc("* * * * * *", func() { atomic.AddInt64(&calls, 1) })
+
+	<-time.After(OneSecond)
+	if atomic.LoadInt64(&calls) != 1 {
+		t.Errorf("called %d times, expected 1\n", calls)
+	}
+}
+
+// Add a job, remove a job, start cron, expect nothing runs.
+func TestRemoveBeforeRunning(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	id, _ := cron.AddFunc("* * * * * ?", func() { wg.Done() })
+	cron.Remove(id)
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond):
+		// Success, shouldn't run
+	case <-wait(wg):
+		t.FailNow()
+	}
+}
+
+// Start cron, add a job, remove it, expect it doesn't run.
+func TestRemoveWhileRunning(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.Start()
+	defer cron.Stop()
+	id, _ := cron.AddFunc("* * * * * ?", func() { wg.Done() })
+	cron.Remove(id)
+
+	select {
+	case <-time.After(OneSecond):
+	case <-wait(wg):
+		t.FailNow()
+	}
+}
+
+// Test timing with Entries.
+func TestSnapshotEntries(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := New()
+	cron.AddFunc("@every 2s", func() { wg.Done() })
+	cron.Start()
+	defer cron.Stop()
+
+	// Cron should fire in 2 seconds. After 1 second, call Entries.
+	select {
+	case <-time.After(OneSecond):
+		cron.Entries()
+	}
+
+	// Even though Entries was called, the cron should fire at the 2 second mark.
+	select {
+	case <-time.After(OneSecond):
+		t.Error("expected job runs at 2 second mark")
+	case <-wait(wg):
+	}
+}
+
+// Test that the entries are correctly sorted.
+// Add a bunch of long-in-the-future entries, and an immediate entry, and ensure
+// that the immediate entry runs immediately.
+// Also: Test that multiple jobs run in the same instant.
+func TestMultipleEntries(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(2)
+
+	cron := newWithSeconds()
+	cron.AddFunc("0 0 0 1 1 ?", func() {})
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+	id1, _ := cron.AddFunc("* * * * * ?", func() { t.Fatal() })
+	id2, _ := cron.AddFunc("* * * * * ?", func() { t.Fatal() })
+	cron.AddFunc("0 0 0 31 12 ?", func() {})
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+
+	cron.Remove(id1)
+	cron.Start()
+	cron.Remove(id2)
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond):
+		t.Error("expected job run in proper order")
+	case <-wait(wg):
+	}
+}
+
+// Test running the same job twice.
+func TestRunningJobTwice(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(2)
+
+	cron := newWithSeconds()
+	cron.AddFunc("0 0 0 1 1 ?", func() {})
+	cron.AddFunc("0 0 0 31 12 ?", func() {})
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(2 * OneSecond):
+		t.Error("expected job fires 2 times")
+	case <-wait(wg):
+	}
+}
+
+func TestRunningMultipleSchedules(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(2)
+
+	cron := newWithSeconds()
+	cron.AddFunc("0 0 0 1 1 ?", func() {})
+	cron.AddFunc("0 0 0 31 12 ?", func() {})
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+	cron.Schedule(Every(time.Minute), FuncJob(func() {}))
+	cron.Schedule(Every(time.Second), FuncJob(func() { wg.Done() }))
+	cron.Schedule(Every(time.Hour), FuncJob(func() {}))
+
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(2 * OneSecond):
+		t.Error("expected job fires 2 times")
+	case <-wait(wg):
+	}
+}
+
+// Test that the cron is run in the local time zone (as opposed to UTC).
+func TestLocalTimezone(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(2)
+
+	now := time.Now()
+	// FIX: Issue #205
+	// This calculation doesn't work in seconds 58 or 59.
+	// Take the easy way out and sleep.
+	if now.Second() >= 58 {
+		time.Sleep(2 * time.Second)
+		now = time.Now()
+	}
+	spec := fmt.Sprintf("%d,%d %d %d %d %d ?",
+		now.Second()+1, now.Second()+2, now.Minute(), now.Hour(), now.Day(), now.Month())
+
+	cron := newWithSeconds()
+	cron.AddFunc(spec, func() { wg.Done() })
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond * 2):
+		t.Error("expected job fires 2 times")
+	case <-wait(wg):
+	}
+}
+
+// Test that the cron is run in the given time zone (as opposed to local).
+func TestNonLocalTimezone(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(2)
+
+	loc, err := time.LoadLocation("Atlantic/Cape_Verde")
+	if err != nil {
+		fmt.Printf("Failed to load time zone Atlantic/Cape_Verde: %+v", err)
+		t.Fail()
+	}
+
+	now := time.Now().In(loc)
+	// FIX: Issue #205
+	// This calculation doesn't work in seconds 58 or 59.
+	// Take the easy way out and sleep.
+	if now.Second() >= 58 {
+		time.Sleep(2 * time.Second)
+		now = time.Now().In(loc)
+	}
+	spec := fmt.Sprintf("%d,%d %d %d %d %d ?",
+		now.Second()+1, now.Second()+2, now.Minute(), now.Hour(), now.Day(), now.Month())
+
+	cron := New(WithLocation(loc), WithParser(secondParser))
+	cron.AddFunc(spec, func() { wg.Done() })
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond * 2):
+		t.Error("expected job fires 2 times")
+	case <-wait(wg):
+	}
+}
+
+// Test that calling stop before start silently returns without
+// blocking the stop channel.
+func TestStopWithoutStart(t *testing.T) {
+	cron := New()
+	cron.Stop()
+}
+
+type testJob struct {
+	wg   *sync.WaitGroup
+	name string
+}
+
+func (t testJob) Run() {
+	t.wg.Done()
+}
+
+// Test that adding an invalid job spec returns an error
+func TestInvalidJobSpec(t *testing.T) {
+	cron := New()
+	_, err := cron.AddJob("this will not parse", nil)
+	if err == nil {
+		t.Errorf("expected an error with invalid spec, got nil")
+	}
+}
+
+// Test blocking run method behaves as Start()
+func TestBlockingRun(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.AddFunc("* * * * * ?", func() { wg.Done() })
+
+	var unblockChan = make(chan struct{})
+
+	go func() {
+		cron.Run()
+		close(unblockChan)
+	}()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond):
+		t.Error("expected job fires")
+	case <-unblockChan:
+		t.Error("expected that Run() blocks")
+	case <-wait(wg):
+	}
+}
+
+// Test that double-running is a no-op
+func TestStartNoop(t *testing.T) {
+	var tickChan = make(chan struct{}, 2)
+
+	cron := newWithSeconds()
+	cron.AddFunc("* * * * * ?", func() {
+		tickChan <- struct{}{}
+	})
+
+	cron.Start()
+	defer cron.Stop()
+
+	// Wait for the first firing to ensure the runner is going
+	<-tickChan
+
+	cron.Start()
+
+	<-tickChan
+
+	// Fail if this job fires again in a short period, indicating a double-run
+	select {
+	case <-time.After(time.Millisecond):
+	case <-tickChan:
+		t.Error("expected job fires exactly twice")
+	}
+}
+
+// Simple test using Runnables.
+func TestJob(t *testing.T) {
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+
+	cron := newWithSeconds()
+	cron.AddJob("0 0 0 30 Feb ?", testJob{wg, "job0"})
+	cron.AddJob("0 0 0 1 1 ?", testJob{wg, "job1"})
+	job2, _ := cron.AddJob("* * * * * ?", testJob{wg, "job2"})
+	cron.AddJob("1 0 0 1 1 ?", testJob{wg, "job3"})
+	cron.Schedule(Every(5*time.Second+5*time.Nanosecond), testJob{wg, "job4"})
+	job5 := cron.Schedule(Every(5*time.Minute), testJob{wg, "job5"})
+
+	// Test getting an Entry pre-Start.
+	if actualName := cron.Entry(job2).Job.(testJob).name; actualName != "job2" {
+		t.Error("wrong job retrieved:", actualName)
+	}
+	if actualName := cron.Entry(job5).Job.(testJob).name; actualName != "job5" {
+		t.Error("wrong job retrieved:", actualName)
+	}
+
+	cron.Start()
+	defer cron.Stop()
+
+	select {
+	case <-time.After(OneSecond):
+		t.FailNow()
+	case <-wait(wg):
+	}
+
+	// Ensure the entries are in the right order.
+	expecteds := []string{"job2", "job4", "job5", "job1", "job3", "job0"}
+
+	var actuals []string
+	for _, entry := range cron.Entries() {
+		actuals = append(actuals, entry.Job.(testJob).name)
+	}
+
+	for i, expected := range expecteds {
+		if actuals[i] != expected {
+			t.Fatalf("Jobs not in the right order.  (expected) %s != %s (actual)", expecteds, actuals)
+		}
+	}
+
+	// Test getting Entries.
+	if actualName := cron.Entry(job2).Job.(testJob).name; actualName != "job2" {
+		t.Error("wrong job retrieved:", actualName)
+	}
+	if actualName := cron.Entry(job5).Job.(testJob).name; actualName != "job5" {
+		t.Error("wrong job retrieved:", actualName)
+	}
+}
+
+// Issue #206
+// Ensure that the next run of a job after removing an entry is accurate.
+func TestScheduleAfterRemoval(t *testing.T) {
+	var wg1 sync.WaitGroup
+	var wg2 sync.WaitGroup
+	wg1.Add(1)
+	wg2.Add(1)
+
+	// The first time this job is run, set a timer and remove the other job
+	// 750ms later. Correct behavior would be to still run the job again in
+	// 250ms, but the bug would cause it to run instead 1s later.
+
+	var calls int
+	var mu sync.Mutex
+
+	cron := newWithSeconds()
+	hourJob := cron.Schedule(Every(time.Hour), FuncJob(func() {}))
+	cron.Schedule(Every(time.Second), FuncJob(func() {
+		mu.Lock()
+		defer mu.Unlock()
+		switch calls {
+		case 0:
+			wg1.Done()
+			calls++
+		case 1:
+			time.Sleep(750 * time.Millisecond)
+			cron.Remove(hourJob)
+			calls++
+		case 2:
+			calls++
+			wg2.Done()
+		case 3:
+			panic("unexpected 3rd call")
+		}
+	}))
+
+	cron.Start()
+	defer cron.Stop()
+
+	// the first run might be any length of time 0 - 1s, since the schedule
+	// rounds to the second. wait for the first run to true up.
+	wg1.Wait()
+
+	select {
+	case <-time.After(2 * OneSecond):
+		t.Error("expected job fires 2 times")
+	case <-wait(&wg2):
+	}
+}
+
+type ZeroSchedule struct{}
+
+func (*ZeroSchedule) Next(time.Time) time.Time {
+	return time.Time{}
+}
+
+// Tests that job without time does not run
+func TestJobWithZeroTimeDoesNotRun(t *testing.T) {
+	cron := newWithSeconds()
+	var calls int64
+	cron.AddFunc("* * * * * *", func() { atomic.AddInt64(&calls, 1) })
+	cron.Schedule(new(ZeroSchedule), FuncJob(func() { t.Error("expected zero task will not run") }))
+	cron.Start()
+	defer cron.Stop()
+	<-time.After(OneSecond)
+	if atomic.LoadInt64(&calls) != 1 {
+		t.Errorf("called %d times, expected 1\n", calls)
+	}
+}
+
+func TestStopAndWait(t *testing.T) {
+	t.Run("nothing running, returns immediately", func(*testing.T) {
+		cron := newWithSeconds()
+		cron.Start()
+		ctx := cron.Stop()
+		select {
+		case <-ctx.Done():
+		case <-time.After(time.Millisecond):
+			t.Error("context was not done immediately")
+		}
+	})
+
+	t.Run("repeated calls to Stop", func(*testing.T) {
+		cron := newWithSeconds()
+		cron.Start()
+		_ = cron.Stop()
+		time.Sleep(time.Millisecond)
+		ctx := cron.Stop()
+		select {
+		case <-ctx.Done():
+		case <-time.After(time.Millisecond):
+			t.Error("context was not done immediately")
+		}
+	})
+
+	t.Run("a couple fast jobs added, still returns immediately", func(*testing.T) {
+		cron := newWithSeconds()
+		cron.AddFunc("* * * * * *", func() {})
+		cron.Start()
+		cron.AddFunc("* * * * * *", func() {})
+		cron.AddFunc("* * * * * *", func() {})
+		cron.AddFunc("* * * * * *", func() {})
+		time.Sleep(time.Second)
+		ctx := cron.Stop()
+		select {
+		case <-ctx.Done():
+		case <-time.After(time.Millisecond):
+			t.Error("context was not done immediately")
+		}
+	})
+
+	t.Run("a couple fast jobs and a slow job added, waits for slow job", func(*testing.T) {
+		cron := newWithSeconds()
+		cron.AddFunc("* * * * * *", func() {})
+		cron.Start()
+		cron.AddFunc("* * * * * *", func() { time.Sleep(2 * time.Second) })
+		cron.AddFunc("* * * * * *", func() {})
+		time.Sleep(time.Second)
+
+		ctx := cron.Stop()
+
+		// Verify that it is not done for at least 750ms
+		select {
+		case <-ctx.Done():
+			t.Error("context was done too quickly immediately")
+		case <-time.After(750 * time.Millisecond):
+			// expected, because the job sleeping for 1 second is still running
+		}
+
+		// Verify that it IS done in the next 500ms (giving 250ms buffer)
+		select {
+		case <-ctx.Done():
+			// expected
+		case <-time.After(1500 * time.Millisecond):
+			t.Error("context not done after job should have completed")
+		}
+	})
+
+	t.Run("repeated calls to stop, waiting for completion and after", func(*testing.T) {
+		cron := newWithSeconds()
+		cron.AddFunc("* * * * * *", func() {})
+		cron.AddFunc("* * * * * *", func() { time.Sleep(2 * time.Second) })
+		cron.Start()
+		cron.AddFunc("* * * * * *", func() {})
+		time.Sleep(time.Second)
+		ctx := cron.Stop()
+		ctx2 := cron.Stop()
+
+		// Verify that it is not done for at least 1500ms
+		select {
+		case <-ctx.Done():
+			t.Error("context was done too quickly immediately")
+		case <-ctx2.Done():
+			t.Error("context2 was done too quickly immediately")
+		case <-time.After(1500 * time.Millisecond):
+			// expected, because the job sleeping for 2 seconds is still running
+		}
+
+		// Verify that it IS done in the next 1s (giving 500ms buffer)
+		select {
+		case <-ctx.Done():
+			// expected
+		case <-time.After(time.Second):
+			t.Error("context not done after job should have completed")
+		}
+
+		// Verify that ctx2 is also done.
+		select {
+		case <-ctx2.Done():
+			// expected
+		case <-time.After(time.Millisecond):
+			t.Error("context2 not done even though context1 is")
+		}
+
+		// Verify that a new context retrieved from stop is immediately done.
+		ctx3 := cron.Stop()
+		select {
+		case <-ctx3.Done():
+			// expected
+		case <-time.After(time.Millisecond):
+			t.Error("context not done even when cron Stop is completed")
+		}
+	})
+}
+
+func TestMultiThreadedStartAndStop(t *testing.T) {
+	cron := New()
+	go cron.Run()
+	time.Sleep(2 * time.Millisecond)
+	cron.Stop()
+}
+
+func wait(wg *sync.WaitGroup) chan bool {
+	ch := make(chan bool)
+	go func() {
+		wg.Wait()
+		ch <- true
+	}()
+	return ch
+}
+
+func stop(cron *Cron) chan bool {
+	ch := make(chan bool)
+	go func() {
+		cron.Stop()
+		ch <- true
+	}()
+	return ch
+}
+
+// newWithSeconds returns a Cron with the seconds field enabled.
+func newWithSeconds() *Cron {
+	return New(WithParser(secondParser), WithChain())
+}

plugin/cron/logger.go

@@ -0,0 +1,86 @@
+package cron
+
+import (
+	"io"
+	"log"
+	"os"
+	"strings"
+	"time"
+)
+
+// DefaultLogger is used by Cron if none is specified.
+var DefaultLogger = PrintfLogger(log.New(os.Stdout, "cron: ", log.LstdFlags))
+
+// DiscardLogger can be used by callers to discard all log messages.
+var DiscardLogger = PrintfLogger(log.New(io.Discard, "", 0))
+
+// Logger is the interface used in this package for logging, so that any backend
+// can be plugged in. It is a subset of the github.com/go-logr/logr interface.
+type Logger interface {
+	// Info logs routine messages about cron's operation.
+	Info(msg string, keysAndValues ...interface{})
+	// Error logs an error condition.
+	Error(err error, msg string, keysAndValues ...interface{})
+}
+
+// PrintfLogger wraps a Printf-based logger (such as the standard library "log")
+// into an implementation of the Logger interface which logs errors only.
+func PrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
+	return printfLogger{l, false}
+}
+
+// VerbosePrintfLogger wraps a Printf-based logger (such as the standard library
+// "log") into an implementation of the Logger interface which logs everything.
+func VerbosePrintfLogger(l interface{ Printf(string, ...interface{}) }) Logger {
+	return printfLogger{l, true}
+}
+
+type printfLogger struct {
+	logger  interface{ Printf(string, ...interface{}) }
+	logInfo bool
+}
+
+func (pl printfLogger) Info(msg string, keysAndValues ...interface{}) {
+	if pl.logInfo {
+		keysAndValues = formatTimes(keysAndValues)
+		pl.logger.Printf(
+			formatString(len(keysAndValues)),
+			append([]interface{}{msg}, keysAndValues...)...)
+	}
+}
+
+func (pl printfLogger) Error(err error, msg string, keysAndValues ...interface{}) {
+	keysAndValues = formatTimes(keysAndValues)
+	pl.logger.Printf(
+		formatString(len(keysAndValues)+2),
+		append([]interface{}{msg, "error", err}, keysAndValues...)...)
+}
+
+// formatString returns a logfmt-like format string for the number of
+// key/values.
+func formatString(numKeysAndValues int) string {
+	var sb strings.Builder
+	sb.WriteString("%s")
+	if numKeysAndValues > 0 {
+		sb.WriteString(", ")
+	}
+	for i := 0; i < numKeysAndValues/2; i++ {
+		if i > 0 {
+			sb.WriteString(", ")
+		}
+		sb.WriteString("%v=%v")
+	}
+	return sb.String()
+}
+
+// formatTimes formats any time.Time values as RFC3339.
+func formatTimes(keysAndValues []interface{}) []interface{} {
+	var formattedArgs []interface{}
+	for _, arg := range keysAndValues {
+		if t, ok := arg.(time.Time); ok {
+			arg = t.Format(time.RFC3339)
+		}
+		formattedArgs = append(formattedArgs, arg)
+	}
+	return formattedArgs
+}

plugin/cron/option.go

@@ -0,0 +1,45 @@
+package cron
+
+import (
+	"time"
+)
+
+// Option represents a modification to the default behavior of a Cron.
+type Option func(*Cron)
+
+// WithLocation overrides the timezone of the cron instance.
+func WithLocation(loc *time.Location) Option {
+	return func(c *Cron) {
+		c.location = loc
+	}
+}
+
+// WithSeconds overrides the parser used for interpreting job schedules to
+// include a seconds field as the first one.
+func WithSeconds() Option {
+	return WithParser(NewParser(
+		Second | Minute | Hour | Dom | Month | Dow | Descriptor,
+	))
+}
+
+// WithParser overrides the parser used for interpreting job schedules.
+func WithParser(p ScheduleParser) Option {
+	return func(c *Cron) {
+		c.parser = p
+	}
+}
+
+// WithChain specifies Job wrappers to apply to all jobs added to this cron.
+// Refer to the Chain* functions in this package for provided wrappers.
+func WithChain(wrappers ...JobWrapper) Option {
+	return func(c *Cron) {
+		c.chain = NewChain(wrappers...)
+	}
+}
+
+// WithLogger uses the provided logger.
+func WithLogger(logger Logger) Option {
+	return func(c *Cron) {
+		c.logger = logger
+	}
+}

plugin/cron/option_test.go

@@ -0,0 +1,43 @@
+//nolint:all
+package cron
+
+import (
+	"log"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestWithLocation(t *testing.T) {
+	c := New(WithLocation(time.UTC))
+	if c.location != time.UTC {
+		t.Errorf("expected UTC, got %v", c.location)
+	}
+}
+
+func TestWithParser(t *testing.T) {
+	var parser = NewParser(Dow)
+	c := New(WithParser(parser))
+	if c.parser != parser {
+		t.Error("expected provided parser")
+	}
+}
+
+func TestWithVerboseLogger(t *testing.T) {
+	var buf syncWriter
+	var logger = log.New(&buf, "", log.LstdFlags)
+	c := New(WithLogger(VerbosePrintfLogger(logger)))
+	if c.logger.(printfLogger).logger != logger {
+		t.Error("expected provided logger")
+	}
+
+	c.AddFunc("@every 1s", func() {})
+	c.Start()
+	time.Sleep(OneSecond)
+	c.Stop()
+	out := buf.String()
+	if !strings.Contains(out, "schedule,") ||
+		!strings.Contains(out, "run,") {
+		t.Error("expected to see some actions, got:", out)
+	}
+}

plugin/cron/parser.go

@@ -0,0 +1,437 @@
+package cron
+
+import (
+	"math"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// Configuration options for creating a parser. Most options specify which
+// fields should be included, while others enable features. If a field is not
+// included the parser will assume a default value. These options do not change
+// the order fields are parse in.
+type ParseOption int
+
+const (
+	Second         ParseOption = 1 << iota // Seconds field, default 0
+	SecondOptional                         // Optional seconds field, default 0
+	Minute                                 // Minutes field, default 0
+	Hour                                   // Hours field, default 0
+	Dom                                    // Day of month field, default *
+	Month                                  // Month field, default *
+	Dow                                    // Day of week field, default *
+	DowOptional                            // Optional day of week field, default *
+	Descriptor                             // Allow descriptors such as @monthly, @weekly, etc.
+)
+
+var places = []ParseOption{
+	Second,
+	Minute,
+	Hour,
+	Dom,
+	Month,
+	Dow,
+}
+
+var defaults = []string{
+	"0",
+	"0",
+	"0",
+	"*",
+	"*",
+	"*",
+}
+
+// A custom Parser that can be configured.
+type Parser struct {
+	options ParseOption
+}
+
+// NewParser creates a Parser with custom options.
+//
+// It panics if more than one Optional is given, since it would be impossible to
+// correctly infer which optional is provided or missing in general.
+//
+// Examples
+//
+//	// Standard parser without descriptors
+//	specParser := NewParser(Minute | Hour | Dom | Month | Dow)
+//	sched, err := specParser.Parse("0 0 15 */3 *")
+//
+//	// Same as above, just excludes time fields
+//	specParser := NewParser(Dom | Month | Dow)
+//	sched, err := specParser.Parse("15 */3 *")
+//
+//	// Same as above, just makes Dow optional
+//	specParser := NewParser(Dom | Month | DowOptional)
+//	sched, err := specParser.Parse("15 */3")
+func NewParser(options ParseOption) Parser {
+	optionals := 0
+	if options&DowOptional > 0 {
+		optionals++
+	}
+	if options&SecondOptional > 0 {
+		optionals++
+	}
+	if optionals > 1 {
+		panic("multiple optionals may not be configured")
+	}
+	return Parser{options}
+}
+
+// Parse returns a new crontab schedule representing the given spec.
+// It returns a descriptive error if the spec is not valid.
+// It accepts crontab specs and features configured by NewParser.
+func (p Parser) Parse(spec string) (Schedule, error) {
+	if len(spec) == 0 {
+		return nil, errors.New("empty spec string")
+	}
+
+	// Extract timezone if present
+	var loc = time.Local
+	if strings.HasPrefix(spec, "TZ=") || strings.HasPrefix(spec, "CRON_TZ=") {
+		var err error
+		i := strings.Index(spec, " ")
+		eq := strings.Index(spec, "=")
+		if loc, err = time.LoadLocation(spec[eq+1 : i]); err != nil {
+			return nil, errors.Wrap(err, "provided bad location")
+		}
+		spec = strings.TrimSpace(spec[i:])
+	}
+
+	// Handle named schedules (descriptors), if configured
+	if strings.HasPrefix(spec, "@") {
+		if p.options&Descriptor == 0 {
+			return nil, errors.New("descriptors not enabled")
+		}
+		return parseDescriptor(spec, loc)
+	}
+
+	// Split on whitespace.
+	fields := strings.Fields(spec)
+
+	// Validate & fill in any omitted or optional fields
+	var err error
+	fields, err = normalizeFields(fields, p.options)
+	if err != nil {
+		return nil, err
+	}
+
+	field := func(field string, r bounds) uint64 {
+		if err != nil {
+			return 0
+		}
+		var bits uint64
+		bits, err = getField(field, r)
+		return bits
+	}
+
+	var (
+		second     = field(fields[0], seconds)
+		minute     = field(fields[1], minutes)
+		hour       = field(fields[2], hours)
+		dayofmonth = field(fields[3], dom)
+		month      = field(fields[4], months)
+		dayofweek  = field(fields[5], dow)
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &SpecSchedule{
+		Second:   second,
+		Minute:   minute,
+		Hour:     hour,
+		Dom:      dayofmonth,
+		Month:    month,
+		Dow:      dayofweek,
+		Location: loc,
+	}, nil
+}
+
+// normalizeFields takes a subset set of the time fields and returns the full set
+// with defaults (zeroes) populated for unset fields.
+//
+// As part of performing this function, it also validates that the provided
+// fields are compatible with the configured options.
+func normalizeFields(fields []string, options ParseOption) ([]string, error) {
+	// Validate optionals & add their field to options
+	optionals := 0
+	if options&SecondOptional > 0 {
+		options |= Second
+		optionals++
+	}
+	if options&DowOptional > 0 {
+		options |= Dow
+		optionals++
+	}
+	if optionals > 1 {
+		return nil, errors.New("multiple optionals may not be configured")
+	}
+
+	// Figure out how many fields we need
+	max := 0
+	for _, place := range places {
+		if options&place > 0 {
+			max++
+		}
+	}
+	min := max - optionals
+
+	// Validate number of fields
+	if count := len(fields); count < min || count > max {
+		if min == max {
+			return nil, errors.New("incorrect number of fields")
+		}
+		return nil, errors.New("incorrect number of fields, expected " + strconv.Itoa(min) + "-" + strconv.Itoa(max))
+	}
+
+	// Populate the optional field if not provided
+	if min < max && len(fields) == min {
+		switch {
+		case options&DowOptional > 0:
+			fields = append(fields, defaults[5]) // TODO: improve access to default
+		case options&SecondOptional > 0:
+			fields = append([]string{defaults[0]}, fields...)
+		default:
+			return nil, errors.New("unexpected optional field")
+		}
+	}
+
+	// Populate all fields not part of options with their defaults
+	n := 0
+	expandedFields := make([]string, len(places))
+	copy(expandedFields, defaults)
+	for i, place := range places {
+		if options&place > 0 {
+			expandedFields[i] = fields[n]
+			n++
+		}
+	}
+	return expandedFields, nil
+}
+
+var standardParser = NewParser(
+	Minute | Hour | Dom | Month | Dow | Descriptor,
+)
+
+// ParseStandard returns a new crontab schedule representing the given
+// standardSpec (https://en.wikipedia.org/wiki/Cron). It requires 5 entries
+// representing: minute, hour, day of month, month and day of week, in that
+// order. It returns a descriptive error if the spec is not valid.
+//
+// It accepts
+//   - Standard crontab specs, e.g. "* * * * ?"
+//   - Descriptors, e.g. "@midnight", "@every 1h30m"
+func ParseStandard(standardSpec string) (Schedule, error) {
+	return standardParser.Parse(standardSpec)
+}
+
+// getField returns an Int with the bits set representing all of the times that
+// the field represents or error parsing field value.  A "field" is a comma-separated
+// list of "ranges".
+func getField(field string, r bounds) (uint64, error) {
+	var bits uint64
+	ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' })
+	for _, expr := range ranges {
+		bit, err := getRange(expr, r)
+		if err != nil {
+			return bits, err
+		}
+		bits |= bit
+	}
+	return bits, nil
+}
+
+// getRange returns the bits indicated by the given expression:
+//
+//	number | number "-" number [ "/" number ]
+//
+// or error parsing range.
+func getRange(expr string, r bounds) (uint64, error) {
+	var (
+		start, end, step uint
+		rangeAndStep     = strings.Split(expr, "/")
+		lowAndHigh       = strings.Split(rangeAndStep[0], "-")
+		singleDigit      = len(lowAndHigh) == 1
+		err              error
+	)
+
+	var extra uint64
+	if lowAndHigh[0] == "*" || lowAndHigh[0] == "?" {
+		start = r.min
+		end = r.max
+		extra = starBit
+	} else {
+		start, err = parseIntOrName(lowAndHigh[0], r.names)
+		if err != nil {
+			return 0, err
+		}
+		switch len(lowAndHigh) {
+		case 1:
+			end = start
+		case 2:
+			end, err = parseIntOrName(lowAndHigh[1], r.names)
+			if err != nil {
+				return 0, err
+			}
+		default:
+			return 0, errors.New("too many hyphens: " + expr)
+		}
+	}
+
+	switch len(rangeAndStep) {
+	case 1:
+		step = 1
+	case 2:
+		step, err = mustParseInt(rangeAndStep[1])
+		if err != nil {
+			return 0, err
+		}
+
+		// Special handling: "N/step" means "N-max/step".
+		if singleDigit {
+			end = r.max
+		}
+		if step > 1 {
+			extra = 0
+		}
+	default:
+		return 0, errors.New("too many slashes: " + expr)
+	}
+
+	if start < r.min {
+		return 0, errors.New("beginning of range below minimum: " + expr)
+	}
+	if end > r.max {
+		return 0, errors.New("end of range above maximum: " + expr)
+	}
+	if start > end {
+		return 0, errors.New("beginning of range after end: " + expr)
+	}
+	if step == 0 {
+		return 0, errors.New("step cannot be zero: " + expr)
+	}
+
+	return getBits(start, end, step) | extra, nil
+}
+
+// parseIntOrName returns the (possibly-named) integer contained in expr.
+func parseIntOrName(expr string, names map[string]uint) (uint, error) {
+	if names != nil {
+		if namedInt, ok := names[strings.ToLower(expr)]; ok {
+			return namedInt, nil
+		}
+	}
+	return mustParseInt(expr)
+}
+
+// mustParseInt parses the given expression as an int or returns an error.
+func mustParseInt(expr string) (uint, error) {
+	num, err := strconv.Atoi(expr)
+	if err != nil {
+		return 0, errors.Wrap(err, "failed to parse number")
+	}
+	if num < 0 {
+		return 0, errors.New("number must be positive")
+	}
+
+	return uint(num), nil
+}
+
+// getBits sets all bits in the range [min, max], modulo the given step size.
+func getBits(min, max, step uint) uint64 {
+	var bits uint64
+
+	// If step is 1, use shifts.
+	if step == 1 {
+		return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min)
+	}
+
+	// Else, use a simple loop.
+	for i := min; i <= max; i += step {
+		bits |= 1 << i
+	}
+	return bits
+}
+
+// all returns all bits within the given bounds.
+func all(r bounds) uint64 {
+	return getBits(r.min, r.max, 1) | starBit
+}
+
+// parseDescriptor returns a predefined schedule for the expression, or error if none matches.
+func parseDescriptor(descriptor string, loc *time.Location) (Schedule, error) {
+	switch descriptor {
+	case "@yearly", "@annually":
+		return &SpecSchedule{
+			Second:   1 << seconds.min,
+			Minute:   1 << minutes.min,
+			Hour:     1 << hours.min,
+			Dom:      1 << dom.min,
+			Month:    1 << months.min,
+			Dow:      all(dow),
+			Location: loc,
+		}, nil
+
+	case "@monthly":
+		return &SpecSchedule{
+			Second:   1 << seconds.min,
+			Minute:   1 << minutes.min,
+			Hour:     1 << hours.min,
+			Dom:      1 << dom.min,
+			Month:    all(months),
+			Dow:      all(dow),
+			Location: loc,
+		}, nil
+
+	case "@weekly":
+		return &SpecSchedule{
+			Second:   1 << seconds.min,
+			Minute:   1 << minutes.min,
+			Hour:     1 << hours.min,
+			Dom:      all(dom),
+			Month:    all(months),
+			Dow:      1 << dow.min,
+			Location: loc,
+		}, nil
+
+	case "@daily", "@midnight":
+		return &SpecSchedule{
+			Second:   1 << seconds.min,
+			Minute:   1 << minutes.min,
+			Hour:     1 << hours.min,
+			Dom:      all(dom),
+			Month:    all(months),
+			Dow:      all(dow),
+			Location: loc,
+		}, nil
+
+	case "@hourly":
+		return &SpecSchedule{
+			Second:   1 << seconds.min,
+			Minute:   1 << minutes.min,
+			Hour:     all(hours),
+			Dom:      all(dom),
+			Month:    all(months),
+			Dow:      all(dow),
+			Location: loc,
+		}, nil
+	default:
+		// Continue to check @every prefix below
+	}
+
+	const every = "@every "
+	if strings.HasPrefix(descriptor, every) {
+		duration, err := time.ParseDuration(descriptor[len(every):])
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to parse duration")
+		}
+		return Every(duration), nil
+	}
+
+	return nil, errors.New("unrecognized descriptor: " + descriptor)
+}

plugin/cron/parser_test.go

@@ -0,0 +1,384 @@
+//nolint:all
+package cron
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+var secondParser = NewParser(Second | Minute | Hour | Dom | Month | DowOptional | Descriptor)
+
+func TestRange(t *testing.T) {
+	zero := uint64(0)
+	ranges := []struct {
+		expr     string
+		min, max uint
+		expected uint64
+		err      string
+	}{
+		{"5", 0, 7, 1 << 5, ""},
+		{"0", 0, 7, 1 << 0, ""},
+		{"7", 0, 7, 1 << 7, ""},
+
+		{"5-5", 0, 7, 1 << 5, ""},
+		{"5-6", 0, 7, 1<<5 | 1<<6, ""},
+		{"5-7", 0, 7, 1<<5 | 1<<6 | 1<<7, ""},
+
+		{"5-6/2", 0, 7, 1 << 5, ""},
+		{"5-7/2", 0, 7, 1<<5 | 1<<7, ""},
+		{"5-7/1", 0, 7, 1<<5 | 1<<6 | 1<<7, ""},
+
+		{"*", 1, 3, 1<<1 | 1<<2 | 1<<3 | starBit, ""},
+		{"*/2", 1, 3, 1<<1 | 1<<3, ""},
+
+		{"5--5", 0, 0, zero, "too many hyphens"},
+		{"jan-x", 0, 0, zero, `failed to parse number: strconv.Atoi: parsing "jan": invalid syntax`},
+		{"2-x", 1, 5, zero, `failed to parse number: strconv.Atoi: parsing "x": invalid syntax`},
+		{"*/-12", 0, 0, zero, "number must be positive"},
+		{"*//2", 0, 0, zero, "too many slashes"},
+		{"1", 3, 5, zero, "below minimum"},
+		{"6", 3, 5, zero, "above maximum"},
+		{"5-3", 3, 5, zero, "beginning of range after end: 5-3"},
+		{"*/0", 0, 0, zero, "step cannot be zero: */0"},
+	}
+
+	for _, c := range ranges {
+		actual, err := getRange(c.expr, bounds{c.min, c.max, nil})
+		if len(c.err) != 0 && (err == nil || !strings.Contains(err.Error(), c.err)) {
+			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
+		}
+		if len(c.err) == 0 && err != nil {
+			t.Errorf("%s => unexpected error %v", c.expr, err)
+		}
+		if actual != c.expected {
+			t.Errorf("%s => expected %d, got %d", c.expr, c.expected, actual)
+		}
+	}
+}
+
+func TestField(t *testing.T) {
+	fields := []struct {
+		expr     string
+		min, max uint
+		expected uint64
+	}{
+		{"5", 1, 7, 1 << 5},
+		{"5,6", 1, 7, 1<<5 | 1<<6},
+		{"5,6,7", 1, 7, 1<<5 | 1<<6 | 1<<7},
+		{"1,5-7/2,3", 1, 7, 1<<1 | 1<<5 | 1<<7 | 1<<3},
+	}
+
+	for _, c := range fields {
+		actual, _ := getField(c.expr, bounds{c.min, c.max, nil})
+		if actual != c.expected {
+			t.Errorf("%s => expected %d, got %d", c.expr, c.expected, actual)
+		}
+	}
+}
+
+func TestAll(t *testing.T) {
+	allBits := []struct {
+		r        bounds
+		expected uint64
+	}{
+		{minutes, 0xfffffffffffffff}, // 0-59: 60 ones
+		{hours, 0xffffff},            // 0-23: 24 ones
+		{dom, 0xfffffffe},            // 1-31: 31 ones, 1 zero
+		{months, 0x1ffe},             // 1-12: 12 ones, 1 zero
+		{dow, 0x7f},                  // 0-6: 7 ones
+	}
+
+	for _, c := range allBits {
+		actual := all(c.r) // all() adds the starBit, so compensate for that..
+		if c.expected|starBit != actual {
+			t.Errorf("%d-%d/%d => expected %b, got %b",
+				c.r.min, c.r.max, 1, c.expected|starBit, actual)
+		}
+	}
+}
+
+func TestBits(t *testing.T) {
+	bits := []struct {
+		min, max, step uint
+		expected       uint64
+	}{
+		{0, 0, 1, 0x1},
+		{1, 1, 1, 0x2},
+		{1, 5, 2, 0x2a}, // 101010
+		{1, 4, 2, 0xa},  // 1010
+	}
+
+	for _, c := range bits {
+		actual := getBits(c.min, c.max, c.step)
+		if c.expected != actual {
+			t.Errorf("%d-%d/%d => expected %b, got %b",
+				c.min, c.max, c.step, c.expected, actual)
+		}
+	}
+}
+
+func TestParseScheduleErrors(t *testing.T) {
+	var tests = []struct{ expr, err string }{
+		{"* 5 j * * *", `failed to parse number: strconv.Atoi: parsing "j": invalid syntax`},
+		{"@every Xm", "failed to parse duration"},
+		{"@unrecognized", "unrecognized descriptor"},
+		{"* * * *", "incorrect number of fields, expected 5-6"},
+		{"", "empty spec string"},
+	}
+	for _, c := range tests {
+		actual, err := secondParser.Parse(c.expr)
+		if err == nil || !strings.Contains(err.Error(), c.err) {
+			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
+		}
+		if actual != nil {
+			t.Errorf("expected nil schedule on error, got %v", actual)
+		}
+	}
+}
+
+func TestParseSchedule(t *testing.T) {
+	tokyo, _ := time.LoadLocation("Asia/Tokyo")
+	entries := []struct {
+		parser   Parser
+		expr     string
+		expected Schedule
+	}{
+		{secondParser, "0 5 * * * *", every5min(time.Local)},
+		{standardParser, "5 * * * *", every5min(time.Local)},
+		{secondParser, "CRON_TZ=UTC  0 5 * * * *", every5min(time.UTC)},
+		{standardParser, "CRON_TZ=UTC  5 * * * *", every5min(time.UTC)},
+		{secondParser, "CRON_TZ=Asia/Tokyo 0 5 * * * *", every5min(tokyo)},
+		{secondParser, "@every 5m", ConstantDelaySchedule{5 * time.Minute}},
+		{secondParser, "@midnight", midnight(time.Local)},
+		{secondParser, "TZ=UTC  @midnight", midnight(time.UTC)},
+		{secondParser, "TZ=Asia/Tokyo @midnight", midnight(tokyo)},
+		{secondParser, "@yearly", annual(time.Local)},
+		{secondParser, "@annually", annual(time.Local)},
+		{
+			parser: secondParser,
+			expr:   "* 5 * * * *",
+			expected: &SpecSchedule{
+				Second:   all(seconds),
+				Minute:   1 << 5,
+				Hour:     all(hours),
+				Dom:      all(dom),
+				Month:    all(months),
+				Dow:      all(dow),
+				Location: time.Local,
+			},
+		},
+	}
+
+	for _, c := range entries {
+		actual, err := c.parser.Parse(c.expr)
+		if err != nil {
+			t.Errorf("%s => unexpected error %v", c.expr, err)
+		}
+		if !reflect.DeepEqual(actual, c.expected) {
+			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
+		}
+	}
+}
+
+func TestOptionalSecondSchedule(t *testing.T) {
+	parser := NewParser(SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor)
+	entries := []struct {
+		expr     string
+		expected Schedule
+	}{
+		{"0 5 * * * *", every5min(time.Local)},
+		{"5 5 * * * *", every5min5s(time.Local)},
+		{"5 * * * *", every5min(time.Local)},
+	}
+
+	for _, c := range entries {
+		actual, err := parser.Parse(c.expr)
+		if err != nil {
+			t.Errorf("%s => unexpected error %v", c.expr, err)
+		}
+		if !reflect.DeepEqual(actual, c.expected) {
+			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
+		}
+	}
+}
+
+func TestNormalizeFields(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []string
+		options  ParseOption
+		expected []string
+	}{
+		{
+			"AllFields_NoOptional",
+			[]string{"0", "5", "*", "*", "*", "*"},
+			Second | Minute | Hour | Dom | Month | Dow | Descriptor,
+			[]string{"0", "5", "*", "*", "*", "*"},
+		},
+		{
+			"AllFields_SecondOptional_Provided",
+			[]string{"0", "5", "*", "*", "*", "*"},
+			SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor,
+			[]string{"0", "5", "*", "*", "*", "*"},
+		},
+		{
+			"AllFields_SecondOptional_NotProvided",
+			[]string{"5", "*", "*", "*", "*"},
+			SecondOptional | Minute | Hour | Dom | Month | Dow | Descriptor,
+			[]string{"0", "5", "*", "*", "*", "*"},
+		},
+		{
+			"SubsetFields_NoOptional",
+			[]string{"5", "15", "*"},
+			Hour | Dom | Month,
+			[]string{"0", "0", "5", "15", "*", "*"},
+		},
+		{
+			"SubsetFields_DowOptional_Provided",
+			[]string{"5", "15", "*", "4"},
+			Hour | Dom | Month | DowOptional,
+			[]string{"0", "0", "5", "15", "*", "4"},
+		},
+		{
+			"SubsetFields_DowOptional_NotProvided",
+			[]string{"5", "15", "*"},
+			Hour | Dom | Month | DowOptional,
+			[]string{"0", "0", "5", "15", "*", "*"},
+		},
+		{
+			"SubsetFields_SecondOptional_NotProvided",
+			[]string{"5", "15", "*"},
+			SecondOptional | Hour | Dom | Month,
+			[]string{"0", "0", "5", "15", "*", "*"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(*testing.T) {
+			actual, err := normalizeFields(test.input, test.options)
+			if err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+			if !reflect.DeepEqual(actual, test.expected) {
+				t.Errorf("expected %v, got %v", test.expected, actual)
+			}
+		})
+	}
+}
+
+func TestNormalizeFields_Errors(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   []string
+		options ParseOption
+		err     string
+	}{
+		{
+			"TwoOptionals",
+			[]string{"0", "5", "*", "*", "*", "*"},
+			SecondOptional | Minute | Hour | Dom | Month | DowOptional,
+			"",
+		},
+		{
+			"TooManyFields",
+			[]string{"0", "5", "*", "*"},
+			SecondOptional | Minute | Hour,
+			"",
+		},
+		{
+			"NoFields",
+			[]string{},
+			SecondOptional | Minute | Hour,
+			"",
+		},
+		{
+			"TooFewFields",
+			[]string{"*"},
+			SecondOptional | Minute | Hour,
+			"",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(*testing.T) {
+			actual, err := normalizeFields(test.input, test.options)
+			if err == nil {
+				t.Errorf("expected an error, got none. results: %v", actual)
+			}
+			if !strings.Contains(err.Error(), test.err) {
+				t.Errorf("expected error %q, got %q", test.err, err.Error())
+			}
+		})
+	}
+}
+
+func TestStandardSpecSchedule(t *testing.T) {
+	entries := []struct {
+		expr     string
+		expected Schedule
+		err      string
+	}{
+		{
+			expr:     "5 * * * *",
+			expected: &SpecSchedule{1 << seconds.min, 1 << 5, all(hours), all(dom), all(months), all(dow), time.Local},
+		},
+		{
+			expr:     "@every 5m",
+			expected: ConstantDelaySchedule{time.Duration(5) * time.Minute},
+		},
+		{
+			expr: "5 j * * *",
+			err:  `failed to parse number: strconv.Atoi: parsing "j": invalid syntax`,
+		},
+		{
+			expr: "* * * *",
+			err:  "incorrect number of fields",
+		},
+	}
+
+	for _, c := range entries {
+		actual, err := ParseStandard(c.expr)
+		if len(c.err) != 0 && (err == nil || !strings.Contains(err.Error(), c.err)) {
+			t.Errorf("%s => expected %v, got %v", c.expr, c.err, err)
+		}
+		if len(c.err) == 0 && err != nil {
+			t.Errorf("%s => unexpected error %v", c.expr, err)
+		}
+		if !reflect.DeepEqual(actual, c.expected) {
+			t.Errorf("%s => expected %b, got %b", c.expr, c.expected, actual)
+		}
+	}
+}
+
+func TestNoDescriptorParser(t *testing.T) {
+	parser := NewParser(Minute | Hour)
+	_, err := parser.Parse("@every 1m")
+	if err == nil {
+		t.Error("expected an error, got none")
+	}
+}
+
+func every5min(loc *time.Location) *SpecSchedule {
+	return &SpecSchedule{1 << 0, 1 << 5, all(hours), all(dom), all(months), all(dow), loc}
+}
+
+func every5min5s(loc *time.Location) *SpecSchedule {
+	return &SpecSchedule{1 << 5, 1 << 5, all(hours), all(dom), all(months), all(dow), loc}
+}
+
+func midnight(loc *time.Location) *SpecSchedule {
+	return &SpecSchedule{1, 1, 1, all(dom), all(months), all(dow), loc}
+}
+
+func annual(loc *time.Location) *SpecSchedule {
+	return &SpecSchedule{
+		Second:   1 << seconds.min,
+		Minute:   1 << minutes.min,
+		Hour:     1 << hours.min,
+		Dom:      1 << dom.min,
+		Month:    1 << months.min,
+		Dow:      all(dow),
+		Location: loc,
+	}
+}

plugin/cron/spec.go

@@ -0,0 +1,188 @@
+package cron
+
+import "time"
+
+// SpecSchedule specifies a duty cycle (to the second granularity), based on a
+// traditional crontab specification. It is computed initially and stored as bit sets.
+type SpecSchedule struct {
+	Second, Minute, Hour, Dom, Month, Dow uint64
+
+	// Override location for this schedule.
+	Location *time.Location
+}
+
+// bounds provides a range of acceptable values (plus a map of name to value).
+type bounds struct {
+	min, max uint
+	names    map[string]uint
+}
+
+// The bounds for each field.
+var (
+	seconds = bounds{0, 59, nil}
+	minutes = bounds{0, 59, nil}
+	hours   = bounds{0, 23, nil}
+	dom     = bounds{1, 31, nil}
+	months  = bounds{1, 12, map[string]uint{
+		"jan": 1,
+		"feb": 2,
+		"mar": 3,
+		"apr": 4,
+		"may": 5,
+		"jun": 6,
+		"jul": 7,
+		"aug": 8,
+		"sep": 9,
+		"oct": 10,
+		"nov": 11,
+		"dec": 12,
+	}}
+	dow = bounds{0, 6, map[string]uint{
+		"sun": 0,
+		"mon": 1,
+		"tue": 2,
+		"wed": 3,
+		"thu": 4,
+		"fri": 5,
+		"sat": 6,
+	}}
+)
+
+const (
+	// Set the top bit if a star was included in the expression.
+	starBit = 1 << 63
+)
+
+// Next returns the next time this schedule is activated, greater than the given
+// time.  If no time can be found to satisfy the schedule, return the zero time.
+func (s *SpecSchedule) Next(t time.Time) time.Time {
+	// General approach
+	//
+	// For Month, Day, Hour, Minute, Second:
+	// Check if the time value matches.  If yes, continue to the next field.
+	// If the field doesn't match the schedule, then increment the field until it matches.
+	// While incrementing the field, a wrap-around brings it back to the beginning
+	// of the field list (since it is necessary to re-verify previous field
+	// values)
+
+	// Convert the given time into the schedule's timezone, if one is specified.
+	// Save the original timezone so we can convert back after we find a time.
+	// Note that schedules without a time zone specified (time.Local) are treated
+	// as local to the time provided.
+	origLocation := t.Location()
+	loc := s.Location
+	if loc == time.Local {
+		loc = t.Location()
+	}
+	if s.Location != time.Local {
+		t = t.In(s.Location)
+	}
+
+	// Start at the earliest possible time (the upcoming second).
+	t = t.Add(1*time.Second - time.Duration(t.Nanosecond())*time.Nanosecond)
+
+	// This flag indicates whether a field has been incremented.
+	added := false
+
+	// If no time is found within five years, return zero.
+	yearLimit := t.Year() + 5
+
+WRAP:
+	if t.Year() > yearLimit {
+		return time.Time{}
+	}
+
+	// Find the first applicable month.
+	// If it's this month, then do nothing.
+	for 1<<uint(t.Month())&s.Month == 0 {
+		// If we have to add a month, reset the other parts to 0.
+		if !added {
+			added = true
+			// Otherwise, set the date at the beginning (since the current time is irrelevant).
+			t = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
+		}
+		t = t.AddDate(0, 1, 0)
+
+		// Wrapped around.
+		if t.Month() == time.January {
+			goto WRAP
+		}
+	}
+
+	// Now get a day in that month.
+	//
+	// NOTE: This causes issues for daylight savings regimes where midnight does
+	// not exist.  For example: Sao Paulo has DST that transforms midnight on
+	// 11/3 into 1am. Handle that by noticing when the Hour ends up != 0.
+	for !dayMatches(s, t) {
+		if !added {
+			added = true
+			t = time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
+		}
+		t = t.AddDate(0, 0, 1)
+		// Notice if the hour is no longer midnight due to DST.
+		// Add an hour if it's 23, subtract an hour if it's 1.
+		if t.Hour() != 0 {
+			if t.Hour() > 12 {
+				t = t.Add(time.Duration(24-t.Hour()) * time.Hour)
+			} else {
+				t = t.Add(time.Duration(-t.Hour()) * time.Hour)
+			}
+		}
+
+		if t.Day() == 1 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Hour())&s.Hour == 0 {
+		if !added {
+			added = true
+			t = time.Date(t.Year(), t.Month(), t.Day(), t.Hour(), 0, 0, 0, loc)
+		}
+		t = t.Add(1 * time.Hour)
+
+		if t.Hour() == 0 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Minute())&s.Minute == 0 {
+		if !added {
+			added = true
+			t = t.Truncate(time.Minute)
+		}
+		t = t.Add(1 * time.Minute)
+
+		if t.Minute() == 0 {
+			goto WRAP
+		}
+	}
+
+	for 1<<uint(t.Second())&s.Second == 0 {
+		if !added {
+			added = true
+			t = t.Truncate(time.Second)
+		}
+		t = t.Add(1 * time.Second)
+
+		if t.Second() == 0 {
+			goto WRAP
+		}
+	}
+
+	return t.In(origLocation)
+}
+
+// dayMatches returns true if the schedule's day-of-week and day-of-month
+// restrictions are satisfied by the given time.
+func dayMatches(s *SpecSchedule, t time.Time) bool {
+	var (
+		domMatch = 1<<uint(t.Day())&s.Dom > 0
+		dowMatch = 1<<uint(t.Weekday())&s.Dow > 0
+	)
+	if s.Dom&starBit > 0 || s.Dow&starBit > 0 {
+		return domMatch && dowMatch
+	}
+	return domMatch || dowMatch
+}

plugin/cron/spec_test.go

@@ -0,0 +1,301 @@
+//nolint:all
+package cron
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestActivation(t *testing.T) {
+	tests := []struct {
+		time, spec string
+		expected   bool
+	}{
+		// Every fifteen minutes.
+		{"Mon Jul 9 15:00 2012", "0/15 * * * *", true},
+		{"Mon Jul 9 15:45 2012", "0/15 * * * *", true},
+		{"Mon Jul 9 15:40 2012", "0/15 * * * *", false},
+
+		// Every fifteen minutes, starting at 5 minutes.
+		{"Mon Jul 9 15:05 2012", "5/15 * * * *", true},
+		{"Mon Jul 9 15:20 2012", "5/15 * * * *", true},
+		{"Mon Jul 9 15:50 2012", "5/15 * * * *", true},
+
+		// Named months
+		{"Sun Jul 15 15:00 2012", "0/15 * * Jul *", true},
+		{"Sun Jul 15 15:00 2012", "0/15 * * Jun *", false},
+
+		// Everything set.
+		{"Sun Jul 15 08:30 2012", "30 08 ? Jul Sun", true},
+		{"Sun Jul 15 08:30 2012", "30 08 15 Jul ?", true},
+		{"Mon Jul 16 08:30 2012", "30 08 ? Jul Sun", false},
+		{"Mon Jul 16 08:30 2012", "30 08 15 Jul ?", false},
+
+		// Predefined schedules
+		{"Mon Jul 9 15:00 2012", "@hourly", true},
+		{"Mon Jul 9 15:04 2012", "@hourly", false},
+		{"Mon Jul 9 15:00 2012", "@daily", false},
+		{"Mon Jul 9 00:00 2012", "@daily", true},
+		{"Mon Jul 9 00:00 2012", "@weekly", false},
+		{"Sun Jul 8 00:00 2012", "@weekly", true},
+		{"Sun Jul 8 01:00 2012", "@weekly", false},
+		{"Sun Jul 8 00:00 2012", "@monthly", false},
+		{"Sun Jul 1 00:00 2012", "@monthly", true},
+
+		// Test interaction of DOW and DOM.
+		// If both are restricted, then only one needs to match.
+		{"Sun Jul 15 00:00 2012", "* * 1,15 * Sun", true},
+		{"Fri Jun 15 00:00 2012", "* * 1,15 * Sun", true},
+		{"Wed Aug 1 00:00 2012", "* * 1,15 * Sun", true},
+		{"Sun Jul 15 00:00 2012", "* * */10 * Sun", true}, // verifies #70
+
+		// However, if one has a star, then both need to match.
+		{"Sun Jul 15 00:00 2012", "* * * * Mon", false},
+		{"Mon Jul 9 00:00 2012", "* * 1,15 * *", false},
+		{"Sun Jul 15 00:00 2012", "* * 1,15 * *", true},
+		{"Sun Jul 15 00:00 2012", "* * */2 * Sun", true},
+	}
+
+	for _, test := range tests {
+		sched, err := ParseStandard(test.spec)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		actual := sched.Next(getTime(test.time).Add(-1 * time.Second))
+		expected := getTime(test.time)
+		if test.expected && expected != actual || !test.expected && expected == actual {
+			t.Errorf("Fail evaluating %s on %s: (expected) %s != %s (actual)",
+				test.spec, test.time, expected, actual)
+		}
+	}
+}
+
+func TestNext(t *testing.T) {
+	runs := []struct {
+		time, spec string
+		expected   string
+	}{
+		// Simple cases
+		{"Mon Jul 9 14:45 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},
+		{"Mon Jul 9 14:59 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},
+		{"Mon Jul 9 14:59:59 2012", "0 0/15 * * * *", "Mon Jul 9 15:00 2012"},
+
+		// Wrap around hours
+		{"Mon Jul 9 15:45 2012", "0 20-35/15 * * * *", "Mon Jul 9 16:20 2012"},
+
+		// Wrap around days
+		{"Mon Jul 9 23:46 2012", "0 */15 * * * *", "Tue Jul 10 00:00 2012"},
+		{"Mon Jul 9 23:45 2012", "0 20-35/15 * * * *", "Tue Jul 10 00:20 2012"},
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * * * *", "Tue Jul 10 00:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 1/2 * * *", "Tue Jul 10 01:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 10-12 * * *", "Tue Jul 10 10:20:15 2012"},
+
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 1/2 */2 * *", "Thu Jul 11 01:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * 9-20 * *", "Wed Jul 10 00:20:15 2012"},
+		{"Mon Jul 9 23:35:51 2012", "15/35 20-35/15 * 9-20 Jul *", "Wed Jul 10 00:20:15 2012"},
+
+		// Wrap around months
+		{"Mon Jul 9 23:35 2012", "0 0 0 9 Apr-Oct ?", "Thu Aug 9 00:00 2012"},
+		{"Mon Jul 9 23:35 2012", "0 0 0 */5 Apr,Aug,Oct Mon", "Tue Aug 1 00:00 2012"},
+		{"Mon Jul 9 23:35 2012", "0 0 0 */5 Oct Mon", "Mon Oct 1 00:00 2012"},
+
+		// Wrap around years
+		{"Mon Jul 9 23:35 2012", "0 0 0 * Feb Mon", "Mon Feb 4 00:00 2013"},
+		{"Mon Jul 9 23:35 2012", "0 0 0 * Feb Mon/2", "Fri Feb 1 00:00 2013"},
+
+		// Wrap around minute, hour, day, month, and year
+		{"Mon Dec 31 23:59:45 2012", "0 * * * * *", "Tue Jan 1 00:00:00 2013"},
+
+		// Leap year
+		{"Mon Jul 9 23:35 2012", "0 0 0 29 Feb ?", "Mon Feb 29 00:00 2016"},
+
+		// Daylight savings time 2am EST (-5) -> 3am EDT (-4)
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 30 2 11 Mar ?", "2013-03-11T02:30:00-0400"},
+
+		// hourly job
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T01:00:00-0500"},
+		{"2012-03-11T01:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T03:00:00-0400"},
+		{"2012-03-11T03:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T04:00:00-0400"},
+		{"2012-03-11T04:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-03-11T05:00:00-0400"},
+
+		// hourly job using CRON_TZ
+		{"2012-03-11T00:00:00-0500", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T01:00:00-0500"},
+		{"2012-03-11T01:00:00-0500", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T03:00:00-0400"},
+		{"2012-03-11T03:00:00-0400", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T04:00:00-0400"},
+		{"2012-03-11T04:00:00-0400", "CRON_TZ=America/New_York 0 0 * * * ?", "2012-03-11T05:00:00-0400"},
+
+		// 1am nightly job
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-11T01:00:00-0500"},
+		{"2012-03-11T01:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-03-12T01:00:00-0400"},
+
+		// 2am nightly job (skipped)
+		{"2012-03-11T00:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-03-12T02:00:00-0400"},
+
+		// Daylight savings time 2am EDT (-4) => 1am EST (-5)
+		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 30 2 04 Nov ?", "2012-11-04T02:30:00-0500"},
+		{"2012-11-04T01:45:00-0400", "TZ=America/New_York 0 30 1 04 Nov ?", "2012-11-04T01:30:00-0500"},
+
+		// hourly job
+		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T01:00:00-0400"},
+		{"2012-11-04T01:00:00-0400", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T01:00:00-0500"},
+		{"2012-11-04T01:00:00-0500", "TZ=America/New_York 0 0 * * * ?", "2012-11-04T02:00:00-0500"},
+
+		// 1am nightly job (runs twice)
+		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
+		{"2012-11-04T01:00:00-0400", "TZ=America/New_York 0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
+		{"2012-11-04T01:00:00-0500", "TZ=America/New_York 0 0 1 * * ?", "2012-11-05T01:00:00-0500"},
+
+		// 2am nightly job
+		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
+		{"2012-11-04T02:00:00-0500", "TZ=America/New_York 0 0 2 * * ?", "2012-11-05T02:00:00-0500"},
+
+		// 3am nightly job
+		{"2012-11-04T00:00:00-0400", "TZ=America/New_York 0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
+		{"2012-11-04T03:00:00-0500", "TZ=America/New_York 0 0 3 * * ?", "2012-11-05T03:00:00-0500"},
+
+		// hourly job
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0400"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 * * * ?", "2012-11-04T01:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 * * * ?", "2012-11-04T02:00:00-0500"},
+
+		// 1am nightly job (runs twice)
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0400"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0400", "0 0 1 * * ?", "2012-11-04T01:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T01:00:00-0500", "0 0 1 * * ?", "2012-11-05T01:00:00-0500"},
+
+		// 2am nightly job
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 2 * * ?", "2012-11-04T02:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T02:00:00-0500", "0 0 2 * * ?", "2012-11-05T02:00:00-0500"},
+
+		// 3am nightly job
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 * * ?", "2012-11-04T03:00:00-0500"},
+		{"TZ=America/New_York 2012-11-04T03:00:00-0500", "0 0 3 * * ?", "2012-11-05T03:00:00-0500"},
+
+		// Unsatisfiable
+		{"Mon Jul 9 23:35 2012", "0 0 0 30 Feb ?", ""},
+		{"Mon Jul 9 23:35 2012", "0 0 0 31 Apr ?", ""},
+
+		// Monthly job
+		{"TZ=America/New_York 2012-11-04T00:00:00-0400", "0 0 3 3 * ?", "2012-12-03T03:00:00-0500"},
+
+		// Test the scenario of DST resulting in midnight not being a valid time.
+		// https://github.com/robfig/cron/issues/157
+		{"2018-10-17T05:00:00-0400", "TZ=America/Sao_Paulo 0 0 9 10 * ?", "2018-11-10T06:00:00-0500"},
+		{"2018-02-14T05:00:00-0500", "TZ=America/Sao_Paulo 0 0 9 22 * ?", "2018-02-22T07:00:00-0500"},
+	}
+
+	for _, c := range runs {
+		sched, err := secondParser.Parse(c.spec)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		actual := sched.Next(getTime(c.time))
+		expected := getTime(c.expected)
+		if !actual.Equal(expected) {
+			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.spec, expected, actual)
+		}
+	}
+}
+
+func TestErrors(t *testing.T) {
+	invalidSpecs := []string{
+		"xyz",
+		"60 0 * * *",
+		"0 60 * * *",
+		"0 0 * * XYZ",
+	}
+	for _, spec := range invalidSpecs {
+		_, err := ParseStandard(spec)
+		if err == nil {
+			t.Error("expected an error parsing: ", spec)
+		}
+	}
+}
+
+func getTime(value string) time.Time {
+	if value == "" {
+		return time.Time{}
+	}
+
+	var location = time.Local
+	if strings.HasPrefix(value, "TZ=") {
+		parts := strings.Fields(value)
+		loc, err := time.LoadLocation(parts[0][len("TZ="):])
+		if err != nil {
+			panic("could not parse location:" + err.Error())
+		}
+		location = loc
+		value = parts[1]
+	}
+
+	var layouts = []string{
+		"Mon Jan 2 15:04 2006",
+		"Mon Jan 2 15:04:05 2006",
+	}
+	for _, layout := range layouts {
+		if t, err := time.ParseInLocation(layout, value, location); err == nil {
+			return t
+		}
+	}
+	if t, err := time.ParseInLocation("2006-01-02T15:04:05-0700", value, location); err == nil {
+		return t
+	}
+	panic("could not parse time value " + value)
+}
+
+func TestNextWithTz(t *testing.T) {
+	runs := []struct {
+		time, spec string
+		expected   string
+	}{
+		// Failing tests
+		{"2016-01-03T13:09:03+0530", "14 14 * * *", "2016-01-03T14:14:00+0530"},
+		{"2016-01-03T04:09:03+0530", "14 14 * * ?", "2016-01-03T14:14:00+0530"},
+
+		// Passing tests
+		{"2016-01-03T14:09:03+0530", "14 14 * * *", "2016-01-03T14:14:00+0530"},
+		{"2016-01-03T14:00:00+0530", "14 14 * * ?", "2016-01-03T14:14:00+0530"},
+	}
+	for _, c := range runs {
+		sched, err := ParseStandard(c.spec)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		actual := sched.Next(getTimeTZ(c.time))
+		expected := getTimeTZ(c.expected)
+		if !actual.Equal(expected) {
+			t.Errorf("%s, \"%s\": (expected) %v != %v (actual)", c.time, c.spec, expected, actual)
+		}
+	}
+}
+
+func getTimeTZ(value string) time.Time {
+	if value == "" {
+		return time.Time{}
+	}
+	t, err := time.Parse("Mon Jan 2 15:04 2006", value)
+	if err != nil {
+		t, err = time.Parse("Mon Jan 2 15:04:05 2006", value)
+		if err != nil {
+			t, err = time.Parse("2006-01-02T15:04:05-0700", value)
+			if err != nil {
+				panic(err)
+			}
+		}
+	}
+
+	return t
+}
+
+// https://github.com/robfig/cron/issues/144
+func TestSlash0NoHang(t *testing.T) {
+	schedule := "TZ=America/New_York 15/0 * * * *"
+	_, err := ParseStandard(schedule)
+	if err == nil {
+		t.Error("expected an error on 0 increment")
+	}
+}

plugin/email/README.md

@@ -0,0 +1,507 @@
+# Email Plugin
+
+SMTP email sending functionality for self-hosted Memos instances.
+
+## Overview
+
+This plugin provides a simple, reliable email sending interface following industry-standard SMTP protocols. It's designed for self-hosted environments where instance administrators configure their own email service, similar to platforms like GitHub, GitLab, and Discourse.
+
+## Features
+
+- Standard SMTP protocol support
+- TLS/STARTTLS and SSL/TLS encryption
+- HTML and plain text emails
+- Multiple recipients (To, Cc, Bcc)
+- Synchronous and asynchronous sending
+- Detailed error reporting with context
+- Works with all major email providers
+- Reply-To header support
+- RFC 5322 compliant message formatting
+
+## Quick Start
+
+### 1. Configure SMTP Settings
+
+```go
+import "github.com/usememos/memos/plugin/email"
+
+config := &email.Config{
+    SMTPHost:     "smtp.gmail.com",
+    SMTPPort:     587,
+    SMTPUsername: "your-email@gmail.com",
+    SMTPPassword: "your-app-password",
+    FromEmail:    "noreply@yourdomain.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+### 2. Create and Send Email
+
+```go
+message := &email.Message{
+    To:      []string{"user@example.com"},
+    Subject: "Welcome to Memos!",
+    Body:    "Thanks for signing up.",
+    IsHTML:  false,
+}
+
+// Synchronous send (waits for result)
+err := email.Send(config, message)
+if err != nil {
+    log.Printf("Failed to send email: %v", err)
+}
+
+// Asynchronous send (returns immediately)
+email.SendAsync(config, message)
+```
+
+## Provider Configuration
+
+### Gmail
+
+Requires an [App Password](https://support.google.com/accounts/answer/185833) (2FA must be enabled):
+
+```go
+config := &email.Config{
+    SMTPHost:     "smtp.gmail.com",
+    SMTPPort:     587,
+    SMTPUsername: "your-email@gmail.com",
+    SMTPPassword: "your-16-char-app-password",
+    FromEmail:    "your-email@gmail.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+**Alternative (SSL):**
+```go
+config := &email.Config{
+    SMTPHost:     "smtp.gmail.com",
+    SMTPPort:     465,
+    SMTPUsername: "your-email@gmail.com",
+    SMTPPassword: "your-16-char-app-password",
+    FromEmail:    "your-email@gmail.com",
+    FromName:     "Memos",
+    UseSSL:       true,
+}
+```
+
+### SendGrid
+
+```go
+config := &email.Config{
+    SMTPHost:     "smtp.sendgrid.net",
+    SMTPPort:     587,
+    SMTPUsername: "apikey",
+    SMTPPassword: "your-sendgrid-api-key",
+    FromEmail:    "noreply@yourdomain.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+### AWS SES
+
+```go
+config := &email.Config{
+    SMTPHost:     "email-smtp.us-east-1.amazonaws.com",
+    SMTPPort:     587,
+    SMTPUsername: "your-smtp-username",
+    SMTPPassword: "your-smtp-password",
+    FromEmail:    "verified@yourdomain.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+**Note:** Replace `us-east-1` with your AWS region. Email must be verified in SES.
+
+### Mailgun
+
+```go
+config := &email.Config{
+    SMTPHost:     "smtp.mailgun.org",
+    SMTPPort:     587,
+    SMTPUsername: "postmaster@yourdomain.com",
+    SMTPPassword: "your-mailgun-smtp-password",
+    FromEmail:    "noreply@yourdomain.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+### Self-Hosted SMTP (Postfix, Exim, etc.)
+
+```go
+config := &email.Config{
+    SMTPHost:     "mail.yourdomain.com",
+    SMTPPort:     587,
+    SMTPUsername: "username",
+    SMTPPassword: "password",
+    FromEmail:    "noreply@yourdomain.com",
+    FromName:     "Memos",
+    UseTLS:       true,
+}
+```
+
+## HTML Emails
+
+```go
+message := &email.Message{
+    To:      []string{"user@example.com"},
+    Subject: "Welcome to Memos!",
+    Body: `
+<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="UTF-8">
+</head>
+<body style="font-family: Arial, sans-serif;">
+    <h1 style="color: #333;">Welcome to Memos!</h1>
+    <p>We're excited to have you on board.</p>
+    <a href="https://yourdomain.com" style="background-color: #4CAF50; color: white; padding: 10px 20px; text-decoration: none; border-radius: 5px;">Get Started</a>
+</body>
+</html>
+    `,
+    IsHTML: true,
+}
+
+email.Send(config, message)
+```
+
+## Multiple Recipients
+
+```go
+message := &email.Message{
+    To:      []string{"user1@example.com", "user2@example.com"},
+    Cc:      []string{"manager@example.com"},
+    Bcc:     []string{"admin@example.com"},
+    Subject: "Team Update",
+    Body:    "Important team announcement...",
+    ReplyTo: "support@yourdomain.com",
+}
+
+email.Send(config, message)
+```
+
+## Testing
+
+### Run Tests
+
+```bash
+# All tests
+go test ./plugin/email/... -v
+
+# With coverage
+go test ./plugin/email/... -v -cover
+
+# With race detector
+go test ./plugin/email/... -race
+```
+
+### Manual Testing
+
+Create a simple test program:
+
+```go
+package main
+
+import (
+    "log"
+    "github.com/usememos/memos/plugin/email"
+)
+
+func main() {
+    config := &email.Config{
+        SMTPHost:     "smtp.gmail.com",
+        SMTPPort:     587,
+        SMTPUsername: "your-email@gmail.com",
+        SMTPPassword: "your-app-password",
+        FromEmail:    "your-email@gmail.com",
+        FromName:     "Test",
+        UseTLS:       true,
+    }
+
+    message := &email.Message{
+        To:      []string{"recipient@example.com"},
+        Subject: "Test Email",
+        Body:    "This is a test email from Memos email plugin.",
+    }
+
+    if err := email.Send(config, message); err != nil {
+        log.Fatalf("Failed to send email: %v", err)
+    }
+
+    log.Println("Email sent successfully!")
+}
+```
+
+## Security Best Practices
+
+### 1. Use TLS/SSL Encryption
+
+Always enable encryption in production:
+
+```go
+// STARTTLS (port 587) - Recommended
+config.UseTLS = true
+
+// SSL/TLS (port 465)
+config.UseSSL = true
+```
+
+### 2. Secure Credential Storage
+
+Never hardcode credentials. Use environment variables:
+
+```go
+import "os"
+
+config := &email.Config{
+    SMTPHost:     os.Getenv("SMTP_HOST"),
+    SMTPPort:     587,
+    SMTPUsername: os.Getenv("SMTP_USERNAME"),
+    SMTPPassword: os.Getenv("SMTP_PASSWORD"),
+    FromEmail:    os.Getenv("SMTP_FROM_EMAIL"),
+    UseTLS:       true,
+}
+```
+
+### 3. Use App-Specific Passwords
+
+For Gmail and similar services, use app passwords instead of your main account password.
+
+### 4. Validate and Sanitize Input
+
+Always validate email addresses and sanitize content:
+
+```go
+// Validate before sending
+if err := message.Validate(); err != nil {
+    return err
+}
+```
+
+### 5. Implement Rate Limiting
+
+Prevent abuse by limiting email sending:
+
+```go
+// Example using golang.org/x/time/rate
+limiter := rate.NewLimiter(rate.Every(time.Second), 10) // 10 emails per second
+
+if !limiter.Allow() {
+    return errors.New("rate limit exceeded")
+}
+```
+
+### 6. Monitor and Log
+
+Log email sending activity for security monitoring:
+
+```go
+if err := email.Send(config, message); err != nil {
+    slog.Error("Email send failed",
+        slog.String("recipient", message.To[0]),
+        slog.Any("error", err))
+}
+```
+
+## Common Ports
+
+| Port | Protocol | Security | Use Case |
+|------|----------|----------|----------|
+| **587** | SMTP + STARTTLS | Encrypted | **Recommended** for most providers |
+| **465** | SMTP over SSL/TLS | Encrypted | Alternative secure option |
+| **25** | SMTP | Unencrypted | Legacy, often blocked by ISPs |
+| **2525** | SMTP + STARTTLS | Encrypted | Alternative when 587 is blocked |
+
+**Port 587 (STARTTLS)** is the recommended standard for modern SMTP:
+```go
+config := &email.Config{
+    SMTPPort: 587,
+    UseTLS:   true,
+}
+```
+
+**Port 465 (SSL/TLS)** is the alternative:
+```go
+config := &email.Config{
+    SMTPPort: 465,
+    UseSSL:   true,
+}
+```
+
+## Error Handling
+
+The package provides detailed, contextual errors:
+
+```go
+err := email.Send(config, message)
+if err != nil {
+    // Error messages include context:
+    switch {
+    case strings.Contains(err.Error(), "invalid email configuration"):
+        // Configuration error (missing host, invalid port, etc.)
+        log.Printf("Configuration error: %v", err)
+
+    case strings.Contains(err.Error(), "invalid email message"):
+        // Message validation error (missing recipients, subject, body)
+        log.Printf("Message error: %v", err)
+
+    case strings.Contains(err.Error(), "authentication failed"):
+        // SMTP authentication failed (wrong credentials)
+        log.Printf("Auth error: %v", err)
+
+    case strings.Contains(err.Error(), "failed to connect"):
+        // Network/connection error
+        log.Printf("Connection error: %v", err)
+
+    case strings.Contains(err.Error(), "recipient rejected"):
+        // SMTP server rejected recipient
+        log.Printf("Recipient error: %v", err)
+
+    default:
+        log.Printf("Unknown error: %v", err)
+    }
+}
+```
+
+### Common Error Messages
+
+```
+❌ "invalid email configuration: SMTP host is required"
+   → Fix: Set config.SMTPHost
+
+❌ "invalid email configuration: SMTP port must be between 1 and 65535"
+   → Fix: Set valid config.SMTPPort (usually 587 or 465)
+
+❌ "invalid email configuration: from email is required"
+   → Fix: Set config.FromEmail
+
+❌ "invalid email message: at least one recipient is required"
+   → Fix: Set message.To with at least one email address
+
+❌ "invalid email message: subject is required"
+   → Fix: Set message.Subject
+
+❌ "invalid email message: body is required"
+   → Fix: Set message.Body
+
+❌ "SMTP authentication failed"
+   → Fix: Check credentials (username/password)
+
+❌ "failed to connect to SMTP server"
+   → Fix: Verify host/port, check firewall, ensure TLS/SSL settings match server
+```
+
+### Async Error Handling
+
+For async sending, errors are logged automatically:
+
+```go
+email.SendAsync(config, message)
+// Errors logged as:
+// [WARN] Failed to send email asynchronously recipients=user@example.com error=...
+```
+
+## Dependencies
+
+### Required
+
+- **Go 1.25+**
+- Standard library: `net/smtp`, `crypto/tls`
+- `github.com/pkg/errors` - Error wrapping with context
+
+### No External SMTP Libraries
+
+This plugin uses Go's standard `net/smtp` library for maximum compatibility and minimal dependencies.
+
+## API Reference
+
+### Types
+
+#### `Config`
+```go
+type Config struct {
+    SMTPHost     string // SMTP server hostname
+    SMTPPort     int    // SMTP server port
+    SMTPUsername string // SMTP auth username
+    SMTPPassword string // SMTP auth password
+    FromEmail    string // From email address
+    FromName     string // From display name (optional)
+    UseTLS       bool   // Enable STARTTLS (port 587)
+    UseSSL       bool   // Enable SSL/TLS (port 465)
+}
+```
+
+#### `Message`
+```go
+type Message struct {
+    To      []string // Recipients
+    Cc      []string // CC recipients (optional)
+    Bcc     []string // BCC recipients (optional)
+    Subject string   // Email subject
+    Body    string   // Email body (plain text or HTML)
+    IsHTML  bool     // true for HTML, false for plain text
+    ReplyTo string   // Reply-To address (optional)
+}
+```
+
+### Functions
+
+#### `Send(config *Config, message *Message) error`
+Sends an email synchronously. Blocks until email is sent or error occurs.
+
+#### `SendAsync(config *Config, message *Message)`
+Sends an email asynchronously in a goroutine. Returns immediately. Errors are logged.
+
+#### `NewClient(config *Config) *Client`
+Creates a new SMTP client for advanced usage.
+
+#### `Client.Send(message *Message) error`
+Sends email using the client's configuration.
+
+## Architecture
+
+```
+plugin/email/
+├── config.go       # SMTP configuration types
+├── message.go      # Email message types and formatting
+├── client.go       # SMTP client implementation
+├── email.go        # High-level Send/SendAsync API
+├── doc.go          # Package documentation
+└── *_test.go       # Unit tests
+```
+
+## License
+
+Part of the Memos project. See main repository for license details.
+
+## Contributing
+
+This plugin follows the Memos contribution guidelines. Please ensure:
+
+1. All code is tested (TDD approach)
+2. Tests pass: `go test ./plugin/email/... -v`
+3. Code is formatted: `go fmt ./plugin/email/...`
+4. No linting errors: `golangci-lint run ./plugin/email/...`
+
+## Support
+
+For issues and questions:
+
+- Memos GitHub Issues: https://github.com/usememos/memos/issues
+- Memos Documentation: https://usememos.com/docs
+
+## Roadmap
+
+Future enhancements may include:
+
+- Email template system
+- Attachment support
+- Inline image embedding
+- Email queuing system
+- Delivery status tracking
+- Bounce handling

plugin/email/client.go

@@ -0,0 +1,143 @@
+package email
+
+import (
+	"crypto/tls"
+	"net/smtp"
+
+	"github.com/pkg/errors"
+)
+
+// Client represents an SMTP email client.
+type Client struct {
+	config *Config
+}
+
+// NewClient creates a new email client with the given configuration.
+func NewClient(config *Config) *Client {
+	return &Client{
+		config: config,
+	}
+}
+
+// validateConfig validates the client configuration.
+func (c *Client) validateConfig() error {
+	if c.config == nil {
+		return errors.New("email configuration is required")
+	}
+	return c.config.Validate()
+}
+
+// createAuth creates an SMTP auth mechanism if credentials are provided.
+func (c *Client) createAuth() smtp.Auth {
+	if c.config.SMTPUsername == "" && c.config.SMTPPassword == "" {
+		return nil
+	}
+	return smtp.PlainAuth("", c.config.SMTPUsername, c.config.SMTPPassword, c.config.SMTPHost)
+}
+
+// createTLSConfig creates a TLS configuration for secure connections.
+func (c *Client) createTLSConfig() *tls.Config {
+	return &tls.Config{
+		ServerName: c.config.SMTPHost,
+		MinVersion: tls.VersionTLS12,
+	}
+}
+
+// Send sends an email message via SMTP.
+func (c *Client) Send(message *Message) error {
+	// Validate configuration
+	if err := c.validateConfig(); err != nil {
+		return errors.Wrap(err, "invalid email configuration")
+	}
+
+	// Validate message
+	if message == nil {
+		return errors.New("message is required")
+	}
+	if err := message.Validate(); err != nil {
+		return errors.Wrap(err, "invalid email message")
+	}
+
+	// Format the message
+	body := message.Format(c.config.FromEmail, c.config.FromName)
+
+	// Get all recipients
+	recipients := message.GetAllRecipients()
+
+	// Create auth
+	auth := c.createAuth()
+
+	// Send based on encryption type
+	if c.config.UseSSL {
+		return c.sendWithSSL(auth, recipients, body)
+	}
+	return c.sendWithTLS(auth, recipients, body)
+}
+
+// sendWithTLS sends email using STARTTLS (port 587).
+func (c *Client) sendWithTLS(auth smtp.Auth, recipients []string, body string) error {
+	serverAddr := c.config.GetServerAddress()
+
+	if c.config.UseTLS {
+		// Use STARTTLS
+		return smtp.SendMail(serverAddr, auth, c.config.FromEmail, recipients, []byte(body))
+	}
+
+	// Send without encryption (not recommended)
+	return smtp.SendMail(serverAddr, auth, c.config.FromEmail, recipients, []byte(body))
+}
+
+// sendWithSSL sends email using SSL/TLS (port 465).
+func (c *Client) sendWithSSL(auth smtp.Auth, recipients []string, body string) error {
+	serverAddr := c.config.GetServerAddress()
+
+	// Create TLS connection
+	tlsConfig := c.createTLSConfig()
+	conn, err := tls.Dial("tcp", serverAddr, tlsConfig)
+	if err != nil {
+		return errors.Wrapf(err, "failed to connect to SMTP server with SSL: %s", serverAddr)
+	}
+	defer conn.Close()
+
+	// Create SMTP client
+	client, err := smtp.NewClient(conn, c.config.SMTPHost)
+	if err != nil {
+		return errors.Wrap(err, "failed to create SMTP client")
+	}
+	defer client.Quit()
+
+	// Authenticate
+	if auth != nil {
+		if err := client.Auth(auth); err != nil {
+			return errors.Wrap(err, "SMTP authentication failed")
+		}
+	}
+
+	// Set sender
+	if err := client.Mail(c.config.FromEmail); err != nil {
+		return errors.Wrap(err, "failed to set sender")
+	}
+
+	// Set recipients
+	for _, recipient := range recipients {
+		if err := client.Rcpt(recipient); err != nil {
+			return errors.Wrapf(err, "failed to set recipient: %s", recipient)
+		}
+	}
+
+	// Send message body
+	writer, err := client.Data()
+	if err != nil {
+		return errors.Wrap(err, "failed to send DATA command")
+	}
+
+	if _, err := writer.Write([]byte(body)); err != nil {
+		return errors.Wrap(err, "failed to write message body")
+	}
+
+	if err := writer.Close(); err != nil {
+		return errors.Wrap(err, "failed to close message writer")
+	}
+
+	return nil
+}

plugin/email/client_test.go

@@ -0,0 +1,121 @@
+package email
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewClient(t *testing.T) {
+	config := &Config{
+		SMTPHost:     "smtp.example.com",
+		SMTPPort:     587,
+		SMTPUsername: "user@example.com",
+		SMTPPassword: "password",
+		FromEmail:    "noreply@example.com",
+		FromName:     "Test App",
+		UseTLS:       true,
+	}
+
+	client := NewClient(config)
+
+	assert.NotNil(t, client)
+	assert.Equal(t, config, client.config)
+}
+
+func TestClientValidateConfig(t *testing.T) {
+	tests := []struct {
+		name    string
+		config  *Config
+		wantErr bool
+	}{
+		{
+			name: "valid config",
+			config: &Config{
+				SMTPHost:  "smtp.example.com",
+				SMTPPort:  587,
+				FromEmail: "test@example.com",
+			},
+			wantErr: false,
+		},
+		{
+			name:    "nil config",
+			config:  nil,
+			wantErr: true,
+		},
+		{
+			name: "invalid config",
+			config: &Config{
+				SMTPHost: "",
+				SMTPPort: 587,
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			client := NewClient(tt.config)
+			err := client.validateConfig()
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestClientSendValidation(t *testing.T) {
+	config := &Config{
+		SMTPHost:  "smtp.example.com",
+		SMTPPort:  587,
+		FromEmail: "test@example.com",
+	}
+	client := NewClient(config)
+
+	tests := []struct {
+		name    string
+		message *Message
+		wantErr bool
+	}{
+		{
+			name: "valid message",
+			message: &Message{
+				To:      []string{"recipient@example.com"},
+				Subject: "Test",
+				Body:    "Test body",
+			},
+			wantErr: false, // Will fail on actual send, but passes validation
+		},
+		{
+			name:    "nil message",
+			message: nil,
+			wantErr: true,
+		},
+		{
+			name: "invalid message",
+			message: &Message{
+				To:      []string{},
+				Subject: "Test",
+				Body:    "Test",
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := client.Send(tt.message)
+			// We expect validation errors for invalid messages
+			// For valid messages, we'll get connection errors (which is expected in tests)
+			if tt.wantErr {
+				assert.Error(t, err)
+				// Should fail validation before attempting connection
+				assert.NotContains(t, err.Error(), "dial")
+			}
+			// Note: We don't assert NoError for valid messages because
+			// we don't have a real SMTP server in tests
+		})
+	}
+}

plugin/email/config.go

@@ -0,0 +1,47 @@
+package email
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+)
+
+// Config represents the SMTP configuration for email sending.
+// These settings should be provided by the self-hosted instance administrator.
+type Config struct {
+	// SMTPHost is the SMTP server hostname (e.g., "smtp.gmail.com")
+	SMTPHost string
+	// SMTPPort is the SMTP server port (common: 587 for TLS, 465 for SSL, 25 for unencrypted)
+	SMTPPort int
+	// SMTPUsername is the SMTP authentication username (usually the email address)
+	SMTPUsername string
+	// SMTPPassword is the SMTP authentication password or app-specific password
+	SMTPPassword string
+	// FromEmail is the email address that will appear in the "From" field
+	FromEmail string
+	// FromName is the display name that will appear in the "From" field
+	FromName string
+	// UseTLS enables STARTTLS encryption (recommended for port 587)
+	UseTLS bool
+	// UseSSL enables SSL/TLS encryption (for port 465)
+	UseSSL bool
+}
+
+// Validate checks if the configuration is valid.
+func (c *Config) Validate() error {
+	if c.SMTPHost == "" {
+		return errors.New("SMTP host is required")
+	}
+	if c.SMTPPort <= 0 || c.SMTPPort > 65535 {
+		return errors.New("SMTP port must be between 1 and 65535")
+	}
+	if c.FromEmail == "" {
+		return errors.New("from email is required")
+	}
+	return nil
+}
+
+// GetServerAddress returns the SMTP server address in the format "host:port".
+func (c *Config) GetServerAddress() string {
+	return fmt.Sprintf("%s:%d", c.SMTPHost, c.SMTPPort)
+}

plugin/email/config_test.go

@@ -0,0 +1,80 @@
+package email
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConfigValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		config  *Config
+		wantErr bool
+	}{
+		{
+			name: "valid config",
+			config: &Config{
+				SMTPHost:     "smtp.gmail.com",
+				SMTPPort:     587,
+				SMTPUsername: "user@example.com",
+				SMTPPassword: "password",
+				FromEmail:    "noreply@example.com",
+				FromName:     "Memos",
+			},
+			wantErr: false,
+		},
+		{
+			name: "missing host",
+			config: &Config{
+				SMTPPort:     587,
+				SMTPUsername: "user@example.com",
+				SMTPPassword: "password",
+				FromEmail:    "noreply@example.com",
+			},
+			wantErr: true,
+		},
+		{
+			name: "invalid port",
+			config: &Config{
+				SMTPHost:     "smtp.gmail.com",
+				SMTPPort:     0,
+				SMTPUsername: "user@example.com",
+				SMTPPassword: "password",
+				FromEmail:    "noreply@example.com",
+			},
+			wantErr: true,
+		},
+		{
+			name: "missing from email",
+			config: &Config{
+				SMTPHost:     "smtp.gmail.com",
+				SMTPPort:     587,
+				SMTPUsername: "user@example.com",
+				SMTPPassword: "password",
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.config.Validate()
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestConfigGetServerAddress(t *testing.T) {
+	config := &Config{
+		SMTPHost: "smtp.gmail.com",
+		SMTPPort: 587,
+	}
+
+	expected := "smtp.gmail.com:587"
+	assert.Equal(t, expected, config.GetServerAddress())
+}

plugin/email/doc.go

@@ -0,0 +1,98 @@
+// Package email provides SMTP email sending functionality for self-hosted Memos instances.
+//
+// This package is designed for self-hosted environments where instance administrators
+// configure their own SMTP servers. It follows industry-standard patterns used by
+// platforms like GitHub, GitLab, and Discourse.
+//
+// # Configuration
+//
+// The package requires SMTP server configuration provided by the instance administrator:
+//
+//	config := &email.Config{
+//	    SMTPHost:     "smtp.gmail.com",
+//	    SMTPPort:     587,
+//	    SMTPUsername: "your-email@gmail.com",
+//	    SMTPPassword: "your-app-password",
+//	    FromEmail:    "noreply@yourdomain.com",
+//	    FromName:     "Memos Notifications",
+//	    UseTLS:       true,
+//	}
+//
+// # Common SMTP Settings
+//
+// Gmail (requires App Password):
+//   - Host: smtp.gmail.com
+//   - Port: 587 (TLS) or 465 (SSL)
+//   - Username: your-email@gmail.com
+//   - UseTLS: true (for port 587) or UseSSL: true (for port 465)
+//
+// SendGrid:
+//   - Host: smtp.sendgrid.net
+//   - Port: 587
+//   - Username: apikey
+//   - Password: your-sendgrid-api-key
+//   - UseTLS: true
+//
+// AWS SES:
+//   - Host: email-smtp.[region].amazonaws.com
+//   - Port: 587
+//   - Username: your-smtp-username
+//   - Password: your-smtp-password
+//   - UseTLS: true
+//
+// Mailgun:
+//   - Host: smtp.mailgun.org
+//   - Port: 587
+//   - Username: your-mailgun-smtp-username
+//   - Password: your-mailgun-smtp-password
+//   - UseTLS: true
+//
+// # Sending Email
+//
+// Synchronous (waits for completion):
+//
+//	message := &email.Message{
+//	    To:      []string{"user@example.com"},
+//	    Subject: "Welcome to Memos",
+//	    Body:    "Thank you for joining!",
+//	    IsHTML:  false,
+//	}
+//
+//	err := email.Send(config, message)
+//	if err != nil {
+//	    // Handle error
+//	}
+//
+// Asynchronous (returns immediately):
+//
+//	email.SendAsync(config, message)
+//	// Errors are logged but not returned
+//
+// # HTML Email
+//
+//	message := &email.Message{
+//	    To:      []string{"user@example.com"},
+//	    Subject: "Welcome!",
+//	    Body:    "<html><body><h1>Welcome to Memos!</h1></body></html>",
+//	    IsHTML:  true,
+//	}
+//
+// # Security Considerations
+//
+//   - Always use TLS (port 587) or SSL (port 465) for production
+//   - Store SMTP credentials securely (environment variables or secrets management)
+//   - Use app-specific passwords for services like Gmail
+//   - Validate and sanitize email content to prevent injection attacks
+//   - Rate limit email sending to prevent abuse
+//
+// # Error Handling
+//
+// The package returns descriptive errors for common issues:
+//   - Configuration validation errors (missing host, invalid port, etc.)
+//   - Message validation errors (missing recipients, subject, or body)
+//   - Connection errors (cannot reach SMTP server)
+//   - Authentication errors (invalid credentials)
+//   - SMTP protocol errors (recipient rejected, etc.)
+//
+// All errors are wrapped with context using github.com/pkg/errors for better debugging.
+package email

plugin/email/email.go

@@ -0,0 +1,43 @@
+package email
+
+import (
+	"log/slog"
+
+	"github.com/pkg/errors"
+)
+
+// Send sends an email synchronously.
+// Returns an error if the email fails to send.
+func Send(config *Config, message *Message) error {
+	if config == nil {
+		return errors.New("email configuration is required")
+	}
+	if message == nil {
+		return errors.New("email message is required")
+	}
+
+	client := NewClient(config)
+	return client.Send(message)
+}
+
+// SendAsync sends an email asynchronously.
+// It spawns a new goroutine to handle the sending and does not wait for the response.
+// Any errors are logged but not returned.
+func SendAsync(config *Config, message *Message) {
+	go func() {
+		if err := Send(config, message); err != nil {
+			// Since we're in a goroutine, we can only log the error
+			recipients := ""
+			if message != nil && len(message.To) > 0 {
+				recipients = message.To[0]
+				if len(message.To) > 1 {
+					recipients += " and others"
+				}
+			}
+
+			slog.Warn("Failed to send email asynchronously",
+				slog.String("recipients", recipients),
+				slog.Any("error", err))
+		}
+	}()
+}

plugin/email/email_test.go

@@ -0,0 +1,127 @@
+package email
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/sync/errgroup"
+)
+
+func TestSend(t *testing.T) {
+	config := &Config{
+		SMTPHost:  "smtp.example.com",
+		SMTPPort:  587,
+		FromEmail: "test@example.com",
+	}
+
+	message := &Message{
+		To:      []string{"recipient@example.com"},
+		Subject: "Test",
+		Body:    "Test body",
+	}
+
+	// This will fail to connect (no real server), but should validate inputs
+	err := Send(config, message)
+	// We expect an error because there's no real SMTP server
+	// But it should be a connection error, not a validation error
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "dial")
+}
+
+func TestSendValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		config  *Config
+		message *Message
+		wantErr bool
+		errMsg  string
+	}{
+		{
+			name:    "nil config",
+			config:  nil,
+			message: &Message{To: []string{"test@example.com"}, Subject: "Test", Body: "Test"},
+			wantErr: true,
+			errMsg:  "configuration is required",
+		},
+		{
+			name:    "nil message",
+			config:  &Config{SMTPHost: "smtp.example.com", SMTPPort: 587, FromEmail: "from@example.com"},
+			message: nil,
+			wantErr: true,
+			errMsg:  "message is required",
+		},
+		{
+			name: "invalid config",
+			config: &Config{
+				SMTPHost: "",
+				SMTPPort: 587,
+			},
+			message: &Message{To: []string{"test@example.com"}, Subject: "Test", Body: "Test"},
+			wantErr: true,
+			errMsg:  "invalid email configuration",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := Send(tt.config, tt.message)
+			if tt.wantErr {
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), tt.errMsg)
+			}
+		})
+	}
+}
+
+func TestSendAsync(t *testing.T) {
+	config := &Config{
+		SMTPHost:  "smtp.example.com",
+		SMTPPort:  587,
+		FromEmail: "test@example.com",
+	}
+
+	message := &Message{
+		To:      []string{"recipient@example.com"},
+		Subject: "Test Async",
+		Body:    "Test async body",
+	}
+
+	// SendAsync should not block
+	start := time.Now()
+	SendAsync(config, message)
+	duration := time.Since(start)
+
+	// Should return almost immediately (< 100ms)
+	assert.Less(t, duration, 100*time.Millisecond)
+
+	// Give goroutine time to start
+	time.Sleep(50 * time.Millisecond)
+}
+
+func TestSendAsyncConcurrent(t *testing.T) {
+	config := &Config{
+		SMTPHost:  "smtp.example.com",
+		SMTPPort:  587,
+		FromEmail: "test@example.com",
+	}
+
+	g := errgroup.Group{}
+	count := 5
+
+	for i := 0; i < count; i++ {
+		g.Go(func() error {
+			message := &Message{
+				To:      []string{"recipient@example.com"},
+				Subject: "Concurrent Test",
+				Body:    "Test body",
+			}
+			SendAsync(config, message)
+			return nil
+		})
+	}
+
+	if err := g.Wait(); err != nil {
+		t.Fatalf("SendAsync calls failed: %v", err)
+	}
+}

plugin/email/message.go

@@ -0,0 +1,91 @@
+package email
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Message represents an email message to be sent.
+type Message struct {
+	To      []string // Required: recipient email addresses
+	Cc      []string // Optional: carbon copy recipients
+	Bcc     []string // Optional: blind carbon copy recipients
+	Subject string   // Required: email subject
+	Body    string   // Required: email body content
+	IsHTML  bool     // Whether the body is HTML (default: false for plain text)
+	ReplyTo string   // Optional: reply-to address
+}
+
+// Validate checks that the message has all required fields.
+func (m *Message) Validate() error {
+	if len(m.To) == 0 {
+		return errors.New("at least one recipient is required")
+	}
+	if m.Subject == "" {
+		return errors.New("subject is required")
+	}
+	if m.Body == "" {
+		return errors.New("body is required")
+	}
+	return nil
+}
+
+// Format creates an RFC 5322 formatted email message.
+func (m *Message) Format(fromEmail, fromName string) string {
+	var sb strings.Builder
+
+	// From header
+	if fromName != "" {
+		sb.WriteString(fmt.Sprintf("From: %s <%s>\r\n", fromName, fromEmail))
+	} else {
+		sb.WriteString(fmt.Sprintf("From: %s\r\n", fromEmail))
+	}
+
+	// To header
+	sb.WriteString(fmt.Sprintf("To: %s\r\n", strings.Join(m.To, ", ")))
+
+	// Cc header (optional)
+	if len(m.Cc) > 0 {
+		sb.WriteString(fmt.Sprintf("Cc: %s\r\n", strings.Join(m.Cc, ", ")))
+	}
+
+	// Reply-To header (optional)
+	if m.ReplyTo != "" {
+		sb.WriteString(fmt.Sprintf("Reply-To: %s\r\n", m.ReplyTo))
+	}
+
+	// Subject header
+	sb.WriteString(fmt.Sprintf("Subject: %s\r\n", m.Subject))
+
+	// Date header (RFC 5322 format)
+	sb.WriteString(fmt.Sprintf("Date: %s\r\n", time.Now().Format(time.RFC1123Z)))
+
+	// MIME headers
+	sb.WriteString("MIME-Version: 1.0\r\n")
+
+	// Content-Type header
+	if m.IsHTML {
+		sb.WriteString("Content-Type: text/html; charset=utf-8\r\n")
+	} else {
+		sb.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
+	}
+
+	// Empty line separating headers from body
+	sb.WriteString("\r\n")
+
+	// Body
+	sb.WriteString(m.Body)
+
+	return sb.String()
+}
+
+// GetAllRecipients returns all recipients (To, Cc, Bcc) as a single slice.
+func (m *Message) GetAllRecipients() []string {
+	var recipients []string
+	recipients = append(recipients, m.To...)
+	recipients = append(recipients, m.Cc...)
+	recipients = append(recipients, m.Bcc...)
+	return recipients
+}

plugin/email/message_test.go

@@ -0,0 +1,181 @@
+package email
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestMessageValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		msg     Message
+		wantErr bool
+	}{
+		{
+			name: "valid message",
+			msg: Message{
+				To:      []string{"user@example.com"},
+				Subject: "Test Subject",
+				Body:    "Test Body",
+			},
+			wantErr: false,
+		},
+		{
+			name: "no recipients",
+			msg: Message{
+				To:      []string{},
+				Subject: "Test Subject",
+				Body:    "Test Body",
+			},
+			wantErr: true,
+		},
+		{
+			name: "no subject",
+			msg: Message{
+				To:      []string{"user@example.com"},
+				Subject: "",
+				Body:    "Test Body",
+			},
+			wantErr: true,
+		},
+		{
+			name: "no body",
+			msg: Message{
+				To:      []string{"user@example.com"},
+				Subject: "Test Subject",
+				Body:    "",
+			},
+			wantErr: true,
+		},
+		{
+			name: "multiple recipients",
+			msg: Message{
+				To:      []string{"user1@example.com", "user2@example.com"},
+				Cc:      []string{"cc@example.com"},
+				Subject: "Test Subject",
+				Body:    "Test Body",
+			},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.msg.Validate()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestMessageFormatPlainText(t *testing.T) {
+	msg := Message{
+		To:      []string{"user@example.com"},
+		Subject: "Test Subject",
+		Body:    "Test Body",
+		IsHTML:  false,
+	}
+
+	formatted := msg.Format("sender@example.com", "Sender Name")
+
+	// Check required headers
+	if !strings.Contains(formatted, "From: Sender Name <sender@example.com>") {
+		t.Error("Missing or incorrect From header")
+	}
+	if !strings.Contains(formatted, "To: user@example.com") {
+		t.Error("Missing or incorrect To header")
+	}
+	if !strings.Contains(formatted, "Subject: Test Subject") {
+		t.Error("Missing or incorrect Subject header")
+	}
+	if !strings.Contains(formatted, "Content-Type: text/plain; charset=utf-8") {
+		t.Error("Missing or incorrect Content-Type header for plain text")
+	}
+	if !strings.Contains(formatted, "Test Body") {
+		t.Error("Missing message body")
+	}
+}
+
+func TestMessageFormatHTML(t *testing.T) {
+	msg := Message{
+		To:      []string{"user@example.com"},
+		Subject: "Test Subject",
+		Body:    "<html><body>Test Body</body></html>",
+		IsHTML:  true,
+	}
+
+	formatted := msg.Format("sender@example.com", "Sender Name")
+
+	// Check HTML content-type
+	if !strings.Contains(formatted, "Content-Type: text/html; charset=utf-8") {
+		t.Error("Missing or incorrect Content-Type header for HTML")
+	}
+	if !strings.Contains(formatted, "<html><body>Test Body</body></html>") {
+		t.Error("Missing HTML body")
+	}
+}
+
+func TestMessageFormatMultipleRecipients(t *testing.T) {
+	msg := Message{
+		To:      []string{"user1@example.com", "user2@example.com"},
+		Cc:      []string{"cc1@example.com", "cc2@example.com"},
+		Bcc:     []string{"bcc@example.com"},
+		Subject: "Test Subject",
+		Body:    "Test Body",
+		ReplyTo: "reply@example.com",
+	}
+
+	formatted := msg.Format("sender@example.com", "Sender Name")
+
+	// Check To header formatting
+	if !strings.Contains(formatted, "To: user1@example.com, user2@example.com") {
+		t.Error("Missing or incorrect To header with multiple recipients")
+	}
+	// Check Cc header formatting
+	if !strings.Contains(formatted, "Cc: cc1@example.com, cc2@example.com") {
+		t.Error("Missing or incorrect Cc header")
+	}
+	// Bcc should NOT appear in the formatted message
+	if strings.Contains(formatted, "Bcc:") {
+		t.Error("Bcc header should not appear in formatted message")
+	}
+	// Check Reply-To header
+	if !strings.Contains(formatted, "Reply-To: reply@example.com") {
+		t.Error("Missing or incorrect Reply-To header")
+	}
+}
+
+func TestGetAllRecipients(t *testing.T) {
+	msg := Message{
+		To:  []string{"user1@example.com", "user2@example.com"},
+		Cc:  []string{"cc@example.com"},
+		Bcc: []string{"bcc@example.com"},
+	}
+
+	recipients := msg.GetAllRecipients()
+
+	// Should have all 4 recipients
+	if len(recipients) != 4 {
+		t.Errorf("GetAllRecipients() returned %d recipients, want 4", len(recipients))
+	}
+
+	// Check all recipients are present
+	expectedRecipients := map[string]bool{
+		"user1@example.com": true,
+		"user2@example.com": true,
+		"cc@example.com":    true,
+		"bcc@example.com":   true,
+	}
+
+	for _, recipient := range recipients {
+		if !expectedRecipients[recipient] {
+			t.Errorf("Unexpected recipient: %s", recipient)
+		}
+		delete(expectedRecipients, recipient)
+	}
+
+	if len(expectedRecipients) > 0 {
+		t.Error("Not all expected recipients were returned")
+	}
+}

plugin/filter/MAINTENANCE.md

@@ -0,0 +1,50 @@
+# Maintaining the Memo Filter Engine
+
+The engine is memo-specific; any future field or behavior changes must stay
+consistent with the memo schema and store implementations. Use this guide when
+extending or debugging the package.
+
+## Adding a New Memo Field
+
+1. **Update the schema**  
+   - Add the field entry in `schema.go`.  
+   - Define the backing column (`Column`), JSON path (if applicable), type, and
+     allowed operators.  
+   - Include the CEL variable in `EnvOptions`.
+2. **Adjust parser or renderer (if needed)**  
+   - For non-scalar fields (JSON booleans, lists), add handling in
+     `parser.go` or extend the renderer helpers.  
+   - Keep validation in the parser (e.g., reject unsupported operators).
+3. **Write a golden test**  
+   - Extend the dialect-specific memo filter tests under
+     `store/db/{sqlite,mysql,postgres}/memo_filter_test.go` with a case that
+     exercises the new field.
+4. **Run `go test ./...`** to ensure the SQL output matches expectations across
+   all dialects.
+
+## Supporting Dialect Nuances
+
+- Centralize differences inside `render.go`. If a new dialect-specific behavior
+  emerges (e.g., JSON operators), add the logic there rather than leaking it
+  into store code.
+- Use the renderer helpers (`jsonExtractExpr`, `jsonArrayExpr`, etc.) rather than
+  sprinkling ad-hoc SQL strings.
+- When placeholders change, adjust `addArg` so that argument numbering stays in
+  sync with store queries.
+
+## Debugging Tips
+
+- **Parser errors** – Most originate in `buildCondition` or schema validation.
+  Enable logging around `parser.go` when diagnosing unknown identifier/operator
+  messages.
+- **Renderer output** – Temporary printf/log statements in `renderCondition` help
+  identify which IR node produced unexpected SQL.
+- **Store integration** – Ensure drivers call `filter.DefaultEngine()` exactly once
+  per process; the singleton caches the parsed CEL environment.
+
+## Testing Checklist
+
+- `go test ./store/...` ensures all dialect tests consume the engine correctly.
+- Add targeted unit tests whenever new IR nodes or renderer paths are introduced.
+- When changing boolean or JSON handling, verify all three dialect test suites
+  (SQLite, MySQL, Postgres) to avoid regression.

plugin/filter/README.md

@@ -0,0 +1,63 @@
+# Memo Filter Engine
+
+This package houses the memo-only filter engine that turns CEL expressions into
+SQL fragments. The engine follows a three phase pipeline inspired by systems
+such as Calcite or Prisma:
+
+1. **Parsing** – CEL expressions are parsed with `cel-go` and validated against
+   the memo-specific environment declared in `schema.go`. Only fields that
+   exist in the schema can surface in the filter.
+2. **Normalization** – the raw CEL AST is converted into an intermediate
+   representation (IR) defined in `ir.go`. The IR is a dialect-agnostic tree of
+   conditions (logical operators, comparisons, list membership, etc.). This
+   step enforces schema rules (e.g. operator compatibility, type checks).
+3. **Rendering** – the renderer in `render.go` walks the IR and produces a SQL
+   fragment plus placeholder arguments tailored to a target dialect
+   (`sqlite`, `mysql`, or `postgres`). Dialect differences such as JSON access,
+   boolean semantics, placeholders, and `LIKE` vs `ILIKE` are encapsulated in
+   renderer helpers.
+
+The entry point is `filter.DefaultEngine()` from `engine.go`. It lazily constructs
+an `Engine` configured with the memo schema and exposes:
+
+```go
+engine, _ := filter.DefaultEngine()
+stmt, _ := engine.CompileToStatement(ctx, `has_task_list && visibility == "PUBLIC"`, filter.RenderOptions{
+	Dialect: filter.DialectPostgres,
+})
+// stmt.SQL  -> "((memo.payload->'property'->>'hasTaskList')::boolean IS TRUE AND memo.visibility = $1)"
+// stmt.Args -> ["PUBLIC"]
+```
+
+## Core Files
+
+| File          | Responsibility                                                                  |
+| ------------- | ------------------------------------------------------------------------------- |
+| `schema.go`   | Declares memo fields, their types, backing columns, CEL environment options     |
+| `ir.go`       | IR node definitions used across the pipeline                                    |
+| `parser.go`   | Converts CEL `Expr` into IR while applying schema validation                    |
+| `render.go`   | Translates IR into SQL, handling dialect-specific behavior                      |
+| `engine.go`   | Glue between the phases; exposes `Compile`, `CompileToStatement`, and `DefaultEngine` |
+| `helpers.go`  | Convenience helpers for store integration (appending conditions)                |
+
+## SQL Generation Notes
+
+- **Placeholders** — `?` is used for SQLite/MySQL, `$n` for Postgres. The renderer
+  tracks offsets to compose queries with pre-existing arguments.
+- **JSON Fields** — Memo metadata lives in `memo.payload`. The renderer handles
+  `JSON_EXTRACT`/`json_extract`/`->`/`->>` variations and boolean coercion.
+- **Tag Operations** — `tag in [...]` and `"tag" in tags` become JSON array
+  predicates. SQLite uses `LIKE` patterns, MySQL uses `JSON_CONTAINS`, and
+  Postgres uses `@>`.
+- **Boolean Flags** — Fields such as `has_task_list` render as `IS TRUE` equality
+  checks, or comparisons against `CAST('true' AS JSON)` depending on the dialect.
+
+## Typical Integration
+
+1. Fetch the engine with `filter.DefaultEngine()`.
+2. Call `CompileToStatement` using the appropriate dialect enum.
+3. Append the emitted SQL fragment/args to the existing `WHERE` clause.
+4. Execute the resulting query through the store driver.
+
+The `helpers.AppendConditions` helper encapsulates steps 2–3 when a driver needs
+to process an array of filters.

plugin/filter/engine.go

@@ -0,0 +1,191 @@
+package filter
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+
+	"github.com/google/cel-go/cel"
+	"github.com/pkg/errors"
+)
+
+// Engine parses CEL filters into a dialect-agnostic condition tree.
+type Engine struct {
+	schema Schema
+	env    *cel.Env
+}
+
+// NewEngine builds a new Engine for the provided schema.
+func NewEngine(schema Schema) (*Engine, error) {
+	env, err := cel.NewEnv(schema.EnvOptions...)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create CEL environment")
+	}
+	return &Engine{
+		schema: schema,
+		env:    env,
+	}, nil
+}
+
+// Program stores a compiled filter condition.
+type Program struct {
+	schema    Schema
+	condition Condition
+}
+
+// ConditionTree exposes the underlying condition tree.
+func (p *Program) ConditionTree() Condition {
+	return p.condition
+}
+
+// Compile parses the filter string into an executable program.
+func (e *Engine) Compile(_ context.Context, filter string) (*Program, error) {
+	if strings.TrimSpace(filter) == "" {
+		return nil, errors.New("filter expression is empty")
+	}
+
+	filter = normalizeLegacyFilter(filter)
+
+	ast, issues := e.env.Compile(filter)
+	if issues != nil && issues.Err() != nil {
+		return nil, errors.Wrap(issues.Err(), "failed to compile filter")
+	}
+	parsed, err := cel.AstToParsedExpr(ast)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to convert AST")
+	}
+
+	cond, err := buildCondition(parsed.GetExpr(), e.schema)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Program{
+		schema:    e.schema,
+		condition: cond,
+	}, nil
+}
+
+// CompileToStatement compiles and renders the filter in a single step.
+func (e *Engine) CompileToStatement(ctx context.Context, filter string, opts RenderOptions) (Statement, error) {
+	program, err := e.Compile(ctx, filter)
+	if err != nil {
+		return Statement{}, err
+	}
+	return program.Render(opts)
+}
+
+// RenderOptions configure SQL rendering.
+type RenderOptions struct {
+	Dialect           DialectName
+	PlaceholderOffset int
+	DisableNullChecks bool
+}
+
+// Statement contains the rendered SQL fragment and its args.
+type Statement struct {
+	SQL  string
+	Args []any
+}
+
+// Render converts the program into a dialect-specific SQL fragment.
+func (p *Program) Render(opts RenderOptions) (Statement, error) {
+	renderer := newRenderer(p.schema, opts)
+	return renderer.Render(p.condition)
+}
+
+var (
+	defaultOnce           sync.Once
+	defaultInst           *Engine
+	defaultErr            error
+	defaultAttachmentOnce sync.Once
+	defaultAttachmentInst *Engine
+	defaultAttachmentErr  error
+)
+
+// DefaultEngine returns the process-wide memo filter engine.
+func DefaultEngine() (*Engine, error) {
+	defaultOnce.Do(func() {
+		defaultInst, defaultErr = NewEngine(NewSchema())
+	})
+	return defaultInst, defaultErr
+}
+
+// DefaultAttachmentEngine returns the process-wide attachment filter engine.
+func DefaultAttachmentEngine() (*Engine, error) {
+	defaultAttachmentOnce.Do(func() {
+		defaultAttachmentInst, defaultAttachmentErr = NewEngine(NewAttachmentSchema())
+	})
+	return defaultAttachmentInst, defaultAttachmentErr
+}
+
+func normalizeLegacyFilter(expr string) string {
+	expr = rewriteNumericLogicalOperand(expr, "&&")
+	expr = rewriteNumericLogicalOperand(expr, "||")
+	return expr
+}
+
+func rewriteNumericLogicalOperand(expr, op string) string {
+	var builder strings.Builder
+	n := len(expr)
+	i := 0
+	var inQuote rune
+
+	for i < n {
+		ch := expr[i]
+
+		if inQuote != 0 {
+			builder.WriteByte(ch)
+			if ch == '\\' && i+1 < n {
+				builder.WriteByte(expr[i+1])
+				i += 2
+				continue
+			}
+			if ch == byte(inQuote) {
+				inQuote = 0
+			}
+			i++
+			continue
+		}
+
+		if ch == '\'' || ch == '"' {
+			inQuote = rune(ch)
+			builder.WriteByte(ch)
+			i++
+			continue
+		}
+
+		if strings.HasPrefix(expr[i:], op) {
+			builder.WriteString(op)
+			i += len(op)
+
+			// Preserve whitespace following the operator.
+			wsStart := i
+			for i < n && (expr[i] == ' ' || expr[i] == '\t') {
+				i++
+			}
+			builder.WriteString(expr[wsStart:i])
+
+			signStart := i
+			if i < n && (expr[i] == '+' || expr[i] == '-') {
+				i++
+			}
+			for i < n && expr[i] >= '0' && expr[i] <= '9' {
+				i++
+			}
+			if i > signStart {
+				numLiteral := expr[signStart:i]
+				builder.WriteString(fmt.Sprintf("(%s != 0)", numLiteral))
+			} else {
+				builder.WriteString(expr[signStart:i])
+			}
+			continue
+		}
+
+		builder.WriteByte(ch)
+		i++
+	}
+
+	return builder.String()
+}

plugin/filter/helpers.go

@@ -0,0 +1,25 @@
+package filter
+
+import (
+	"context"
+	"fmt"
+)
+
+// AppendConditions compiles the provided filters and appends the resulting SQL fragments and args.
+func AppendConditions(ctx context.Context, engine *Engine, filters []string, dialect DialectName, where *[]string, args *[]any) error {
+	for _, filterStr := range filters {
+		stmt, err := engine.CompileToStatement(ctx, filterStr, RenderOptions{
+			Dialect:           dialect,
+			PlaceholderOffset: len(*args),
+		})
+		if err != nil {
+			return err
+		}
+		if stmt.SQL == "" {
+			continue
+		}
+		*where = append(*where, fmt.Sprintf("(%s)", stmt.SQL))
+		*args = append(*args, stmt.Args...)
+	}
+	return nil
+}

plugin/filter/ir.go

@@ -0,0 +1,159 @@
+package filter
+
+// Condition represents a boolean expression derived from the CEL filter.
+type Condition interface {
+	isCondition()
+}
+
+// LogicalOperator enumerates the supported logical operators.
+type LogicalOperator string
+
+const (
+	LogicalAnd LogicalOperator = "AND"
+	LogicalOr  LogicalOperator = "OR"
+)
+
+// LogicalCondition composes two conditions with a logical operator.
+type LogicalCondition struct {
+	Operator LogicalOperator
+	Left     Condition
+	Right    Condition
+}
+
+func (*LogicalCondition) isCondition() {}
+
+// NotCondition negates a child condition.
+type NotCondition struct {
+	Expr Condition
+}
+
+func (*NotCondition) isCondition() {}
+
+// FieldPredicateCondition asserts that a field evaluates to true.
+type FieldPredicateCondition struct {
+	Field string
+}
+
+func (*FieldPredicateCondition) isCondition() {}
+
+// ComparisonOperator lists supported comparison operators.
+type ComparisonOperator string
+
+const (
+	CompareEq  ComparisonOperator = "="
+	CompareNeq ComparisonOperator = "!="
+	CompareLt  ComparisonOperator = "<"
+	CompareLte ComparisonOperator = "<="
+	CompareGt  ComparisonOperator = ">"
+	CompareGte ComparisonOperator = ">="
+)
+
+// ComparisonCondition represents a binary comparison.
+type ComparisonCondition struct {
+	Left     ValueExpr
+	Operator ComparisonOperator
+	Right    ValueExpr
+}
+
+func (*ComparisonCondition) isCondition() {}
+
+// InCondition represents an IN predicate with literal list values.
+type InCondition struct {
+	Left   ValueExpr
+	Values []ValueExpr
+}
+
+func (*InCondition) isCondition() {}
+
+// ElementInCondition represents the CEL syntax `"value" in field`.
+type ElementInCondition struct {
+	Element ValueExpr
+	Field   string
+}
+
+func (*ElementInCondition) isCondition() {}
+
+// ContainsCondition models the <field>.contains(<value>) call.
+type ContainsCondition struct {
+	Field string
+	Value string
+}
+
+func (*ContainsCondition) isCondition() {}
+
+// ConstantCondition captures a literal boolean outcome.
+type ConstantCondition struct {
+	Value bool
+}
+
+func (*ConstantCondition) isCondition() {}
+
+// ValueExpr models arithmetic or scalar expressions whose result feeds a comparison.
+type ValueExpr interface {
+	isValueExpr()
+}
+
+// FieldRef references a named schema field.
+type FieldRef struct {
+	Name string
+}
+
+func (*FieldRef) isValueExpr() {}
+
+// LiteralValue holds a literal scalar.
+type LiteralValue struct {
+	Value interface{}
+}
+
+func (*LiteralValue) isValueExpr() {}
+
+// FunctionValue captures simple function calls like size(tags).
+type FunctionValue struct {
+	Name string
+	Args []ValueExpr
+}
+
+func (*FunctionValue) isValueExpr() {}
+
+// ListComprehensionCondition represents CEL macros like exists(), all(), filter().
+type ListComprehensionCondition struct {
+	Kind      ComprehensionKind
+	Field     string        // The list field to iterate over (e.g., "tags")
+	IterVar   string        // The iteration variable name (e.g., "t")
+	Predicate PredicateExpr // The predicate to evaluate for each element
+}
+
+func (*ListComprehensionCondition) isCondition() {}
+
+// ComprehensionKind enumerates the types of list comprehensions.
+type ComprehensionKind string
+
+const (
+	ComprehensionExists ComprehensionKind = "exists"
+)
+
+// PredicateExpr represents predicates used in comprehensions.
+type PredicateExpr interface {
+	isPredicateExpr()
+}
+
+// StartsWithPredicate represents t.startsWith("prefix").
+type StartsWithPredicate struct {
+	Prefix string
+}
+
+func (*StartsWithPredicate) isPredicateExpr() {}
+
+// EndsWithPredicate represents t.endsWith("suffix").
+type EndsWithPredicate struct {
+	Suffix string
+}
+
+func (*EndsWithPredicate) isPredicateExpr() {}
+
+// ContainsPredicate represents t.contains("substring").
+type ContainsPredicate struct {
+	Substring string
+}
+
+func (*ContainsPredicate) isPredicateExpr() {}

plugin/filter/parser.go

@@ -0,0 +1,586 @@
+package filter
+
+import (
+	"time"
+
+	"github.com/pkg/errors"
+	exprv1 "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
+)
+
+func buildCondition(expr *exprv1.Expr, schema Schema) (Condition, error) {
+	switch v := expr.ExprKind.(type) {
+	case *exprv1.Expr_CallExpr:
+		return buildCallCondition(v.CallExpr, schema)
+	case *exprv1.Expr_ConstExpr:
+		val, err := getConstValue(expr)
+		if err != nil {
+			return nil, err
+		}
+		switch v := val.(type) {
+		case bool:
+			return &ConstantCondition{Value: v}, nil
+		case int64:
+			return &ConstantCondition{Value: v != 0}, nil
+		case float64:
+			return &ConstantCondition{Value: v != 0}, nil
+		default:
+			return nil, errors.New("filter must evaluate to a boolean value")
+		}
+	case *exprv1.Expr_IdentExpr:
+		name := v.IdentExpr.GetName()
+		field, ok := schema.Field(name)
+		if !ok {
+			return nil, errors.Errorf("unknown identifier %q", name)
+		}
+		if field.Type != FieldTypeBool {
+			return nil, errors.Errorf("identifier %q is not boolean", name)
+		}
+		return &FieldPredicateCondition{Field: name}, nil
+	case *exprv1.Expr_ComprehensionExpr:
+		return buildComprehensionCondition(v.ComprehensionExpr, schema)
+	default:
+		return nil, errors.New("unsupported top-level expression")
+	}
+}
+
+func buildCallCondition(call *exprv1.Expr_Call, schema Schema) (Condition, error) {
+	switch call.Function {
+	case "_&&_":
+		if len(call.Args) != 2 {
+			return nil, errors.New("logical AND expects two arguments")
+		}
+		left, err := buildCondition(call.Args[0], schema)
+		if err != nil {
+			return nil, err
+		}
+		right, err := buildCondition(call.Args[1], schema)
+		if err != nil {
+			return nil, err
+		}
+		return &LogicalCondition{
+			Operator: LogicalAnd,
+			Left:     left,
+			Right:    right,
+		}, nil
+	case "_||_":
+		if len(call.Args) != 2 {
+			return nil, errors.New("logical OR expects two arguments")
+		}
+		left, err := buildCondition(call.Args[0], schema)
+		if err != nil {
+			return nil, err
+		}
+		right, err := buildCondition(call.Args[1], schema)
+		if err != nil {
+			return nil, err
+		}
+		return &LogicalCondition{
+			Operator: LogicalOr,
+			Left:     left,
+			Right:    right,
+		}, nil
+	case "!_":
+		if len(call.Args) != 1 {
+			return nil, errors.New("logical NOT expects one argument")
+		}
+		child, err := buildCondition(call.Args[0], schema)
+		if err != nil {
+			return nil, err
+		}
+		return &NotCondition{Expr: child}, nil
+	case "_==_", "_!=_", "_<_", "_>_", "_<=_", "_>=_":
+		return buildComparisonCondition(call, schema)
+	case "@in":
+		return buildInCondition(call, schema)
+	case "contains":
+		return buildContainsCondition(call, schema)
+	default:
+		val, ok, err := evaluateBool(call)
+		if err != nil {
+			return nil, err
+		}
+		if ok {
+			return &ConstantCondition{Value: val}, nil
+		}
+		return nil, errors.Errorf("unsupported call expression %q", call.Function)
+	}
+}
+
+func buildComparisonCondition(call *exprv1.Expr_Call, schema Schema) (Condition, error) {
+	if len(call.Args) != 2 {
+		return nil, errors.New("comparison expects two arguments")
+	}
+	op, err := toComparisonOperator(call.Function)
+	if err != nil {
+		return nil, err
+	}
+
+	left, err := buildValueExpr(call.Args[0], schema)
+	if err != nil {
+		return nil, err
+	}
+	right, err := buildValueExpr(call.Args[1], schema)
+	if err != nil {
+		return nil, err
+	}
+
+	// If the left side is a field, validate allowed operators.
+	if field, ok := left.(*FieldRef); ok {
+		def, exists := schema.Field(field.Name)
+		if !exists {
+			return nil, errors.Errorf("unknown identifier %q", field.Name)
+		}
+		if def.Kind == FieldKindVirtualAlias {
+			def, exists = schema.ResolveAlias(field.Name)
+			if !exists {
+				return nil, errors.Errorf("invalid alias %q", field.Name)
+			}
+		}
+		if def.AllowedComparisonOps != nil {
+			if _, allowed := def.AllowedComparisonOps[op]; !allowed {
+				return nil, errors.Errorf("operator %s not allowed for field %q", op, field.Name)
+			}
+		}
+	}
+
+	return &ComparisonCondition{
+		Left:     left,
+		Operator: op,
+		Right:    right,
+	}, nil
+}
+
+func buildInCondition(call *exprv1.Expr_Call, schema Schema) (Condition, error) {
+	if len(call.Args) != 2 {
+		return nil, errors.New("in operator expects two arguments")
+	}
+
+	// Handle identifier in list syntax.
+	if identName, err := getIdentName(call.Args[0]); err == nil {
+		if field, ok := schema.Field(identName); ok && field.Kind == FieldKindVirtualAlias {
+			if _, aliasOk := schema.ResolveAlias(identName); !aliasOk {
+				return nil, errors.Errorf("invalid alias %q", identName)
+			}
+		} else if !ok {
+			return nil, errors.Errorf("unknown identifier %q", identName)
+		}
+
+		if listExpr := call.Args[1].GetListExpr(); listExpr != nil {
+			values := make([]ValueExpr, 0, len(listExpr.Elements))
+			for _, element := range listExpr.Elements {
+				value, err := buildValueExpr(element, schema)
+				if err != nil {
+					return nil, err
+				}
+				values = append(values, value)
+			}
+			return &InCondition{
+				Left:   &FieldRef{Name: identName},
+				Values: values,
+			}, nil
+		}
+	}
+
+	// Handle "value in identifier" syntax.
+	if identName, err := getIdentName(call.Args[1]); err == nil {
+		if _, ok := schema.Field(identName); !ok {
+			return nil, errors.Errorf("unknown identifier %q", identName)
+		}
+		element, err := buildValueExpr(call.Args[0], schema)
+		if err != nil {
+			return nil, err
+		}
+		return &ElementInCondition{
+			Element: element,
+			Field:   identName,
+		}, nil
+	}
+
+	return nil, errors.New("invalid use of in operator")
+}
+
+func buildContainsCondition(call *exprv1.Expr_Call, schema Schema) (Condition, error) {
+	if call.Target == nil {
+		return nil, errors.New("contains requires a target")
+	}
+	targetName, err := getIdentName(call.Target)
+	if err != nil {
+		return nil, err
+	}
+
+	field, ok := schema.Field(targetName)
+	if !ok {
+		return nil, errors.Errorf("unknown identifier %q", targetName)
+	}
+	if !field.SupportsContains {
+		return nil, errors.Errorf("identifier %q does not support contains()", targetName)
+	}
+	if len(call.Args) != 1 {
+		return nil, errors.New("contains expects exactly one argument")
+	}
+	value, err := getConstValue(call.Args[0])
+	if err != nil {
+		return nil, errors.Wrap(err, "contains only supports literal arguments")
+	}
+	str, ok := value.(string)
+	if !ok {
+		return nil, errors.New("contains argument must be a string")
+	}
+	return &ContainsCondition{
+		Field: targetName,
+		Value: str,
+	}, nil
+}
+
+func buildValueExpr(expr *exprv1.Expr, schema Schema) (ValueExpr, error) {
+	if identName, err := getIdentName(expr); err == nil {
+		if _, ok := schema.Field(identName); !ok {
+			return nil, errors.Errorf("unknown identifier %q", identName)
+		}
+		return &FieldRef{Name: identName}, nil
+	}
+
+	if literal, err := getConstValue(expr); err == nil {
+		return &LiteralValue{Value: literal}, nil
+	}
+
+	if value, ok, err := evaluateNumeric(expr); err != nil {
+		return nil, err
+	} else if ok {
+		return &LiteralValue{Value: value}, nil
+	}
+
+	if boolVal, ok, err := evaluateBoolExpr(expr); err != nil {
+		return nil, err
+	} else if ok {
+		return &LiteralValue{Value: boolVal}, nil
+	}
+
+	if call := expr.GetCallExpr(); call != nil {
+		switch call.Function {
+		case "size":
+			if len(call.Args) != 1 {
+				return nil, errors.New("size() expects one argument")
+			}
+			arg, err := buildValueExpr(call.Args[0], schema)
+			if err != nil {
+				return nil, err
+			}
+			return &FunctionValue{
+				Name: "size",
+				Args: []ValueExpr{arg},
+			}, nil
+		case "now":
+			return &LiteralValue{Value: timeNowUnix()}, nil
+		case "_+_", "_-_", "_*_":
+			value, ok, err := evaluateNumeric(expr)
+			if err != nil {
+				return nil, err
+			}
+			if ok {
+				return &LiteralValue{Value: value}, nil
+			}
+		default:
+			// Fall through to error return below
+		}
+	}
+
+	return nil, errors.New("unsupported value expression")
+}
+
+func toComparisonOperator(fn string) (ComparisonOperator, error) {
+	switch fn {
+	case "_==_":
+		return CompareEq, nil
+	case "_!=_":
+		return CompareNeq, nil
+	case "_<_":
+		return CompareLt, nil
+	case "_>_":
+		return CompareGt, nil
+	case "_<=_":
+		return CompareLte, nil
+	case "_>=_":
+		return CompareGte, nil
+	default:
+		return "", errors.Errorf("unsupported comparison operator %q", fn)
+	}
+}
+
+func getIdentName(expr *exprv1.Expr) (string, error) {
+	if ident := expr.GetIdentExpr(); ident != nil {
+		return ident.GetName(), nil
+	}
+	return "", errors.New("expression is not an identifier")
+}
+
+func getConstValue(expr *exprv1.Expr) (interface{}, error) {
+	v, ok := expr.ExprKind.(*exprv1.Expr_ConstExpr)
+	if !ok {
+		return nil, errors.New("expression is not a literal")
+	}
+	switch x := v.ConstExpr.ConstantKind.(type) {
+	case *exprv1.Constant_StringValue:
+		return v.ConstExpr.GetStringValue(), nil
+	case *exprv1.Constant_Int64Value:
+		return v.ConstExpr.GetInt64Value(), nil
+	case *exprv1.Constant_Uint64Value:
+		return int64(v.ConstExpr.GetUint64Value()), nil
+	case *exprv1.Constant_DoubleValue:
+		return v.ConstExpr.GetDoubleValue(), nil
+	case *exprv1.Constant_BoolValue:
+		return v.ConstExpr.GetBoolValue(), nil
+	case *exprv1.Constant_NullValue:
+		return nil, nil
+	default:
+		return nil, errors.Errorf("unsupported constant %T", x)
+	}
+}
+
+func evaluateBool(call *exprv1.Expr_Call) (bool, bool, error) {
+	val, ok, err := evaluateBoolExpr(&exprv1.Expr{ExprKind: &exprv1.Expr_CallExpr{CallExpr: call}})
+	return val, ok, err
+}
+
+func evaluateBoolExpr(expr *exprv1.Expr) (bool, bool, error) {
+	if literal, err := getConstValue(expr); err == nil {
+		if b, ok := literal.(bool); ok {
+			return b, true, nil
+		}
+		return false, false, nil
+	}
+	if call := expr.GetCallExpr(); call != nil && call.Function == "!_" {
+		if len(call.Args) != 1 {
+			return false, false, errors.New("NOT expects exactly one argument")
+		}
+		val, ok, err := evaluateBoolExpr(call.Args[0])
+		if err != nil || !ok {
+			return false, false, err
+		}
+		return !val, true, nil
+	}
+	return false, false, nil
+}
+
+func evaluateNumeric(expr *exprv1.Expr) (int64, bool, error) {
+	if literal, err := getConstValue(expr); err == nil {
+		switch v := literal.(type) {
+		case int64:
+			return v, true, nil
+		case float64:
+			return int64(v), true, nil
+		}
+		return 0, false, nil
+	}
+
+	call := expr.GetCallExpr()
+	if call == nil {
+		return 0, false, nil
+	}
+
+	switch call.Function {
+	case "now":
+		return timeNowUnix(), true, nil
+	case "_+_", "_-_", "_*_":
+		if len(call.Args) != 2 {
+			return 0, false, errors.New("arithmetic requires two arguments")
+		}
+		left, ok, err := evaluateNumeric(call.Args[0])
+		if err != nil {
+			return 0, false, err
+		}
+		if !ok {
+			return 0, false, nil
+		}
+		right, ok, err := evaluateNumeric(call.Args[1])
+		if err != nil {
+			return 0, false, err
+		}
+		if !ok {
+			return 0, false, nil
+		}
+		switch call.Function {
+		case "_+_":
+			return left + right, true, nil
+		case "_-_":
+			return left - right, true, nil
+		case "_*_":
+			return left * right, true, nil
+		default:
+			return 0, false, errors.Errorf("unsupported arithmetic operator %q", call.Function)
+		}
+	default:
+		return 0, false, nil
+	}
+}
+
+func timeNowUnix() int64 {
+	return time.Now().Unix()
+}
+
+// buildComprehensionCondition handles CEL comprehension expressions (exists, all, etc.).
+func buildComprehensionCondition(comp *exprv1.Expr_Comprehension, schema Schema) (Condition, error) {
+	// Determine the comprehension kind by examining the loop initialization and step
+	kind, err := detectComprehensionKind(comp)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get the field being iterated over
+	iterRangeIdent := comp.IterRange.GetIdentExpr()
+	if iterRangeIdent == nil {
+		return nil, errors.New("comprehension range must be a field identifier")
+	}
+	fieldName := iterRangeIdent.GetName()
+
+	// Validate the field
+	field, ok := schema.Field(fieldName)
+	if !ok {
+		return nil, errors.Errorf("unknown field %q in comprehension", fieldName)
+	}
+	if field.Kind != FieldKindJSONList {
+		return nil, errors.Errorf("field %q does not support comprehension (must be a list)", fieldName)
+	}
+
+	// Extract the predicate from the loop step
+	predicate, err := extractPredicate(comp, schema)
+	if err != nil {
+		return nil, err
+	}
+
+	return &ListComprehensionCondition{
+		Kind:      kind,
+		Field:     fieldName,
+		IterVar:   comp.IterVar,
+		Predicate: predicate,
+	}, nil
+}
+
+// detectComprehensionKind determines if this is an exists() macro.
+// Only exists() is currently supported.
+func detectComprehensionKind(comp *exprv1.Expr_Comprehension) (ComprehensionKind, error) {
+	// Check the accumulator initialization
+	accuInit := comp.AccuInit.GetConstExpr()
+	if accuInit == nil {
+		return "", errors.New("comprehension accumulator must be initialized with a constant")
+	}
+
+	// exists() starts with false and uses OR (||) in loop step
+	if !accuInit.GetBoolValue() {
+		if step := comp.LoopStep.GetCallExpr(); step != nil && step.Function == "_||_" {
+			return ComprehensionExists, nil
+		}
+	}
+
+	// all() starts with true and uses AND (&&) - not supported
+	if accuInit.GetBoolValue() {
+		if step := comp.LoopStep.GetCallExpr(); step != nil && step.Function == "_&&_" {
+			return "", errors.New("all() comprehension is not supported; use exists() instead")
+		}
+	}
+
+	return "", errors.New("unsupported comprehension type; only exists() is supported")
+}
+
+// extractPredicate extracts the predicate expression from the comprehension loop step.
+func extractPredicate(comp *exprv1.Expr_Comprehension, _ Schema) (PredicateExpr, error) {
+	// The loop step is: @result || predicate(t) for exists
+	//                or: @result && predicate(t) for all
+	step := comp.LoopStep.GetCallExpr()
+	if step == nil {
+		return nil, errors.New("comprehension loop step must be a call expression")
+	}
+
+	if len(step.Args) != 2 {
+		return nil, errors.New("comprehension loop step must have two arguments")
+	}
+
+	// The predicate is the second argument
+	predicateExpr := step.Args[1]
+	predicateCall := predicateExpr.GetCallExpr()
+	if predicateCall == nil {
+		return nil, errors.New("comprehension predicate must be a function call")
+	}
+
+	// Handle different predicate functions
+	switch predicateCall.Function {
+	case "startsWith":
+		return buildStartsWithPredicate(predicateCall, comp.IterVar)
+	case "endsWith":
+		return buildEndsWithPredicate(predicateCall, comp.IterVar)
+	case "contains":
+		return buildContainsPredicate(predicateCall, comp.IterVar)
+	default:
+		return nil, errors.Errorf("unsupported predicate function %q in comprehension (supported: startsWith, endsWith, contains)", predicateCall.Function)
+	}
+}
+
+// buildStartsWithPredicate extracts the pattern from t.startsWith("prefix").
+func buildStartsWithPredicate(call *exprv1.Expr_Call, iterVar string) (PredicateExpr, error) {
+	// Verify the target is the iteration variable
+	if target := call.Target.GetIdentExpr(); target == nil || target.GetName() != iterVar {
+		return nil, errors.Errorf("startsWith target must be the iteration variable %q", iterVar)
+	}
+
+	if len(call.Args) != 1 {
+		return nil, errors.New("startsWith expects exactly one argument")
+	}
+
+	prefix, err := getConstValue(call.Args[0])
+	if err != nil {
+		return nil, errors.Wrap(err, "startsWith argument must be a constant string")
+	}
+
+	prefixStr, ok := prefix.(string)
+	if !ok {
+		return nil, errors.New("startsWith argument must be a string")
+	}
+
+	return &StartsWithPredicate{Prefix: prefixStr}, nil
+}
+
+// buildEndsWithPredicate extracts the pattern from t.endsWith("suffix").
+func buildEndsWithPredicate(call *exprv1.Expr_Call, iterVar string) (PredicateExpr, error) {
+	if target := call.Target.GetIdentExpr(); target == nil || target.GetName() != iterVar {
+		return nil, errors.Errorf("endsWith target must be the iteration variable %q", iterVar)
+	}
+
+	if len(call.Args) != 1 {
+		return nil, errors.New("endsWith expects exactly one argument")
+	}
+
+	suffix, err := getConstValue(call.Args[0])
+	if err != nil {
+		return nil, errors.Wrap(err, "endsWith argument must be a constant string")
+	}
+
+	suffixStr, ok := suffix.(string)
+	if !ok {
+		return nil, errors.New("endsWith argument must be a string")
+	}
+
+	return &EndsWithPredicate{Suffix: suffixStr}, nil
+}
+
+// buildContainsPredicate extracts the pattern from t.contains("substring").
+func buildContainsPredicate(call *exprv1.Expr_Call, iterVar string) (PredicateExpr, error) {
+	if target := call.Target.GetIdentExpr(); target == nil || target.GetName() != iterVar {
+		return nil, errors.Errorf("contains target must be the iteration variable %q", iterVar)
+	}
+
+	if len(call.Args) != 1 {
+		return nil, errors.New("contains expects exactly one argument")
+	}
+
+	substring, err := getConstValue(call.Args[0])
+	if err != nil {
+		return nil, errors.Wrap(err, "contains argument must be a constant string")
+	}
+
+	substringStr, ok := substring.(string)
+	if !ok {
+		return nil, errors.New("contains argument must be a string")
+	}
+
+	return &ContainsPredicate{Substring: substringStr}, nil
+}

plugin/filter/render.go

@@ -0,0 +1,748 @@
+package filter
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+type renderer struct {
+	schema             Schema
+	dialect            DialectName
+	placeholderOffset  int
+	placeholderCounter int
+	args               []any
+}
+
+type renderResult struct {
+	sql           string
+	trivial       bool
+	unsatisfiable bool
+}
+
+func newRenderer(schema Schema, opts RenderOptions) *renderer {
+	return &renderer{
+		schema:            schema,
+		dialect:           opts.Dialect,
+		placeholderOffset: opts.PlaceholderOffset,
+	}
+}
+
+func (r *renderer) Render(cond Condition) (Statement, error) {
+	result, err := r.renderCondition(cond)
+	if err != nil {
+		return Statement{}, err
+	}
+	args := r.args
+	if args == nil {
+		args = []any{}
+	}
+
+	switch {
+	case result.unsatisfiable:
+		return Statement{
+			SQL:  "1 = 0",
+			Args: args,
+		}, nil
+	case result.trivial:
+		return Statement{
+			SQL:  "",
+			Args: args,
+		}, nil
+	default:
+		return Statement{
+			SQL:  result.sql,
+			Args: args,
+		}, nil
+	}
+}
+
+func (r *renderer) renderCondition(cond Condition) (renderResult, error) {
+	switch c := cond.(type) {
+	case *LogicalCondition:
+		return r.renderLogicalCondition(c)
+	case *NotCondition:
+		return r.renderNotCondition(c)
+	case *FieldPredicateCondition:
+		return r.renderFieldPredicate(c)
+	case *ComparisonCondition:
+		return r.renderComparison(c)
+	case *InCondition:
+		return r.renderInCondition(c)
+	case *ElementInCondition:
+		return r.renderElementInCondition(c)
+	case *ContainsCondition:
+		return r.renderContainsCondition(c)
+	case *ListComprehensionCondition:
+		return r.renderListComprehension(c)
+	case *ConstantCondition:
+		if c.Value {
+			return renderResult{trivial: true}, nil
+		}
+		return renderResult{sql: "1 = 0", unsatisfiable: true}, nil
+	default:
+		return renderResult{}, errors.Errorf("unsupported condition type %T", c)
+	}
+}
+
+func (r *renderer) renderLogicalCondition(cond *LogicalCondition) (renderResult, error) {
+	left, err := r.renderCondition(cond.Left)
+	if err != nil {
+		return renderResult{}, err
+	}
+	right, err := r.renderCondition(cond.Right)
+	if err != nil {
+		return renderResult{}, err
+	}
+
+	switch cond.Operator {
+	case LogicalAnd:
+		return combineAnd(left, right), nil
+	case LogicalOr:
+		return combineOr(left, right), nil
+	default:
+		return renderResult{}, errors.Errorf("unsupported logical operator %s", cond.Operator)
+	}
+}
+
+func (r *renderer) renderNotCondition(cond *NotCondition) (renderResult, error) {
+	child, err := r.renderCondition(cond.Expr)
+	if err != nil {
+		return renderResult{}, err
+	}
+
+	if child.trivial {
+		return renderResult{sql: "1 = 0", unsatisfiable: true}, nil
+	}
+	if child.unsatisfiable {
+		return renderResult{trivial: true}, nil
+	}
+	return renderResult{
+		sql: fmt.Sprintf("NOT (%s)", child.sql),
+	}, nil
+}
+
+func (r *renderer) renderFieldPredicate(cond *FieldPredicateCondition) (renderResult, error) {
+	field, ok := r.schema.Field(cond.Field)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", cond.Field)
+	}
+
+	switch field.Kind {
+	case FieldKindBoolColumn:
+		column := qualifyColumn(r.dialect, field.Column)
+		return renderResult{
+			sql: fmt.Sprintf("%s IS TRUE", column),
+		}, nil
+	case FieldKindJSONBool:
+		sql, err := r.jsonBoolPredicate(field)
+		if err != nil {
+			return renderResult{}, err
+		}
+		return renderResult{sql: sql}, nil
+	default:
+		return renderResult{}, errors.Errorf("field %q cannot be used as a predicate", cond.Field)
+	}
+}
+
+func (r *renderer) renderComparison(cond *ComparisonCondition) (renderResult, error) {
+	switch left := cond.Left.(type) {
+	case *FieldRef:
+		field, ok := r.schema.Field(left.Name)
+		if !ok {
+			return renderResult{}, errors.Errorf("unknown field %q", left.Name)
+		}
+		switch field.Kind {
+		case FieldKindBoolColumn:
+			return r.renderBoolColumnComparison(field, cond.Operator, cond.Right)
+		case FieldKindJSONBool:
+			return r.renderJSONBoolComparison(field, cond.Operator, cond.Right)
+		case FieldKindScalar:
+			return r.renderScalarComparison(field, cond.Operator, cond.Right)
+		default:
+			return renderResult{}, errors.Errorf("field %q does not support comparison", field.Name)
+		}
+	case *FunctionValue:
+		return r.renderFunctionComparison(left, cond.Operator, cond.Right)
+	default:
+		return renderResult{}, errors.New("comparison must start with a field reference or supported function")
+	}
+}
+
+func (r *renderer) renderFunctionComparison(fn *FunctionValue, op ComparisonOperator, right ValueExpr) (renderResult, error) {
+	if fn.Name != "size" {
+		return renderResult{}, errors.Errorf("unsupported function %s in comparison", fn.Name)
+	}
+	if len(fn.Args) != 1 {
+		return renderResult{}, errors.New("size() expects one argument")
+	}
+	fieldArg, ok := fn.Args[0].(*FieldRef)
+	if !ok {
+		return renderResult{}, errors.New("size() argument must be a field")
+	}
+
+	field, ok := r.schema.Field(fieldArg.Name)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", fieldArg.Name)
+	}
+	if field.Kind != FieldKindJSONList {
+		return renderResult{}, errors.Errorf("size() only supports tag lists, got %q", field.Name)
+	}
+
+	value, err := expectNumericLiteral(right)
+	if err != nil {
+		return renderResult{}, err
+	}
+
+	expr := jsonArrayLengthExpr(r.dialect, field)
+	placeholder := r.addArg(value)
+	return renderResult{
+		sql: fmt.Sprintf("%s %s %s", expr, sqlOperator(op), placeholder),
+	}, nil
+}
+
+func (r *renderer) renderScalarComparison(field Field, op ComparisonOperator, right ValueExpr) (renderResult, error) {
+	lit, err := expectLiteral(right)
+	if err != nil {
+		return renderResult{}, err
+	}
+
+	columnExpr := field.columnExpr(r.dialect)
+	if lit == nil {
+		switch op {
+		case CompareEq:
+			return renderResult{sql: fmt.Sprintf("%s IS NULL", columnExpr)}, nil
+		case CompareNeq:
+			return renderResult{sql: fmt.Sprintf("%s IS NOT NULL", columnExpr)}, nil
+		default:
+			return renderResult{}, errors.Errorf("operator %s not supported for null comparison", op)
+		}
+	}
+
+	placeholder := ""
+	switch field.Type {
+	case FieldTypeString:
+		value, ok := lit.(string)
+		if !ok {
+			return renderResult{}, errors.Errorf("field %q expects string value", field.Name)
+		}
+		placeholder = r.addArg(value)
+	case FieldTypeInt, FieldTypeTimestamp:
+		num, err := toInt64(lit)
+		if err != nil {
+			return renderResult{}, errors.Wrapf(err, "field %q expects integer value", field.Name)
+		}
+		placeholder = r.addArg(num)
+	default:
+		return renderResult{}, errors.Errorf("unsupported data type %q for field %s", field.Type, field.Name)
+	}
+
+	return renderResult{
+		sql: fmt.Sprintf("%s %s %s", columnExpr, sqlOperator(op), placeholder),
+	}, nil
+}
+
+func (r *renderer) renderBoolColumnComparison(field Field, op ComparisonOperator, right ValueExpr) (renderResult, error) {
+	value, err := expectBool(right)
+	if err != nil {
+		return renderResult{}, err
+	}
+	placeholder := r.addBoolArg(value)
+	column := qualifyColumn(r.dialect, field.Column)
+	return renderResult{
+		sql: fmt.Sprintf("%s %s %s", column, sqlOperator(op), placeholder),
+	}, nil
+}
+
+func (r *renderer) renderJSONBoolComparison(field Field, op ComparisonOperator, right ValueExpr) (renderResult, error) {
+	value, err := expectBool(right)
+	if err != nil {
+		return renderResult{}, err
+	}
+
+	jsonExpr := jsonExtractExpr(r.dialect, field)
+	switch r.dialect {
+	case DialectSQLite:
+		switch op {
+		case CompareEq:
+			if field.Name == "has_task_list" {
+				target := "0"
+				if value {
+					target = "1"
+				}
+				return renderResult{sql: fmt.Sprintf("%s = %s", jsonExpr, target)}, nil
+			}
+			if value {
+				return renderResult{sql: fmt.Sprintf("%s IS TRUE", jsonExpr)}, nil
+			}
+			return renderResult{sql: fmt.Sprintf("NOT(%s IS TRUE)", jsonExpr)}, nil
+		case CompareNeq:
+			if field.Name == "has_task_list" {
+				target := "0"
+				if value {
+					target = "1"
+				}
+				return renderResult{sql: fmt.Sprintf("%s != %s", jsonExpr, target)}, nil
+			}
+			if value {
+				return renderResult{sql: fmt.Sprintf("NOT(%s IS TRUE)", jsonExpr)}, nil
+			}
+			return renderResult{sql: fmt.Sprintf("%s IS TRUE", jsonExpr)}, nil
+		default:
+			return renderResult{}, errors.Errorf("operator %s not supported for boolean JSON field", op)
+		}
+	case DialectMySQL:
+		boolStr := "false"
+		if value {
+			boolStr = "true"
+		}
+		return renderResult{
+			sql: fmt.Sprintf("%s %s CAST('%s' AS JSON)", jsonExpr, sqlOperator(op), boolStr),
+		}, nil
+	case DialectPostgres:
+		placeholder := r.addArg(value)
+		return renderResult{
+			sql: fmt.Sprintf("(%s)::boolean %s %s", jsonExpr, sqlOperator(op), placeholder),
+		}, nil
+	default:
+		return renderResult{}, errors.Errorf("unsupported dialect %s", r.dialect)
+	}
+}
+
+func (r *renderer) renderInCondition(cond *InCondition) (renderResult, error) {
+	fieldRef, ok := cond.Left.(*FieldRef)
+	if !ok {
+		return renderResult{}, errors.New("IN operator requires a field on the left-hand side")
+	}
+
+	if fieldRef.Name == "tag" {
+		return r.renderTagInList(cond.Values)
+	}
+
+	field, ok := r.schema.Field(fieldRef.Name)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", fieldRef.Name)
+	}
+
+	if field.Kind != FieldKindScalar {
+		return renderResult{}, errors.Errorf("field %q does not support IN()", fieldRef.Name)
+	}
+
+	return r.renderScalarInCondition(field, cond.Values)
+}
+
+func (r *renderer) renderTagInList(values []ValueExpr) (renderResult, error) {
+	field, ok := r.schema.ResolveAlias("tag")
+	if !ok {
+		return renderResult{}, errors.New("tag attribute is not configured")
+	}
+
+	conditions := make([]string, 0, len(values))
+	for _, v := range values {
+		lit, err := expectLiteral(v)
+		if err != nil {
+			return renderResult{}, err
+		}
+		str, ok := lit.(string)
+		if !ok {
+			return renderResult{}, errors.New("tags must be compared with string literals")
+		}
+
+		switch r.dialect {
+		case DialectSQLite:
+			// Support hierarchical tags: match exact tag OR tags with this prefix (e.g., "book" matches "book" and "book/something")
+			exactMatch := fmt.Sprintf("%s LIKE %s", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`%%"%s"%%`, str)))
+			prefixMatch := fmt.Sprintf("%s LIKE %s", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`%%"%s/%%`, str)))
+			expr := fmt.Sprintf("(%s OR %s)", exactMatch, prefixMatch)
+			conditions = append(conditions, expr)
+		case DialectMySQL:
+			// Support hierarchical tags: match exact tag OR tags with this prefix
+			exactMatch := fmt.Sprintf("JSON_CONTAINS(%s, %s)", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`"%s"`, str)))
+			prefixMatch := fmt.Sprintf("%s LIKE %s", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`%%"%s/%%`, str)))
+			expr := fmt.Sprintf("(%s OR %s)", exactMatch, prefixMatch)
+			conditions = append(conditions, expr)
+		case DialectPostgres:
+			// Support hierarchical tags: match exact tag OR tags with this prefix
+			exactMatch := fmt.Sprintf("%s @> jsonb_build_array(%s::json)", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`"%s"`, str)))
+			prefixMatch := fmt.Sprintf("(%s)::text LIKE %s", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`%%"%s/%%`, str)))
+			expr := fmt.Sprintf("(%s OR %s)", exactMatch, prefixMatch)
+			conditions = append(conditions, expr)
+		default:
+			return renderResult{}, errors.Errorf("unsupported dialect %s", r.dialect)
+		}
+	}
+
+	if len(conditions) == 1 {
+		return renderResult{sql: conditions[0]}, nil
+	}
+	return renderResult{
+		sql: fmt.Sprintf("(%s)", strings.Join(conditions, " OR ")),
+	}, nil
+}
+
+func (r *renderer) renderElementInCondition(cond *ElementInCondition) (renderResult, error) {
+	field, ok := r.schema.Field(cond.Field)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", cond.Field)
+	}
+	if field.Kind != FieldKindJSONList {
+		return renderResult{}, errors.Errorf("field %q is not a tag list", cond.Field)
+	}
+
+	lit, err := expectLiteral(cond.Element)
+	if err != nil {
+		return renderResult{}, err
+	}
+	str, ok := lit.(string)
+	if !ok {
+		return renderResult{}, errors.New("tags membership requires string literal")
+	}
+
+	switch r.dialect {
+	case DialectSQLite:
+		sql := fmt.Sprintf("%s LIKE %s", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`%%"%s"%%`, str)))
+		return renderResult{sql: sql}, nil
+	case DialectMySQL:
+		sql := fmt.Sprintf("JSON_CONTAINS(%s, %s)", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`"%s"`, str)))
+		return renderResult{sql: sql}, nil
+	case DialectPostgres:
+		sql := fmt.Sprintf("%s @> jsonb_build_array(%s::json)", jsonArrayExpr(r.dialect, field), r.addArg(fmt.Sprintf(`"%s"`, str)))
+		return renderResult{sql: sql}, nil
+	default:
+		return renderResult{}, errors.Errorf("unsupported dialect %s", r.dialect)
+	}
+}
+
+func (r *renderer) renderScalarInCondition(field Field, values []ValueExpr) (renderResult, error) {
+	placeholders := make([]string, 0, len(values))
+
+	for _, v := range values {
+		lit, err := expectLiteral(v)
+		if err != nil {
+			return renderResult{}, err
+		}
+		switch field.Type {
+		case FieldTypeString:
+			str, ok := lit.(string)
+			if !ok {
+				return renderResult{}, errors.Errorf("field %q expects string values", field.Name)
+			}
+			placeholders = append(placeholders, r.addArg(str))
+		case FieldTypeInt:
+			num, err := toInt64(lit)
+			if err != nil {
+				return renderResult{}, err
+			}
+			placeholders = append(placeholders, r.addArg(num))
+		default:
+			return renderResult{}, errors.Errorf("field %q does not support IN() comparisons", field.Name)
+		}
+	}
+
+	column := field.columnExpr(r.dialect)
+	return renderResult{
+		sql: fmt.Sprintf("%s IN (%s)", column, strings.Join(placeholders, ",")),
+	}, nil
+}
+
+func (r *renderer) renderContainsCondition(cond *ContainsCondition) (renderResult, error) {
+	field, ok := r.schema.Field(cond.Field)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", cond.Field)
+	}
+	column := field.columnExpr(r.dialect)
+	arg := fmt.Sprintf("%%%s%%", cond.Value)
+	switch r.dialect {
+	case DialectSQLite:
+		// Use custom Unicode-aware case folding function for case-insensitive comparison.
+		// This overcomes SQLite's ASCII-only LOWER() limitation.
+		sql := fmt.Sprintf("memos_unicode_lower(%s) LIKE memos_unicode_lower(%s)", column, r.addArg(arg))
+		return renderResult{sql: sql}, nil
+	case DialectPostgres:
+		sql := fmt.Sprintf("%s ILIKE %s", column, r.addArg(arg))
+		return renderResult{sql: sql}, nil
+	default:
+		sql := fmt.Sprintf("%s LIKE %s", column, r.addArg(arg))
+		return renderResult{sql: sql}, nil
+	}
+}
+
+func (r *renderer) renderListComprehension(cond *ListComprehensionCondition) (renderResult, error) {
+	field, ok := r.schema.Field(cond.Field)
+	if !ok {
+		return renderResult{}, errors.Errorf("unknown field %q", cond.Field)
+	}
+
+	if field.Kind != FieldKindJSONList {
+		return renderResult{}, errors.Errorf("field %q is not a JSON list", cond.Field)
+	}
+
+	// Render based on predicate type
+	switch pred := cond.Predicate.(type) {
+	case *StartsWithPredicate:
+		return r.renderTagStartsWith(field, pred.Prefix, cond.Kind)
+	case *EndsWithPredicate:
+		return r.renderTagEndsWith(field, pred.Suffix, cond.Kind)
+	case *ContainsPredicate:
+		return r.renderTagContains(field, pred.Substring, cond.Kind)
+	default:
+		return renderResult{}, errors.Errorf("unsupported predicate type %T in comprehension", pred)
+	}
+}
+
+// renderTagStartsWith generates SQL for tags.exists(t, t.startsWith("prefix")).
+func (r *renderer) renderTagStartsWith(field Field, prefix string, _ ComprehensionKind) (renderResult, error) {
+	arrayExpr := jsonArrayExpr(r.dialect, field)
+
+	switch r.dialect {
+	case DialectSQLite, DialectMySQL:
+		// Match exact tag or tags with this prefix (hierarchical support)
+		exactMatch := r.buildJSONArrayLike(arrayExpr, fmt.Sprintf(`%%"%s"%%`, prefix))
+		prefixMatch := r.buildJSONArrayLike(arrayExpr, fmt.Sprintf(`%%"%s%%`, prefix))
+		condition := fmt.Sprintf("(%s OR %s)", exactMatch, prefixMatch)
+		return renderResult{sql: r.wrapWithNullCheck(arrayExpr, condition)}, nil
+
+	case DialectPostgres:
+		// Use PostgreSQL's powerful JSON operators
+		exactMatch := fmt.Sprintf("%s @> jsonb_build_array(%s::json)", arrayExpr, r.addArg(fmt.Sprintf(`"%s"`, prefix)))
+		prefixMatch := fmt.Sprintf("(%s)::text LIKE %s", arrayExpr, r.addArg(fmt.Sprintf(`%%"%s%%`, prefix)))
+		condition := fmt.Sprintf("(%s OR %s)", exactMatch, prefixMatch)
+		return renderResult{sql: r.wrapWithNullCheck(arrayExpr, condition)}, nil
+
+	default:
+		return renderResult{}, errors.Errorf("unsupported dialect %s", r.dialect)
+	}
+}
+
+// renderTagEndsWith generates SQL for tags.exists(t, t.endsWith("suffix")).
+func (r *renderer) renderTagEndsWith(field Field, suffix string, _ ComprehensionKind) (renderResult, error) {
+	arrayExpr := jsonArrayExpr(r.dialect, field)
+	pattern := fmt.Sprintf(`%%%s"%%`, suffix)
+
+	likeExpr := r.buildJSONArrayLike(arrayExpr, pattern)
+	return renderResult{sql: r.wrapWithNullCheck(arrayExpr, likeExpr)}, nil
+}
+
+// renderTagContains generates SQL for tags.exists(t, t.contains("substring")).
+func (r *renderer) renderTagContains(field Field, substring string, _ ComprehensionKind) (renderResult, error) {
+	arrayExpr := jsonArrayExpr(r.dialect, field)
+	pattern := fmt.Sprintf(`%%%s%%`, substring)
+
+	likeExpr := r.buildJSONArrayLike(arrayExpr, pattern)
+	return renderResult{sql: r.wrapWithNullCheck(arrayExpr, likeExpr)}, nil
+}
+
+// buildJSONArrayLike builds a LIKE expression for matching within a JSON array.
+// Returns the LIKE clause without NULL/empty checks.
+func (r *renderer) buildJSONArrayLike(arrayExpr, pattern string) string {
+	switch r.dialect {
+	case DialectSQLite, DialectMySQL:
+		return fmt.Sprintf("%s LIKE %s", arrayExpr, r.addArg(pattern))
+	case DialectPostgres:
+		return fmt.Sprintf("(%s)::text LIKE %s", arrayExpr, r.addArg(pattern))
+	default:
+		return ""
+	}
+}
+
+// wrapWithNullCheck wraps a condition with NULL and empty array checks.
+// This ensures we don't match against NULL or empty JSON arrays.
+func (r *renderer) wrapWithNullCheck(arrayExpr, condition string) string {
+	var nullCheck string
+	switch r.dialect {
+	case DialectSQLite:
+		nullCheck = fmt.Sprintf("%s IS NOT NULL AND %s != '[]'", arrayExpr, arrayExpr)
+	case DialectMySQL:
+		nullCheck = fmt.Sprintf("%s IS NOT NULL AND JSON_LENGTH(%s) > 0", arrayExpr, arrayExpr)
+	case DialectPostgres:
+		nullCheck = fmt.Sprintf("%s IS NOT NULL AND jsonb_array_length(%s) > 0", arrayExpr, arrayExpr)
+	default:
+		return condition
+	}
+	return fmt.Sprintf("(%s AND %s)", condition, nullCheck)
+}
+
+func (r *renderer) jsonBoolPredicate(field Field) (string, error) {
+	expr := jsonExtractExpr(r.dialect, field)
+	switch r.dialect {
+	case DialectSQLite:
+		return fmt.Sprintf("%s IS TRUE", expr), nil
+	case DialectMySQL:
+		return fmt.Sprintf("COALESCE(%s, CAST('false' AS JSON)) = CAST('true' AS JSON)", expr), nil
+	case DialectPostgres:
+		return fmt.Sprintf("(%s)::boolean IS TRUE", expr), nil
+	default:
+		return "", errors.Errorf("unsupported dialect %s", r.dialect)
+	}
+}
+
+func combineAnd(left, right renderResult) renderResult {
+	if left.unsatisfiable || right.unsatisfiable {
+		return renderResult{sql: "1 = 0", unsatisfiable: true}
+	}
+	if left.trivial {
+		return right
+	}
+	if right.trivial {
+		return left
+	}
+	return renderResult{
+		sql: fmt.Sprintf("(%s AND %s)", left.sql, right.sql),
+	}
+}
+
+func combineOr(left, right renderResult) renderResult {
+	if left.trivial || right.trivial {
+		return renderResult{trivial: true}
+	}
+	if left.unsatisfiable {
+		return right
+	}
+	if right.unsatisfiable {
+		return left
+	}
+	return renderResult{
+		sql: fmt.Sprintf("(%s OR %s)", left.sql, right.sql),
+	}
+}
+
+func (r *renderer) addArg(value any) string {
+	r.placeholderCounter++
+	r.args = append(r.args, value)
+	if r.dialect == DialectPostgres {
+		return fmt.Sprintf("$%d", r.placeholderOffset+r.placeholderCounter)
+	}
+	return "?"
+}
+
+func (r *renderer) addBoolArg(value bool) string {
+	var v any
+	switch r.dialect {
+	case DialectSQLite:
+		if value {
+			v = 1
+		} else {
+			v = 0
+		}
+	default:
+		v = value
+	}
+	return r.addArg(v)
+}
+
+func expectLiteral(expr ValueExpr) (any, error) {
+	lit, ok := expr.(*LiteralValue)
+	if !ok {
+		return nil, errors.New("expression must be a literal")
+	}
+	return lit.Value, nil
+}
+
+func expectBool(expr ValueExpr) (bool, error) {
+	lit, err := expectLiteral(expr)
+	if err != nil {
+		return false, err
+	}
+	value, ok := lit.(bool)
+	if !ok {
+		return false, errors.New("boolean literal required")
+	}
+	return value, nil
+}
+
+func expectNumericLiteral(expr ValueExpr) (int64, error) {
+	lit, err := expectLiteral(expr)
+	if err != nil {
+		return 0, err
+	}
+	return toInt64(lit)
+}
+
+func toInt64(value any) (int64, error) {
+	switch v := value.(type) {
+	case int:
+		return int64(v), nil
+	case int32:
+		return int64(v), nil
+	case int64:
+		return v, nil
+	case uint32:
+		return int64(v), nil
+	case uint64:
+		return int64(v), nil
+	case float32:
+		return int64(v), nil
+	case float64:
+		return int64(v), nil
+	default:
+		return 0, errors.Errorf("cannot convert %T to int64", value)
+	}
+}
+
+func sqlOperator(op ComparisonOperator) string {
+	return string(op)
+}
+
+func qualifyColumn(d DialectName, col Column) string {
+	switch d {
+	case DialectPostgres:
+		return fmt.Sprintf("%s.%s", col.Table, col.Name)
+	default:
+		return fmt.Sprintf("`%s`.`%s`", col.Table, col.Name)
+	}
+}
+
+func jsonPath(field Field) string {
+	return "$." + strings.Join(field.JSONPath, ".")
+}
+
+func jsonExtractExpr(d DialectName, field Field) string {
+	column := qualifyColumn(d, field.Column)
+	switch d {
+	case DialectSQLite, DialectMySQL:
+		return fmt.Sprintf("JSON_EXTRACT(%s, '%s')", column, jsonPath(field))
+	case DialectPostgres:
+		return buildPostgresJSONAccessor(column, field.JSONPath, true)
+	default:
+		return ""
+	}
+}
+
+func jsonArrayExpr(d DialectName, field Field) string {
+	column := qualifyColumn(d, field.Column)
+	switch d {
+	case DialectSQLite, DialectMySQL:
+		return fmt.Sprintf("JSON_EXTRACT(%s, '%s')", column, jsonPath(field))
+	case DialectPostgres:
+		return buildPostgresJSONAccessor(column, field.JSONPath, false)
+	default:
+		return ""
+	}
+}
+
+func jsonArrayLengthExpr(d DialectName, field Field) string {
+	arrayExpr := jsonArrayExpr(d, field)
+	switch d {
+	case DialectSQLite:
+		return fmt.Sprintf("JSON_ARRAY_LENGTH(COALESCE(%s, JSON_ARRAY()))", arrayExpr)
+	case DialectMySQL:
+		return fmt.Sprintf("JSON_LENGTH(COALESCE(%s, JSON_ARRAY()))", arrayExpr)
+	case DialectPostgres:
+		return fmt.Sprintf("jsonb_array_length(COALESCE(%s, '[]'::jsonb))", arrayExpr)
+	default:
+		return ""
+	}
+}
+
+func buildPostgresJSONAccessor(base string, path []string, terminalText bool) string {
+	expr := base
+	for idx, part := range path {
+		if idx == len(path)-1 && terminalText {
+			expr = fmt.Sprintf("%s->>'%s'", expr, part)
+		} else {
+			expr = fmt.Sprintf("%s->'%s'", expr, part)
+		}
+	}
+	return expr
+}

plugin/filter/schema.go

@@ -0,0 +1,319 @@
+package filter
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/common/types"
+	"github.com/google/cel-go/common/types/ref"
+)
+
+// DialectName enumerates supported SQL dialects.
+type DialectName string
+
+const (
+	DialectSQLite   DialectName = "sqlite"
+	DialectMySQL    DialectName = "mysql"
+	DialectPostgres DialectName = "postgres"
+)
+
+// FieldType represents the logical type of a field.
+type FieldType string
+
+const (
+	FieldTypeString    FieldType = "string"
+	FieldTypeInt       FieldType = "int"
+	FieldTypeBool      FieldType = "bool"
+	FieldTypeTimestamp FieldType = "timestamp"
+)
+
+// FieldKind describes how a field is stored.
+type FieldKind string
+
+const (
+	FieldKindScalar       FieldKind = "scalar"
+	FieldKindBoolColumn   FieldKind = "bool_column"
+	FieldKindJSONBool     FieldKind = "json_bool"
+	FieldKindJSONList     FieldKind = "json_list"
+	FieldKindVirtualAlias FieldKind = "virtual_alias"
+)
+
+// Column identifies the backing table column.
+type Column struct {
+	Table string
+	Name  string
+}
+
+// Field captures the schema metadata for an exposed CEL identifier.
+type Field struct {
+	Name                 string
+	Kind                 FieldKind
+	Type                 FieldType
+	Column               Column
+	JSONPath             []string
+	AliasFor             string
+	SupportsContains     bool
+	Expressions          map[DialectName]string
+	AllowedComparisonOps map[ComparisonOperator]bool
+}
+
+// Schema collects CEL environment options and field metadata.
+type Schema struct {
+	Name       string
+	Fields     map[string]Field
+	EnvOptions []cel.EnvOption
+}
+
+// Field returns the field metadata if present.
+func (s Schema) Field(name string) (Field, bool) {
+	f, ok := s.Fields[name]
+	return f, ok
+}
+
+// ResolveAlias resolves a virtual alias to its target field.
+func (s Schema) ResolveAlias(name string) (Field, bool) {
+	field, ok := s.Fields[name]
+	if !ok {
+		return Field{}, false
+	}
+	if field.Kind == FieldKindVirtualAlias {
+		target, ok := s.Fields[field.AliasFor]
+		if !ok {
+			return Field{}, false
+		}
+		return target, true
+	}
+	return field, true
+}
+
+var nowFunction = cel.Function("now",
+	cel.Overload("now",
+		[]*cel.Type{},
+		cel.IntType,
+		cel.FunctionBinding(func(_ ...ref.Val) ref.Val {
+			return types.Int(time.Now().Unix())
+		}),
+	),
+)
+
+// NewSchema constructs the memo filter schema and CEL environment.
+func NewSchema() Schema {
+	fields := map[string]Field{
+		"content": {
+			Name:             "content",
+			Kind:             FieldKindScalar,
+			Type:             FieldTypeString,
+			Column:           Column{Table: "memo", Name: "content"},
+			SupportsContains: true,
+			Expressions:      map[DialectName]string{},
+		},
+		"creator_id": {
+			Name:        "creator_id",
+			Kind:        FieldKindScalar,
+			Type:        FieldTypeInt,
+			Column:      Column{Table: "memo", Name: "creator_id"},
+			Expressions: map[DialectName]string{},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"created_ts": {
+			Name:   "created_ts",
+			Kind:   FieldKindScalar,
+			Type:   FieldTypeTimestamp,
+			Column: Column{Table: "memo", Name: "created_ts"},
+			Expressions: map[DialectName]string{
+				// MySQL stores created_ts as TIMESTAMP, needs conversion to epoch
+				DialectMySQL: "UNIX_TIMESTAMP(%s)",
+				// PostgreSQL and SQLite store created_ts as BIGINT (epoch), no conversion needed
+				DialectPostgres: "%s",
+				DialectSQLite:   "%s",
+			},
+		},
+		"updated_ts": {
+			Name:   "updated_ts",
+			Kind:   FieldKindScalar,
+			Type:   FieldTypeTimestamp,
+			Column: Column{Table: "memo", Name: "updated_ts"},
+			Expressions: map[DialectName]string{
+				// MySQL stores updated_ts as TIMESTAMP, needs conversion to epoch
+				DialectMySQL: "UNIX_TIMESTAMP(%s)",
+				// PostgreSQL and SQLite store updated_ts as BIGINT (epoch), no conversion needed
+				DialectPostgres: "%s",
+				DialectSQLite:   "%s",
+			},
+		},
+		"pinned": {
+			Name:        "pinned",
+			Kind:        FieldKindBoolColumn,
+			Type:        FieldTypeBool,
+			Column:      Column{Table: "memo", Name: "pinned"},
+			Expressions: map[DialectName]string{},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"visibility": {
+			Name:        "visibility",
+			Kind:        FieldKindScalar,
+			Type:        FieldTypeString,
+			Column:      Column{Table: "memo", Name: "visibility"},
+			Expressions: map[DialectName]string{},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"tags": {
+			Name:     "tags",
+			Kind:     FieldKindJSONList,
+			Type:     FieldTypeString,
+			Column:   Column{Table: "memo", Name: "payload"},
+			JSONPath: []string{"tags"},
+		},
+		"tag": {
+			Name:     "tag",
+			Kind:     FieldKindVirtualAlias,
+			Type:     FieldTypeString,
+			AliasFor: "tags",
+		},
+		"has_task_list": {
+			Name:     "has_task_list",
+			Kind:     FieldKindJSONBool,
+			Type:     FieldTypeBool,
+			Column:   Column{Table: "memo", Name: "payload"},
+			JSONPath: []string{"property", "hasTaskList"},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"has_link": {
+			Name:     "has_link",
+			Kind:     FieldKindJSONBool,
+			Type:     FieldTypeBool,
+			Column:   Column{Table: "memo", Name: "payload"},
+			JSONPath: []string{"property", "hasLink"},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"has_code": {
+			Name:     "has_code",
+			Kind:     FieldKindJSONBool,
+			Type:     FieldTypeBool,
+			Column:   Column{Table: "memo", Name: "payload"},
+			JSONPath: []string{"property", "hasCode"},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+		"has_incomplete_tasks": {
+			Name:     "has_incomplete_tasks",
+			Kind:     FieldKindJSONBool,
+			Type:     FieldTypeBool,
+			Column:   Column{Table: "memo", Name: "payload"},
+			JSONPath: []string{"property", "hasIncompleteTasks"},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+	}
+
+	envOptions := []cel.EnvOption{
+		cel.Variable("content", cel.StringType),
+		cel.Variable("creator_id", cel.IntType),
+		cel.Variable("created_ts", cel.IntType),
+		cel.Variable("updated_ts", cel.IntType),
+		cel.Variable("pinned", cel.BoolType),
+		cel.Variable("tag", cel.StringType),
+		cel.Variable("tags", cel.ListType(cel.StringType)),
+		cel.Variable("visibility", cel.StringType),
+		cel.Variable("has_task_list", cel.BoolType),
+		cel.Variable("has_link", cel.BoolType),
+		cel.Variable("has_code", cel.BoolType),
+		cel.Variable("has_incomplete_tasks", cel.BoolType),
+		nowFunction,
+	}
+
+	return Schema{
+		Name:       "memo",
+		Fields:     fields,
+		EnvOptions: envOptions,
+	}
+}
+
+// NewAttachmentSchema constructs the attachment filter schema and CEL environment.
+func NewAttachmentSchema() Schema {
+	fields := map[string]Field{
+		"filename": {
+			Name:             "filename",
+			Kind:             FieldKindScalar,
+			Type:             FieldTypeString,
+			Column:           Column{Table: "attachment", Name: "filename"},
+			SupportsContains: true,
+			Expressions:      map[DialectName]string{},
+		},
+		"mime_type": {
+			Name:        "mime_type",
+			Kind:        FieldKindScalar,
+			Type:        FieldTypeString,
+			Column:      Column{Table: "attachment", Name: "type"},
+			Expressions: map[DialectName]string{},
+		},
+		"create_time": {
+			Name:   "create_time",
+			Kind:   FieldKindScalar,
+			Type:   FieldTypeTimestamp,
+			Column: Column{Table: "attachment", Name: "created_ts"},
+			Expressions: map[DialectName]string{
+				// MySQL stores created_ts as TIMESTAMP, needs conversion to epoch
+				DialectMySQL: "UNIX_TIMESTAMP(%s)",
+				// PostgreSQL and SQLite store created_ts as BIGINT (epoch), no conversion needed
+				DialectPostgres: "%s",
+				DialectSQLite:   "%s",
+			},
+		},
+		"memo_id": {
+			Name:        "memo_id",
+			Kind:        FieldKindScalar,
+			Type:        FieldTypeInt,
+			Column:      Column{Table: "attachment", Name: "memo_id"},
+			Expressions: map[DialectName]string{},
+			AllowedComparisonOps: map[ComparisonOperator]bool{
+				CompareEq:  true,
+				CompareNeq: true,
+			},
+		},
+	}
+
+	envOptions := []cel.EnvOption{
+		cel.Variable("filename", cel.StringType),
+		cel.Variable("mime_type", cel.StringType),
+		cel.Variable("create_time", cel.IntType),
+		cel.Variable("memo_id", cel.AnyType),
+		nowFunction,
+	}
+
+	return Schema{
+		Name:       "attachment",
+		Fields:     fields,
+		EnvOptions: envOptions,
+	}
+}
+
+// columnExpr returns the field expression for the given dialect, applying
+// any schema-specific overrides (e.g. UNIX timestamp conversions).
+func (f Field) columnExpr(d DialectName) string {
+	base := qualifyColumn(d, f.Column)
+	if expr, ok := f.Expressions[d]; ok && expr != "" {
+		return fmt.Sprintf(expr, base)
+	}
+	return base
+}

plugin/httpgetter/html_meta.go

@@ -0,0 +1,166 @@
+package httpgetter
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+
+	"github.com/pkg/errors"
+	"golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
+)
+
+var ErrInternalIP = errors.New("internal IP addresses are not allowed")
+
+var httpClient = &http.Client{
+	CheckRedirect: func(req *http.Request, via []*http.Request) error {
+		if err := validateURL(req.URL.String()); err != nil {
+			return errors.Wrap(err, "redirect to internal IP")
+		}
+		if len(via) >= 10 {
+			return errors.New("too many redirects")
+		}
+		return nil
+	},
+}
+
+type HTMLMeta struct {
+	Title       string `json:"title"`
+	Description string `json:"description"`
+	Image       string `json:"image"`
+}
+
+func GetHTMLMeta(urlStr string) (*HTMLMeta, error) {
+	if err := validateURL(urlStr); err != nil {
+		return nil, err
+	}
+
+	response, err := httpClient.Get(urlStr)
+	if err != nil {
+		return nil, err
+	}
+	defer response.Body.Close()
+
+	mediatype, err := getMediatype(response)
+	if err != nil {
+		return nil, err
+	}
+	if mediatype != "text/html" {
+		return nil, errors.New("not a HTML page")
+	}
+
+	// TODO: limit the size of the response body
+
+	htmlMeta := extractHTMLMeta(response.Body)
+	enrichSiteMeta(response.Request.URL, htmlMeta)
+	return htmlMeta, nil
+}
+
+func extractHTMLMeta(resp io.Reader) *HTMLMeta {
+	tokenizer := html.NewTokenizer(resp)
+	htmlMeta := new(HTMLMeta)
+
+	for {
+		tokenType := tokenizer.Next()
+		if tokenType == html.ErrorToken {
+			break
+		} else if tokenType == html.StartTagToken || tokenType == html.SelfClosingTagToken {
+			token := tokenizer.Token()
+			if token.DataAtom == atom.Body {
+				break
+			}
+
+			if token.DataAtom == atom.Title {
+				tokenizer.Next()
+				token := tokenizer.Token()
+				htmlMeta.Title = token.Data
+			} else if token.DataAtom == atom.Meta {
+				description, ok := extractMetaProperty(token, "description")
+				if ok {
+					htmlMeta.Description = description
+				}
+
+				ogTitle, ok := extractMetaProperty(token, "og:title")
+				if ok {
+					htmlMeta.Title = ogTitle
+				}
+
+				ogDescription, ok := extractMetaProperty(token, "og:description")
+				if ok {
+					htmlMeta.Description = ogDescription
+				}
+
+				ogImage, ok := extractMetaProperty(token, "og:image")
+				if ok {
+					htmlMeta.Image = ogImage
+				}
+			}
+		}
+	}
+
+	return htmlMeta
+}
+
+func extractMetaProperty(token html.Token, prop string) (content string, ok bool) {
+	content, ok = "", false
+	for _, attr := range token.Attr {
+		if attr.Key == "property" && attr.Val == prop {
+			ok = true
+		}
+		if attr.Key == "content" {
+			content = attr.Val
+		}
+	}
+	return content, ok
+}
+
+func validateURL(urlStr string) error {
+	u, err := url.Parse(urlStr)
+	if err != nil {
+		return errors.New("invalid URL format")
+	}
+
+	if u.Scheme != "http" && u.Scheme != "https" {
+		return errors.New("only http/https protocols are allowed")
+	}
+
+	host := u.Hostname()
+	if host == "" {
+		return errors.New("empty hostname")
+	}
+
+	// check if the hostname is an IP
+	if ip := net.ParseIP(host); ip != nil {
+		if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast() {
+			return errors.Wrap(ErrInternalIP, ip.String())
+		}
+		return nil
+	}
+
+	// check if it's a hostname, resolve it and check all returned IPs
+	ips, err := net.LookupIP(host)
+	if err != nil {
+		return errors.Errorf("failed to resolve hostname: %v", err)
+	}
+
+	for _, ip := range ips {
+		if ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast() {
+			return errors.Wrapf(ErrInternalIP, "host=%s, ip=%s", host, ip.String())
+		}
+	}
+
+	return nil
+}
+
+func enrichSiteMeta(url *url.URL, meta *HTMLMeta) {
+	if url.Hostname() == "www.youtube.com" {
+		if url.Path == "/watch" {
+			vid := url.Query().Get("v")
+			if vid != "" {
+				meta.Image = fmt.Sprintf("https://img.youtube.com/vi/%s/mqdefault.jpg", vid)
+			}
+		}
+	}
+}

plugin/httpgetter/html_meta_test.go

@@ -0,0 +1,32 @@
+package httpgetter
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetHTMLMeta(t *testing.T) {
+	tests := []struct {
+		urlStr   string
+		htmlMeta HTMLMeta
+	}{}
+	for _, test := range tests {
+		metadata, err := GetHTMLMeta(test.urlStr)
+		require.NoError(t, err)
+		require.Equal(t, test.htmlMeta, *metadata)
+	}
+}
+
+func TestGetHTMLMetaForInternal(t *testing.T) {
+	// test for internal IP
+	if _, err := GetHTMLMeta("http://192.168.0.1"); !errors.Is(err, ErrInternalIP) {
+		t.Errorf("Expected error for internal IP, got %v", err)
+	}
+
+	// test for resolved internal IP
+	if _, err := GetHTMLMeta("http://localhost"); !errors.Is(err, ErrInternalIP) {
+		t.Errorf("Expected error for resolved internal IP, got %v", err)
+	}
+}

plugin/httpgetter/http_getter.go

@@ -0,0 +1 @@
+package httpgetter

plugin/httpgetter/image.go

@@ -0,0 +1,45 @@
+package httpgetter
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+type Image struct {
+	Blob      []byte
+	Mediatype string
+}
+
+func GetImage(urlStr string) (*Image, error) {
+	if _, err := url.Parse(urlStr); err != nil {
+		return nil, err
+	}
+
+	response, err := http.Get(urlStr)
+	if err != nil {
+		return nil, err
+	}
+	defer response.Body.Close()
+
+	mediatype, err := getMediatype(response)
+	if err != nil {
+		return nil, err
+	}
+	if !strings.HasPrefix(mediatype, "image/") {
+		return nil, errors.New("wrong image mediatype")
+	}
+
+	bodyBytes, err := io.ReadAll(response.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	image := &Image{
+		Blob:      bodyBytes,
+		Mediatype: mediatype,
+	}
+	return image, nil
+}

plugin/httpgetter/util.go

@@ -0,0 +1,15 @@
+package httpgetter
+
+import (
+	"mime"
+	"net/http"
+)
+
+func getMediatype(response *http.Response) (string, error) {
+	contentType := response.Header.Get("content-type")
+	mediatype, _, err := mime.ParseMediaType(contentType)
+	if err != nil {
+		return "", err
+	}
+	return mediatype, nil
+}

plugin/idp/idp.go

@@ -0,0 +1,8 @@
+package idp
+
+type IdentityProviderUserInfo struct {
+	Identifier  string
+	DisplayName string
+	Email       string
+	AvatarURL   string
+}

plugin/idp/oauth2/oauth2.go

@@ -0,0 +1,134 @@
+// Package oauth2 is the plugin for OAuth2 Identity Provider.
+package oauth2
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+
+	"github.com/pkg/errors"
+	"golang.org/x/oauth2"
+
+	"github.com/usememos/memos/plugin/idp"
+	storepb "github.com/usememos/memos/proto/gen/store"
+)
+
+// IdentityProvider represents an OAuth2 Identity Provider.
+type IdentityProvider struct {
+	config *storepb.OAuth2Config
+}
+
+// NewIdentityProvider initializes a new OAuth2 Identity Provider with the given configuration.
+func NewIdentityProvider(config *storepb.OAuth2Config) (*IdentityProvider, error) {
+	for v, field := range map[string]string{
+		config.ClientId:                "clientId",
+		config.ClientSecret:            "clientSecret",
+		config.TokenUrl:                "tokenUrl",
+		config.UserInfoUrl:             "userInfoUrl",
+		config.FieldMapping.Identifier: "fieldMapping.identifier",
+	} {
+		if v == "" {
+			return nil, errors.Errorf(`the field "%s" is empty but required`, field)
+		}
+	}
+
+	return &IdentityProvider{
+		config: config,
+	}, nil
+}
+
+// ExchangeToken returns the exchanged OAuth2 token using the given authorization code.
+// If codeVerifier is provided, it will be used for PKCE (Proof Key for Code Exchange) validation.
+func (p *IdentityProvider) ExchangeToken(ctx context.Context, redirectURL, code, codeVerifier string) (string, error) {
+	conf := &oauth2.Config{
+		ClientID:     p.config.ClientId,
+		ClientSecret: p.config.ClientSecret,
+		RedirectURL:  redirectURL,
+		Scopes:       p.config.Scopes,
+		Endpoint: oauth2.Endpoint{
+			AuthURL:   p.config.AuthUrl,
+			TokenURL:  p.config.TokenUrl,
+			AuthStyle: oauth2.AuthStyleInParams,
+		},
+	}
+
+	// Prepare token exchange options
+	opts := []oauth2.AuthCodeOption{}
+
+	// Add PKCE code_verifier if provided
+	if codeVerifier != "" {
+		opts = append(opts, oauth2.SetAuthURLParam("code_verifier", codeVerifier))
+	}
+
+	token, err := conf.Exchange(ctx, code, opts...)
+	if err != nil {
+		return "", errors.Wrap(err, "failed to exchange access token")
+	}
+
+	// Use the standard AccessToken field instead of Extra()
+	// This is more reliable across different OAuth providers
+	if token.AccessToken == "" {
+		return "", errors.New("missing access token from authorization response")
+	}
+
+	return token.AccessToken, nil
+}
+
+// UserInfo returns the parsed user information using the given OAuth2 token.
+func (p *IdentityProvider) UserInfo(token string) (*idp.IdentityProviderUserInfo, error) {
+	client := &http.Client{}
+	req, err := http.NewRequest(http.MethodGet, p.config.UserInfoUrl, nil)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to new http request")
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", token))
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to get user information")
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read response body")
+	}
+
+	var claims map[string]any
+	if err := json.Unmarshal(body, &claims); err != nil {
+		return nil, errors.Wrap(err, "failed to unmarshal response body")
+	}
+	slog.Info("user info claims", "claims", claims)
+	userInfo := &idp.IdentityProviderUserInfo{}
+	if v, ok := claims[p.config.FieldMapping.Identifier].(string); ok {
+		userInfo.Identifier = v
+	}
+	if userInfo.Identifier == "" {
+		return nil, errors.Errorf("the field %q is not found in claims or has empty value", p.config.FieldMapping.Identifier)
+	}
+
+	// Best effort to map optional fields
+	if p.config.FieldMapping.DisplayName != "" {
+		if v, ok := claims[p.config.FieldMapping.DisplayName].(string); ok {
+			userInfo.DisplayName = v
+		}
+	}
+	if userInfo.DisplayName == "" {
+		userInfo.DisplayName = userInfo.Identifier
+	}
+	if p.config.FieldMapping.Email != "" {
+		if v, ok := claims[p.config.FieldMapping.Email].(string); ok {
+			userInfo.Email = v
+		}
+	}
+	if p.config.FieldMapping.AvatarUrl != "" {
+		if v, ok := claims[p.config.FieldMapping.AvatarUrl].(string); ok {
+			userInfo.AvatarURL = v
+		}
+	}
+	slog.Info("user info", "userInfo", userInfo)
+	return userInfo, nil
+}

plugin/idp/oauth2/oauth2_test.go

@@ -0,0 +1,164 @@
+package oauth2
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/usememos/memos/plugin/idp"
+	storepb "github.com/usememos/memos/proto/gen/store"
+)
+
+func TestNewIdentityProvider(t *testing.T) {
+	tests := []struct {
+		name        string
+		config      *storepb.OAuth2Config
+		containsErr string
+	}{
+		{
+			name: "no tokenUrl",
+			config: &storepb.OAuth2Config{
+				ClientId:     "test-client-id",
+				ClientSecret: "test-client-secret",
+				AuthUrl:      "",
+				TokenUrl:     "",
+				UserInfoUrl:  "https://example.com/api/user",
+				FieldMapping: &storepb.FieldMapping{
+					Identifier: "login",
+				},
+			},
+			containsErr: `the field "tokenUrl" is empty but required`,
+		},
+		{
+			name: "no userInfoUrl",
+			config: &storepb.OAuth2Config{
+				ClientId:     "test-client-id",
+				ClientSecret: "test-client-secret",
+				AuthUrl:      "",
+				TokenUrl:     "https://example.com/token",
+				UserInfoUrl:  "",
+				FieldMapping: &storepb.FieldMapping{
+					Identifier: "login",
+				},
+			},
+			containsErr: `the field "userInfoUrl" is empty but required`,
+		},
+		{
+			name: "no field mapping identifier",
+			config: &storepb.OAuth2Config{
+				ClientId:     "test-client-id",
+				ClientSecret: "test-client-secret",
+				AuthUrl:      "",
+				TokenUrl:     "https://example.com/token",
+				UserInfoUrl:  "https://example.com/api/user",
+				FieldMapping: &storepb.FieldMapping{
+					Identifier: "",
+				},
+			},
+			containsErr: `the field "fieldMapping.identifier" is empty but required`,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(*testing.T) {
+			_, err := NewIdentityProvider(test.config)
+			assert.ErrorContains(t, err, test.containsErr)
+		})
+	}
+}
+
+func newMockServer(t *testing.T, code, accessToken string, userinfo []byte) *httptest.Server {
+	mux := http.NewServeMux()
+
+	var rawIDToken string
+	mux.HandleFunc("/oauth2/token", func(w http.ResponseWriter, r *http.Request) {
+		require.Equal(t, http.MethodPost, r.Method)
+
+		body, err := io.ReadAll(r.Body)
+		require.NoError(t, err)
+		vals, err := url.ParseQuery(string(body))
+		require.NoError(t, err)
+
+		require.Equal(t, code, vals.Get("code"))
+		require.Equal(t, "authorization_code", vals.Get("grant_type"))
+
+		w.Header().Set("Content-Type", "application/json")
+		err = json.NewEncoder(w).Encode(map[string]any{
+			"access_token": accessToken,
+			"token_type":   "Bearer",
+			"expires_in":   3600,
+			"id_token":     rawIDToken,
+		})
+		require.NoError(t, err)
+	})
+	mux.HandleFunc("/oauth2/userinfo", func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, err := w.Write(userinfo)
+		require.NoError(t, err)
+	})
+
+	s := httptest.NewServer(mux)
+
+	return s
+}
+
+func TestIdentityProvider(t *testing.T) {
+	ctx := context.Background()
+
+	const (
+		testClientID    = "test-client-id"
+		testCode        = "test-code"
+		testAccessToken = "test-access-token"
+		testSubject     = "123456789"
+		testName        = "John Doe"
+		testEmail       = "john.doe@example.com"
+	)
+	userInfo, err := json.Marshal(
+		map[string]any{
+			"sub":   testSubject,
+			"name":  testName,
+			"email": testEmail,
+		},
+	)
+	require.NoError(t, err)
+
+	s := newMockServer(t, testCode, testAccessToken, userInfo)
+
+	oauth2, err := NewIdentityProvider(
+		&storepb.OAuth2Config{
+			ClientId:     testClientID,
+			ClientSecret: "test-client-secret",
+			TokenUrl:     fmt.Sprintf("%s/oauth2/token", s.URL),
+			UserInfoUrl:  fmt.Sprintf("%s/oauth2/userinfo", s.URL),
+			FieldMapping: &storepb.FieldMapping{
+				Identifier:  "sub",
+				DisplayName: "name",
+				Email:       "email",
+			},
+		},
+	)
+	require.NoError(t, err)
+
+	redirectURL := "https://example.com/oauth/callback"
+	// Test without PKCE (backward compatibility)
+	oauthToken, err := oauth2.ExchangeToken(ctx, redirectURL, testCode, "")
+	require.NoError(t, err)
+	require.Equal(t, testAccessToken, oauthToken)
+
+	userInfoResult, err := oauth2.UserInfo(oauthToken)
+	require.NoError(t, err)
+
+	wantUserInfo := &idp.IdentityProviderUserInfo{
+		Identifier:  testSubject,
+		DisplayName: testName,
+		Email:       testEmail,
+	}
+	assert.Equal(t, wantUserInfo, userInfoResult)
+}

plugin/markdown/ast/tag.go

@@ -0,0 +1,28 @@
+package ast
+
+import (
+	gast "github.com/yuin/goldmark/ast"
+)
+
+// TagNode represents a #tag in the markdown AST.
+type TagNode struct {
+	gast.BaseInline
+
+	// Tag name without the # prefix
+	Tag []byte
+}
+
+// KindTag is the NodeKind for TagNode.
+var KindTag = gast.NewNodeKind("Tag")
+
+// Kind returns KindTag.
+func (*TagNode) Kind() gast.NodeKind {
+	return KindTag
+}
+
+// Dump implements Node.Dump for debugging.
+func (n *TagNode) Dump(source []byte, level int) {
+	gast.DumpHelper(n, source, level, map[string]string{
+		"Tag": string(n.Tag),
+	}, nil)
+}

plugin/markdown/extensions/tag.go

@@ -0,0 +1,24 @@
+package extensions
+
+import (
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/util"
+
+	mparser "github.com/usememos/memos/plugin/markdown/parser"
+)
+
+type tagExtension struct{}
+
+// TagExtension is a goldmark extension for #tag syntax.
+var TagExtension = &tagExtension{}
+
+// Extend extends the goldmark parser with tag support.
+func (*tagExtension) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(
+		parser.WithInlineParsers(
+			// Priority 200 - run before standard link parser (500)
+			util.Prioritized(mparser.NewTagParser(), 200),
+		),
+	)
+}

plugin/markdown/markdown.go

@@ -0,0 +1,409 @@
+package markdown
+
+import (
+	"bytes"
+	"strings"
+
+	"github.com/yuin/goldmark"
+	gast "github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/extension"
+	east "github.com/yuin/goldmark/extension/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+
+	mast "github.com/usememos/memos/plugin/markdown/ast"
+	"github.com/usememos/memos/plugin/markdown/extensions"
+	"github.com/usememos/memos/plugin/markdown/renderer"
+	storepb "github.com/usememos/memos/proto/gen/store"
+)
+
+// ExtractedData contains all metadata extracted from markdown in a single pass.
+type ExtractedData struct {
+	Tags     []string
+	Property *storepb.MemoPayload_Property
+}
+
+// Service handles markdown metadata extraction.
+// It uses goldmark to parse markdown and extract tags, properties, and snippets.
+// HTML rendering is primarily done on frontend using markdown-it, but backend provides
+// RenderHTML for RSS feeds and other server-side rendering needs.
+type Service interface {
+	// ExtractAll extracts tags, properties, and references in a single parse (most efficient)
+	ExtractAll(content []byte) (*ExtractedData, error)
+
+	// ExtractTags returns all #tags found in content
+	ExtractTags(content []byte) ([]string, error)
+
+	// ExtractProperties computes boolean properties
+	ExtractProperties(content []byte) (*storepb.MemoPayload_Property, error)
+
+	// RenderMarkdown renders goldmark AST back to markdown text
+	RenderMarkdown(content []byte) (string, error)
+
+	// RenderHTML renders markdown content to HTML
+	RenderHTML(content []byte) (string, error)
+
+	// GenerateSnippet creates plain text summary
+	GenerateSnippet(content []byte, maxLength int) (string, error)
+
+	// ValidateContent checks for syntax errors
+	ValidateContent(content []byte) error
+
+	// RenameTag renames all occurrences of oldTag to newTag in content
+	RenameTag(content []byte, oldTag, newTag string) (string, error)
+}
+
+// service implements the Service interface.
+type service struct {
+	md goldmark.Markdown
+}
+
+// Option configures the markdown service.
+type Option func(*config)
+
+type config struct {
+	enableTags bool
+}
+
+// WithTagExtension enables #tag parsing.
+func WithTagExtension() Option {
+	return func(c *config) {
+		c.enableTags = true
+	}
+}
+
+// NewService creates a new markdown service with the given options.
+func NewService(opts ...Option) Service {
+	cfg := &config{}
+	for _, opt := range opts {
+		opt(cfg)
+	}
+
+	exts := []goldmark.Extender{
+		extension.GFM, // GitHub Flavored Markdown (tables, strikethrough, task lists, autolinks)
+	}
+
+	// Add custom extensions based on config
+	if cfg.enableTags {
+		exts = append(exts, extensions.TagExtension)
+	}
+
+	md := goldmark.New(
+		goldmark.WithExtensions(exts...),
+		goldmark.WithParserOptions(
+			parser.WithAutoHeadingID(), // Generate heading IDs
+		),
+	)
+
+	return &service{
+		md: md,
+	}
+}
+
+// parse is an internal helper to parse content into AST.
+func (s *service) parse(content []byte) (gast.Node, error) {
+	reader := text.NewReader(content)
+	doc := s.md.Parser().Parse(reader)
+	return doc, nil
+}
+
+// ExtractTags returns all #tags found in content.
+func (s *service) ExtractTags(content []byte) ([]string, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return nil, err
+	}
+
+	var tags []string
+
+	// Walk the AST to find tag nodes
+	err = gast.Walk(root, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		if !entering {
+			return gast.WalkContinue, nil
+		}
+
+		// Check for custom TagNode
+		if tagNode, ok := n.(*mast.TagNode); ok {
+			tags = append(tags, string(tagNode.Tag))
+		}
+
+		return gast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Deduplicate tags while preserving original case
+	return uniquePreserveCase(tags), nil
+}
+
+// ExtractProperties computes boolean properties about the content.
+func (s *service) ExtractProperties(content []byte) (*storepb.MemoPayload_Property, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return nil, err
+	}
+
+	prop := &storepb.MemoPayload_Property{}
+
+	err = gast.Walk(root, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		if !entering {
+			return gast.WalkContinue, nil
+		}
+
+		switch n.Kind() {
+		case gast.KindLink:
+			prop.HasLink = true
+
+		case gast.KindCodeBlock, gast.KindFencedCodeBlock, gast.KindCodeSpan:
+			prop.HasCode = true
+
+		case east.KindTaskCheckBox:
+			prop.HasTaskList = true
+			if checkBox, ok := n.(*east.TaskCheckBox); ok {
+				if !checkBox.IsChecked {
+					prop.HasIncompleteTasks = true
+				}
+			}
+		default:
+			// No special handling for other node types
+		}
+
+		return gast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return prop, nil
+}
+
+// RenderMarkdown renders goldmark AST back to markdown text.
+func (s *service) RenderMarkdown(content []byte) (string, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return "", err
+	}
+
+	mdRenderer := renderer.NewMarkdownRenderer()
+	return mdRenderer.Render(root, content), nil
+}
+
+// RenderHTML renders markdown content to HTML using goldmark's built-in HTML renderer.
+func (s *service) RenderHTML(content []byte) (string, error) {
+	var buf bytes.Buffer
+	if err := s.md.Convert(content, &buf); err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}
+
+// GenerateSnippet creates a plain text summary from markdown content.
+func (s *service) GenerateSnippet(content []byte, maxLength int) (string, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return "", err
+	}
+
+	var buf strings.Builder
+	var lastNodeWasBlock bool
+
+	err = gast.Walk(root, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		if entering {
+			// Skip code blocks and code spans entirely
+			switch n.Kind() {
+			case gast.KindCodeBlock, gast.KindFencedCodeBlock, gast.KindCodeSpan:
+				return gast.WalkSkipChildren, nil
+			default:
+				// Continue walking for other node types
+			}
+
+			// Add space before block elements (except first)
+			switch n.Kind() {
+			case gast.KindParagraph, gast.KindHeading, gast.KindListItem:
+				if buf.Len() > 0 && lastNodeWasBlock {
+					buf.WriteByte(' ')
+				}
+			default:
+				// No space needed for other node types
+			}
+		}
+
+		if !entering {
+			// Mark that we just exited a block element
+			switch n.Kind() {
+			case gast.KindParagraph, gast.KindHeading, gast.KindListItem:
+				lastNodeWasBlock = true
+			default:
+				// Not a block element
+			}
+			return gast.WalkContinue, nil
+		}
+
+		lastNodeWasBlock = false
+
+		// Only extract plain text nodes
+		if textNode, ok := n.(*gast.Text); ok {
+			segment := textNode.Segment
+			buf.Write(segment.Value(content))
+
+			// Add space if this is a soft line break
+			if textNode.SoftLineBreak() {
+				buf.WriteByte(' ')
+			}
+		}
+
+		// Stop walking if we've exceeded double the max length
+		// (we'll truncate precisely later)
+		if buf.Len() > maxLength*2 {
+			return gast.WalkStop, nil
+		}
+
+		return gast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return "", err
+	}
+
+	snippet := buf.String()
+
+	// Truncate at word boundary if needed
+	if len(snippet) > maxLength {
+		snippet = truncateAtWord(snippet, maxLength)
+	}
+
+	return strings.TrimSpace(snippet), nil
+}
+
+// ValidateContent checks if the markdown content is valid.
+func (s *service) ValidateContent(content []byte) error {
+	// Try to parse the content
+	_, err := s.parse(content)
+	return err
+}
+
+// ExtractAll extracts tags, properties, and references in a single parse for efficiency.
+func (s *service) ExtractAll(content []byte) (*ExtractedData, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return nil, err
+	}
+
+	data := &ExtractedData{
+		Tags:     []string{},
+		Property: &storepb.MemoPayload_Property{},
+	}
+
+	// Single walk to collect all data
+	err = gast.Walk(root, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		if !entering {
+			return gast.WalkContinue, nil
+		}
+
+		// Extract tags
+		if tagNode, ok := n.(*mast.TagNode); ok {
+			data.Tags = append(data.Tags, string(tagNode.Tag))
+		}
+
+		// Extract properties based on node kind
+		switch n.Kind() {
+		case gast.KindLink:
+			data.Property.HasLink = true
+
+		case gast.KindCodeBlock, gast.KindFencedCodeBlock, gast.KindCodeSpan:
+			data.Property.HasCode = true
+
+		case east.KindTaskCheckBox:
+			data.Property.HasTaskList = true
+			if checkBox, ok := n.(*east.TaskCheckBox); ok {
+				if !checkBox.IsChecked {
+					data.Property.HasIncompleteTasks = true
+				}
+			}
+		default:
+			// No special handling for other node types
+		}
+
+		return gast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Deduplicate tags while preserving original case
+	data.Tags = uniquePreserveCase(data.Tags)
+
+	return data, nil
+}
+
+// RenameTag renames all occurrences of oldTag to newTag in content.
+func (s *service) RenameTag(content []byte, oldTag, newTag string) (string, error) {
+	root, err := s.parse(content)
+	if err != nil {
+		return "", err
+	}
+
+	// Walk the AST to find and rename tag nodes
+	err = gast.Walk(root, func(n gast.Node, entering bool) (gast.WalkStatus, error) {
+		if !entering {
+			return gast.WalkContinue, nil
+		}
+
+		// Check for custom TagNode and rename if it matches
+		if tagNode, ok := n.(*mast.TagNode); ok {
+			if string(tagNode.Tag) == oldTag {
+				tagNode.Tag = []byte(newTag)
+			}
+		}
+
+		return gast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return "", err
+	}
+
+	// Render back to markdown using the already-parsed AST
+	mdRenderer := renderer.NewMarkdownRenderer()
+	return mdRenderer.Render(root, content), nil
+}
+
+// uniquePreserveCase returns unique strings from input while preserving case.
+func uniquePreserveCase(strs []string) []string {
+	seen := make(map[string]struct{})
+	var result []string
+
+	for _, s := range strs {
+		if _, exists := seen[s]; !exists {
+			seen[s] = struct{}{}
+			result = append(result, s)
+		}
+	}
+
+	return result
+}
+
+// truncateAtWord truncates a string at the last word boundary before maxLength.
+// maxLength is treated as a rune (character) count to properly handle UTF-8 multi-byte characters.
+func truncateAtWord(s string, maxLength int) string {
+	// Convert to runes to properly handle multi-byte UTF-8 characters
+	runes := []rune(s)
+	if len(runes) <= maxLength {
+		return s
+	}
+
+	// Truncate to max length (by character count, not byte count)
+	truncated := string(runes[:maxLength])
+
+	// Find last space to avoid cutting in the middle of a word
+	lastSpace := strings.LastIndexAny(truncated, " \t\n\r")
+	if lastSpace > 0 {
+		truncated = truncated[:lastSpace]
+	}
+
+	return truncated + " ..."
+}

plugin/markdown/markdown_test.go

@@ -0,0 +1,448 @@
+package markdown
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewService(t *testing.T) {
+	svc := NewService()
+	assert.NotNil(t, svc)
+}
+
+func TestValidateContent(t *testing.T) {
+	svc := NewService()
+
+	tests := []struct {
+		name    string
+		content string
+		wantErr bool
+	}{
+		{
+			name:    "valid markdown",
+			content: "# Hello\n\nThis is **bold** text.",
+			wantErr: false,
+		},
+		{
+			name:    "empty content",
+			content: "",
+			wantErr: false,
+		},
+		{
+			name:    "complex markdown",
+			content: "# Title\n\n- List item 1\n- List item 2\n\n```go\ncode block\n```",
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := svc.ValidateContent([]byte(tt.content))
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestGenerateSnippet(t *testing.T) {
+	svc := NewService()
+
+	tests := []struct {
+		name      string
+		content   string
+		maxLength int
+		expected  string
+	}{
+		{
+			name:      "simple text",
+			content:   "Hello world",
+			maxLength: 100,
+			expected:  "Hello world",
+		},
+		{
+			name:      "text with formatting",
+			content:   "This is **bold** and *italic* text.",
+			maxLength: 100,
+			expected:  "This is bold and italic text.",
+		},
+		{
+			name:      "truncate long text",
+			content:   "This is a very long piece of text that should be truncated at a word boundary.",
+			maxLength: 30,
+			expected:  "This is a very long piece of ...",
+		},
+		{
+			name:      "heading and paragraph",
+			content:   "# My Title\n\nThis is the first paragraph.",
+			maxLength: 100,
+			expected:  "My Title This is the first paragraph.",
+		},
+		{
+			name:      "code block removed",
+			content:   "Text before\n\n```go\ncode\n```\n\nText after",
+			maxLength: 100,
+			expected:  "Text before Text after",
+		},
+		{
+			name:      "list items",
+			content:   "- Item 1\n- Item 2\n- Item 3",
+			maxLength: 100,
+			expected:  "Item 1 Item 2 Item 3",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			snippet, err := svc.GenerateSnippet([]byte(tt.content), tt.maxLength)
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, snippet)
+		})
+	}
+}
+
+func TestExtractProperties(t *testing.T) {
+	tests := []struct {
+		name     string
+		content  string
+		hasLink  bool
+		hasCode  bool
+		hasTasks bool
+		hasInc   bool
+	}{
+		{
+			name:     "plain text",
+			content:  "Just plain text",
+			hasLink:  false,
+			hasCode:  false,
+			hasTasks: false,
+			hasInc:   false,
+		},
+		{
+			name:     "with link",
+			content:  "Check out [this link](https://example.com)",
+			hasLink:  true,
+			hasCode:  false,
+			hasTasks: false,
+			hasInc:   false,
+		},
+		{
+			name:     "with inline code",
+			content:  "Use `console.log()` to debug",
+			hasLink:  false,
+			hasCode:  true,
+			hasTasks: false,
+			hasInc:   false,
+		},
+		{
+			name:     "with code block",
+			content:  "```go\nfunc main() {}\n```",
+			hasLink:  false,
+			hasCode:  true,
+			hasTasks: false,
+			hasInc:   false,
+		},
+		{
+			name:     "with completed task",
+			content:  "- [x] Completed task",
+			hasLink:  false,
+			hasCode:  false,
+			hasTasks: true,
+			hasInc:   false,
+		},
+		{
+			name:     "with incomplete task",
+			content:  "- [ ] Todo item",
+			hasLink:  false,
+			hasCode:  false,
+			hasTasks: true,
+			hasInc:   true,
+		},
+		{
+			name:     "mixed tasks",
+			content:  "- [x] Done\n- [ ] Not done",
+			hasLink:  false,
+			hasCode:  false,
+			hasTasks: true,
+			hasInc:   true,
+		},
+		{
+			name:     "everything",
+			content:  "# Title\n\n[Link](url)\n\n`code`\n\n- [ ] Task",
+			hasLink:  true,
+			hasCode:  true,
+			hasTasks: true,
+			hasInc:   true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			svc := NewService()
+
+			props, err := svc.ExtractProperties([]byte(tt.content))
+			require.NoError(t, err)
+			assert.Equal(t, tt.hasLink, props.HasLink, "HasLink")
+			assert.Equal(t, tt.hasCode, props.HasCode, "HasCode")
+			assert.Equal(t, tt.hasTasks, props.HasTaskList, "HasTaskList")
+			assert.Equal(t, tt.hasInc, props.HasIncompleteTasks, "HasIncompleteTasks")
+		})
+	}
+}
+
+func TestExtractTags(t *testing.T) {
+	tests := []struct {
+		name     string
+		content  string
+		withExt  bool
+		expected []string
+	}{
+		{
+			name:     "no tags",
+			content:  "Just plain text",
+			withExt:  false,
+			expected: []string{},
+		},
+		{
+			name:     "single tag",
+			content:  "Text with #tag",
+			withExt:  true,
+			expected: []string{"tag"},
+		},
+		{
+			name:     "multiple tags",
+			content:  "Text with #tag1 and #tag2",
+			withExt:  true,
+			expected: []string{"tag1", "tag2"},
+		},
+		{
+			name:     "duplicate tags",
+			content:  "#work is important. #Work #WORK",
+			withExt:  true,
+			expected: []string{"work", "Work", "WORK"},
+		},
+		{
+			name:     "tags with hyphens and underscores",
+			content:  "Tags: #work-notes #2024_plans",
+			withExt:  true,
+			expected: []string{"work-notes", "2024_plans"},
+		},
+		{
+			name:     "tags at end of sentence",
+			content:  "This is important #urgent.",
+			withExt:  true,
+			expected: []string{"urgent"},
+		},
+		{
+			name:     "headings not tags",
+			content:  "## Heading\n\n# Title\n\nText with #realtag",
+			withExt:  true,
+			expected: []string{"realtag"},
+		},
+		{
+			name:     "numeric tag",
+			content:  "Issue #123",
+			withExt:  true,
+			expected: []string{"123"},
+		},
+		{
+			name:     "tag in list",
+			content:  "- Item 1 #todo\n- Item 2 #done",
+			withExt:  true,
+			expected: []string{"todo", "done"},
+		},
+		{
+			name:     "no extension enabled",
+			content:  "Text with #tag",
+			withExt:  false,
+			expected: []string{},
+		},
+		{
+			name:     "Chinese tag",
+			content:  "Text with #测试",
+			withExt:  true,
+			expected: []string{"测试"},
+		},
+		{
+			name:     "Chinese tag followed by punctuation",
+			content:  "Text #测试。 More text",
+			withExt:  true,
+			expected: []string{"测试"},
+		},
+		{
+			name:     "mixed Chinese and ASCII tag",
+			content:  "#测试test123 content",
+			withExt:  true,
+			expected: []string{"测试test123"},
+		},
+		{
+			name:     "Japanese tag",
+			content:  "#日本語 content",
+			withExt:  true,
+			expected: []string{"日本語"},
+		},
+		{
+			name:     "Korean tag",
+			content:  "#한국어 content",
+			withExt:  true,
+			expected: []string{"한국어"},
+		},
+		{
+			name:     "hierarchical tag with Chinese",
+			content:  "#work/测试/项目",
+			withExt:  true,
+			expected: []string{"work/测试/项目"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var svc Service
+			if tt.withExt {
+				svc = NewService(WithTagExtension())
+			} else {
+				svc = NewService()
+			}
+
+			tags, err := svc.ExtractTags([]byte(tt.content))
+			require.NoError(t, err)
+			assert.ElementsMatch(t, tt.expected, tags)
+		})
+	}
+}
+
+func TestUniquePreserveCase(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    []string
+		expected []string
+	}{
+		{
+			name:     "empty",
+			input:    []string{},
+			expected: []string{},
+		},
+		{
+			name:     "unique items",
+			input:    []string{"tag1", "tag2", "tag3"},
+			expected: []string{"tag1", "tag2", "tag3"},
+		},
+		{
+			name:     "duplicates",
+			input:    []string{"tag", "TAG", "Tag"},
+			expected: []string{"tag", "TAG", "Tag"},
+		},
+		{
+			name:     "mixed",
+			input:    []string{"Work", "work", "Important", "work"},
+			expected: []string{"Work", "work", "Important"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := uniquePreserveCase(tt.input)
+			assert.ElementsMatch(t, tt.expected, result)
+		})
+	}
+}
+
+func TestTruncateAtWord(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		maxLength int
+		expected  string
+	}{
+		{
+			name:      "no truncation needed",
+			input:     "short",
+			maxLength: 10,
+			expected:  "short",
+		},
+		{
+			name:      "exact length",
+			input:     "exactly ten",
+			maxLength: 11,
+			expected:  "exactly ten",
+		},
+		{
+			name:      "truncate at word",
+			input:     "this is a long sentence",
+			maxLength: 10,
+			expected:  "this is a ...",
+		},
+		{
+			name:      "truncate very long word",
+			input:     "supercalifragilisticexpialidocious",
+			maxLength: 10,
+			expected:  "supercalif ...",
+		},
+		{
+			name:      "CJK characters without spaces",
+			input:     "这是一个很长的中文句子没有空格的情况下也要正确处理",
+			maxLength: 15,
+			expected:  "这是一个很长的中文句子没有空格 ...",
+		},
+		{
+			name:      "mixed CJK and Latin",
+			input:     "这是中文mixed with English文字",
+			maxLength: 10,
+			expected:  "这是中文mixed ...",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := truncateAtWord(tt.input, tt.maxLength)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// Benchmark tests.
+func BenchmarkGenerateSnippet(b *testing.B) {
+	svc := NewService()
+	content := []byte(`# Large Document
+
+This is a large document with multiple paragraphs and formatting.
+
+## Section 1
+
+Here is some **bold** text and *italic* text with [links](https://example.com).
+
+- List item 1
+- List item 2
+- List item 3
+
+## Section 2
+
+More content here with ` + "`inline code`" + ` and other elements.
+
+` + "```go\nfunc example() {\n    return true\n}\n```")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := svc.GenerateSnippet(content, 200)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func BenchmarkExtractProperties(b *testing.B) {
+	svc := NewService()
+	content := []byte("# Title\n\n[Link](url)\n\n`code`\n\n- [ ] Task\n- [x] Done")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := svc.ExtractProperties(content)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}

plugin/markdown/parser/tag.go

@@ -0,0 +1,139 @@
+package parser
+
+import (
+	"unicode"
+	"unicode/utf8"
+
+	gast "github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+
+	mast "github.com/usememos/memos/plugin/markdown/ast"
+)
+
+const (
+	// MaxTagLength defines the maximum number of runes allowed in a tag.
+	MaxTagLength = 100
+)
+
+type tagParser struct{}
+
+// NewTagParser creates a new inline parser for #tag syntax.
+func NewTagParser() parser.InlineParser {
+	return &tagParser{}
+}
+
+// Trigger returns the characters that trigger this parser.
+func (*tagParser) Trigger() []byte {
+	return []byte{'#'}
+}
+
+// isValidTagRune checks if a Unicode rune is valid in a tag.
+// Uses Unicode categories for proper international character support.
+func isValidTagRune(r rune) bool {
+	// Allow Unicode letters (any script: Latin, CJK, Arabic, Cyrillic, etc.)
+	if unicode.IsLetter(r) {
+		return true
+	}
+
+	// Allow Unicode digits
+	if unicode.IsNumber(r) {
+		return true
+	}
+
+	// Allow emoji and symbols (So category: Symbol, Other)
+	// This includes emoji, which are essential for social media-style tagging
+	if unicode.IsSymbol(r) {
+		return true
+	}
+
+	// Allow specific ASCII symbols for tag structure
+	// Underscore: word separation (snake_case)
+	// Hyphen: word separation (kebab-case)
+	// Forward slash: hierarchical tags (category/subcategory)
+	// Ampersand: compound tags (science&tech)
+	if r == '_' || r == '-' || r == '/' || r == '&' {
+		return true
+	}
+
+	return false
+}
+
+// Parse parses #tag syntax using Unicode-aware validation.
+// Tags support international characters and follow these rules:
+//   - Must start with # followed by valid tag characters
+//   - Valid characters: Unicode letters, Unicode digits, underscore (_), hyphen (-), forward slash (/)
+//   - Maximum length: 100 runes (Unicode characters)
+//   - Stops at: whitespace, punctuation, or other invalid characters
+func (*tagParser) Parse(_ gast.Node, block text.Reader, _ parser.Context) gast.Node {
+	line, _ := block.PeekLine()
+
+	// Must start with #
+	if len(line) == 0 || line[0] != '#' {
+		return nil
+	}
+
+	// Check if it's a heading (## or space after #)
+	if len(line) > 1 {
+		if line[1] == '#' {
+			// It's a heading (##), not a tag
+			return nil
+		}
+		if line[1] == ' ' {
+			// Space after # - heading or just a hash
+			return nil
+		}
+	} else {
+		// Just a lone #
+		return nil
+	}
+
+	// Parse tag using UTF-8 aware rune iteration
+	tagStart := 1
+	pos := tagStart
+	runeCount := 0
+
+	for pos < len(line) {
+		r, size := utf8.DecodeRune(line[pos:])
+
+		// Stop at invalid UTF-8
+		if r == utf8.RuneError && size == 1 {
+			break
+		}
+
+		// Validate character using Unicode categories
+		if !isValidTagRune(r) {
+			break
+		}
+
+		// Enforce max length (by rune count, not byte count)
+		runeCount++
+		if runeCount > MaxTagLength {
+			break
+		}
+
+		pos += size
+	}
+
+	// Must have at least one character after #
+	if pos <= tagStart {
+		return nil
+	}
+
+	// Extract tag (without #)
+	tagName := line[tagStart:pos]
+
+	// Make a copy of the tag name
+	tagCopy := make([]byte, len(tagName))
+	copy(tagCopy, tagName)
+
+	// Advance reader
+	block.Advance(pos)
+
+	// Create node
+	node := &mast.TagNode{
+		Tag: tagCopy,
+	}
+
+	return node
+}

plugin/markdown/parser/tag_test.go

@@ -0,0 +1,251 @@
+package parser
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+
+	mast "github.com/usememos/memos/plugin/markdown/ast"
+)
+
+func TestTagParser(t *testing.T) {
+	tests := []struct {
+		name        string
+		input       string
+		expectedTag string
+		shouldParse bool
+	}{
+		{
+			name:        "basic tag",
+			input:       "#tag",
+			expectedTag: "tag",
+			shouldParse: true,
+		},
+		{
+			name:        "tag with hyphen",
+			input:       "#work-notes",
+			expectedTag: "work-notes",
+			shouldParse: true,
+		},
+		{
+			name:        "tag with ampersand",
+			input:       "#science&tech",
+			expectedTag: "science&tech",
+			shouldParse: true,
+		},
+		{
+			name:        "tag with underscore",
+			input:       "#2024_plans",
+			expectedTag: "2024_plans",
+			shouldParse: true,
+		},
+		{
+			name:        "numeric tag",
+			input:       "#123",
+			expectedTag: "123",
+			shouldParse: true,
+		},
+		{
+			name:        "tag followed by space",
+			input:       "#tag ",
+			expectedTag: "tag",
+			shouldParse: true,
+		},
+		{
+			name:        "tag followed by punctuation",
+			input:       "#tag.",
+			expectedTag: "tag",
+			shouldParse: true,
+		},
+		{
+			name:        "tag in sentence",
+			input:       "#important task",
+			expectedTag: "important",
+			shouldParse: true,
+		},
+		{
+			name:        "heading (##)",
+			input:       "## Heading",
+			expectedTag: "",
+			shouldParse: false,
+		},
+		{
+			name:        "space after hash",
+			input:       "# heading",
+			expectedTag: "",
+			shouldParse: false,
+		},
+		{
+			name:        "lone hash",
+			input:       "#",
+			expectedTag: "",
+			shouldParse: false,
+		},
+		{
+			name:        "hash with space",
+			input:       "# ",
+			expectedTag: "",
+			shouldParse: false,
+		},
+		{
+			name:        "special characters",
+			input:       "#tag@special",
+			expectedTag: "tag",
+			shouldParse: true,
+		},
+		{
+			name:        "mixed case",
+			input:       "#WorkNotes",
+			expectedTag: "WorkNotes",
+			shouldParse: true,
+		},
+		{
+			name:        "hierarchical tag with slash",
+			input:       "#tag1/subtag",
+			expectedTag: "tag1/subtag",
+			shouldParse: true,
+		},
+		{
+			name:        "hierarchical tag with multiple levels",
+			input:       "#tag1/subtag/subtag2",
+			expectedTag: "tag1/subtag/subtag2",
+			shouldParse: true,
+		},
+		{
+			name:        "hierarchical tag followed by space",
+			input:       "#work/notes ",
+			expectedTag: "work/notes",
+			shouldParse: true,
+		},
+		{
+			name:        "hierarchical tag followed by punctuation",
+			input:       "#project/2024.",
+			expectedTag: "project/2024",
+			shouldParse: true,
+		},
+		{
+			name:        "hierarchical tag with numbers and dashes",
+			input:       "#work-log/2024/q1",
+			expectedTag: "work-log/2024/q1",
+			shouldParse: true,
+		},
+		{
+			name:        "Chinese characters",
+			input:       "#测试",
+			expectedTag: "测试",
+			shouldParse: true,
+		},
+		{
+			name:        "Chinese tag followed by space",
+			input:       "#测试 some text",
+			expectedTag: "测试",
+			shouldParse: true,
+		},
+		{
+			name:        "Chinese tag followed by punctuation",
+			input:       "#测试。",
+			expectedTag: "测试",
+			shouldParse: true,
+		},
+		{
+			name:        "mixed Chinese and ASCII",
+			input:       "#测试test123",
+			expectedTag: "测试test123",
+			shouldParse: true,
+		},
+		{
+			name:        "Japanese characters",
+			input:       "#テスト",
+			expectedTag: "テスト",
+			shouldParse: true,
+		},
+		{
+			name:        "Korean characters",
+			input:       "#테스트",
+			expectedTag: "테스트",
+			shouldParse: true,
+		},
+		{
+			name:        "emoji",
+			input:       "#test🚀",
+			expectedTag: "test🚀",
+			shouldParse: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := NewTagParser()
+			reader := text.NewReader([]byte(tt.input))
+			ctx := parser.NewContext()
+
+			node := p.Parse(nil, reader, ctx)
+
+			if tt.shouldParse {
+				require.NotNil(t, node, "Expected tag to be parsed")
+				require.IsType(t, &mast.TagNode{}, node)
+
+				tagNode, ok := node.(*mast.TagNode)
+				require.True(t, ok, "Expected node to be *mast.TagNode")
+				assert.Equal(t, tt.expectedTag, string(tagNode.Tag))
+			} else {
+				assert.Nil(t, node, "Expected tag NOT to be parsed")
+			}
+		})
+	}
+}
+
+func TestTagParser_Trigger(t *testing.T) {
+	p := NewTagParser()
+	triggers := p.Trigger()
+
+	assert.Equal(t, []byte{'#'}, triggers)
+}
+
+func TestTagParser_MultipleTags(t *testing.T) {
+	// Test that parser correctly handles multiple tags in sequence
+	input := "#tag1 #tag2"
+
+	p := NewTagParser()
+	reader := text.NewReader([]byte(input))
+	ctx := parser.NewContext()
+
+	// Parse first tag
+	node1 := p.Parse(nil, reader, ctx)
+	require.NotNil(t, node1)
+	tagNode1, ok := node1.(*mast.TagNode)
+	require.True(t, ok, "Expected node1 to be *mast.TagNode")
+	assert.Equal(t, "tag1", string(tagNode1.Tag))
+
+	// Advance past the space
+	reader.Advance(1)
+
+	// Parse second tag
+	node2 := p.Parse(nil, reader, ctx)
+	require.NotNil(t, node2)
+	tagNode2, ok := node2.(*mast.TagNode)
+	require.True(t, ok, "Expected node2 to be *mast.TagNode")
+	assert.Equal(t, "tag2", string(tagNode2.Tag))
+}
+
+func TestTagNode_Kind(t *testing.T) {
+	node := &mast.TagNode{
+		Tag: []byte("test"),
+	}
+
+	assert.Equal(t, mast.KindTag, node.Kind())
+}
+
+func TestTagNode_Dump(t *testing.T) {
+	node := &mast.TagNode{
+		Tag: []byte("test"),
+	}
+
+	// Should not panic
+	assert.NotPanics(t, func() {
+		node.Dump([]byte("#test"), 0)
+	})
+}

plugin/markdown/renderer/markdown_renderer.go

@@ -0,0 +1,266 @@
+package renderer
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+
+	gast "github.com/yuin/goldmark/ast"
+	east "github.com/yuin/goldmark/extension/ast"
+
+	mast "github.com/usememos/memos/plugin/markdown/ast"
+)
+
+// MarkdownRenderer renders goldmark AST back to markdown text.
+type MarkdownRenderer struct {
+	buf *bytes.Buffer
+}
+
+// NewMarkdownRenderer creates a new markdown renderer.
+func NewMarkdownRenderer() *MarkdownRenderer {
+	return &MarkdownRenderer{
+		buf: &bytes.Buffer{},
+	}
+}
+
+// Render renders the AST node to markdown and returns the result.
+func (r *MarkdownRenderer) Render(node gast.Node, source []byte) string {
+	r.buf.Reset()
+	r.renderNode(node, source, 0)
+	return r.buf.String()
+}
+
+// renderNode renders a single node and its children.
+func (r *MarkdownRenderer) renderNode(node gast.Node, source []byte, depth int) {
+	switch n := node.(type) {
+	case *gast.Document:
+		r.renderChildren(n, source, depth)
+
+	case *gast.Paragraph:
+		r.renderChildren(n, source, depth)
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	case *gast.Text:
+		// Text nodes store their content as segments in the source
+		segment := n.Segment
+		r.buf.Write(segment.Value(source))
+		if n.SoftLineBreak() {
+			r.buf.WriteByte('\n')
+		} else if n.HardLineBreak() {
+			r.buf.WriteString("  \n")
+		}
+
+	case *gast.CodeSpan:
+		r.buf.WriteByte('`')
+		r.renderChildren(n, source, depth)
+		r.buf.WriteByte('`')
+
+	case *gast.Emphasis:
+		symbol := "*"
+		if n.Level == 2 {
+			symbol = "**"
+		}
+		r.buf.WriteString(symbol)
+		r.renderChildren(n, source, depth)
+		r.buf.WriteString(symbol)
+
+	case *gast.Link:
+		r.buf.WriteString("[")
+		r.renderChildren(n, source, depth)
+		r.buf.WriteString("](")
+		r.buf.Write(n.Destination)
+		if len(n.Title) > 0 {
+			r.buf.WriteString(` "`)
+			r.buf.Write(n.Title)
+			r.buf.WriteString(`"`)
+		}
+		r.buf.WriteString(")")
+
+	case *gast.AutoLink:
+		url := n.URL(source)
+		if n.AutoLinkType == gast.AutoLinkEmail {
+			r.buf.WriteString("<")
+			r.buf.Write(url)
+			r.buf.WriteString(">")
+		} else {
+			r.buf.Write(url)
+		}
+
+	case *gast.Image:
+		r.buf.WriteString("![")
+		r.renderChildren(n, source, depth)
+		r.buf.WriteString("](")
+		r.buf.Write(n.Destination)
+		if len(n.Title) > 0 {
+			r.buf.WriteString(` "`)
+			r.buf.Write(n.Title)
+			r.buf.WriteString(`"`)
+		}
+		r.buf.WriteString(")")
+
+	case *gast.Heading:
+		r.buf.WriteString(strings.Repeat("#", n.Level))
+		r.buf.WriteByte(' ')
+		r.renderChildren(n, source, depth)
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	case *gast.CodeBlock, *gast.FencedCodeBlock:
+		r.renderCodeBlock(n, source)
+
+	case *gast.Blockquote:
+		// Render each child line with "> " prefix
+		r.renderBlockquote(n, source, depth)
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	case *gast.List:
+		r.renderChildren(n, source, depth)
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	case *gast.ListItem:
+		r.renderListItem(n, source, depth)
+
+	case *gast.ThematicBreak:
+		r.buf.WriteString("---")
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	case *east.Strikethrough:
+		r.buf.WriteString("~~")
+		r.renderChildren(n, source, depth)
+		r.buf.WriteString("~~")
+
+	case *east.TaskCheckBox:
+		if n.IsChecked {
+			r.buf.WriteString("[x] ")
+		} else {
+			r.buf.WriteString("[ ] ")
+		}
+
+	case *east.Table:
+		r.renderTable(n, source)
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+
+	// Custom Memos nodes
+	case *mast.TagNode:
+		r.buf.WriteByte('#')
+		r.buf.Write(n.Tag)
+
+	default:
+		// For unknown nodes, try to render children
+		r.renderChildren(n, source, depth)
+	}
+}
+
+// renderChildren renders all children of a node.
+func (r *MarkdownRenderer) renderChildren(node gast.Node, source []byte, depth int) {
+	child := node.FirstChild()
+	for child != nil {
+		r.renderNode(child, source, depth+1)
+		child = child.NextSibling()
+	}
+}
+
+// renderCodeBlock renders a code block.
+func (r *MarkdownRenderer) renderCodeBlock(node gast.Node, source []byte) {
+	if fenced, ok := node.(*gast.FencedCodeBlock); ok {
+		// Fenced code block with language
+		r.buf.WriteString("```")
+		if lang := fenced.Language(source); len(lang) > 0 {
+			r.buf.Write(lang)
+		}
+		r.buf.WriteByte('\n')
+
+		// Write all lines
+		lines := fenced.Lines()
+		for i := 0; i < lines.Len(); i++ {
+			line := lines.At(i)
+			r.buf.Write(line.Value(source))
+		}
+
+		r.buf.WriteString("```")
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+	} else if codeBlock, ok := node.(*gast.CodeBlock); ok {
+		// Indented code block
+		lines := codeBlock.Lines()
+		for i := 0; i < lines.Len(); i++ {
+			line := lines.At(i)
+			r.buf.WriteString("    ")
+			r.buf.Write(line.Value(source))
+		}
+		if node.NextSibling() != nil {
+			r.buf.WriteString("\n\n")
+		}
+	}
+}
+
+// renderBlockquote renders a blockquote with "> " prefix.
+func (r *MarkdownRenderer) renderBlockquote(node *gast.Blockquote, source []byte, depth int) {
+	// Create a temporary buffer for the blockquote content
+	tempBuf := &bytes.Buffer{}
+	tempRenderer := &MarkdownRenderer{buf: tempBuf}
+	tempRenderer.renderChildren(node, source, depth)
+
+	// Add "> " prefix to each line
+	content := tempBuf.String()
+	lines := strings.Split(strings.TrimRight(content, "\n"), "\n")
+	for i, line := range lines {
+		r.buf.WriteString("> ")
+		r.buf.WriteString(line)
+		if i < len(lines)-1 {
+			r.buf.WriteByte('\n')
+		}
+	}
+}
+
+// renderListItem renders a list item with proper indentation and markers.
+func (r *MarkdownRenderer) renderListItem(node *gast.ListItem, source []byte, depth int) {
+	parent := node.Parent()
+	list, ok := parent.(*gast.List)
+	if !ok {
+		r.renderChildren(node, source, depth)
+		return
+	}
+
+	// Add indentation only for nested lists
+	// Document=0, List=1, ListItem=2 (no indent), nested ListItem=3+ (indent)
+	if depth > 2 {
+		indent := strings.Repeat("  ", depth-2)
+		r.buf.WriteString(indent)
+	}
+
+	// Add list marker
+	if list.IsOrdered() {
+		fmt.Fprintf(r.buf, "%d. ", list.Start)
+		list.Start++ // Increment for next item
+	} else {
+		r.buf.WriteString("- ")
+	}
+
+	// Render content
+	r.renderChildren(node, source, depth)
+
+	// Add newline if there's a next sibling
+	if node.NextSibling() != nil {
+		r.buf.WriteByte('\n')
+	}
+}
+
+// renderTable renders a table in markdown format.
+func (r *MarkdownRenderer) renderTable(table *east.Table, source []byte) {
+	// This is a simplified table renderer
+	// A full implementation would need to handle alignment, etc.
+	r.renderChildren(table, source, 0)
+}

plugin/markdown/renderer/markdown_renderer_test.go

@@ -0,0 +1,176 @@
+package renderer
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/extension"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+
+	"github.com/usememos/memos/plugin/markdown/extensions"
+)
+
+func TestMarkdownRenderer(t *testing.T) {
+	// Create goldmark instance with all extensions
+	md := goldmark.New(
+		goldmark.WithExtensions(
+			extension.GFM,
+			extensions.TagExtension,
+		),
+		goldmark.WithParserOptions(
+			parser.WithAutoHeadingID(),
+		),
+	)
+
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "simple text",
+			input:    "Hello world",
+			expected: "Hello world",
+		},
+		{
+			name:     "paragraph with newlines",
+			input:    "First paragraph\n\nSecond paragraph",
+			expected: "First paragraph\n\nSecond paragraph",
+		},
+		{
+			name:     "emphasis",
+			input:    "This is *italic* and **bold** text",
+			expected: "This is *italic* and **bold** text",
+		},
+		{
+			name:     "headings",
+			input:    "# Heading 1\n\n## Heading 2\n\n### Heading 3",
+			expected: "# Heading 1\n\n## Heading 2\n\n### Heading 3",
+		},
+		{
+			name:     "link",
+			input:    "Check [this link](https://example.com)",
+			expected: "Check [this link](https://example.com)",
+		},
+		{
+			name:     "image",
+			input:    "![alt text](image.png)",
+			expected: "![alt text](image.png)",
+		},
+		{
+			name:     "code inline",
+			input:    "This is `inline code` here",
+			expected: "This is `inline code` here",
+		},
+		{
+			name:     "code block fenced",
+			input:    "```go\nfunc main() {\n}\n```",
+			expected: "```go\nfunc main() {\n}\n```",
+		},
+		{
+			name:     "unordered list",
+			input:    "- Item 1\n- Item 2\n- Item 3",
+			expected: "- Item 1\n- Item 2\n- Item 3",
+		},
+		{
+			name:     "ordered list",
+			input:    "1. First\n2. Second\n3. Third",
+			expected: "1. First\n2. Second\n3. Third",
+		},
+		{
+			name:     "blockquote",
+			input:    "> This is a quote\n> Second line",
+			expected: "> This is a quote\n> Second line",
+		},
+		{
+			name:     "horizontal rule",
+			input:    "Text before\n\n---\n\nText after",
+			expected: "Text before\n\n---\n\nText after",
+		},
+		{
+			name:     "strikethrough",
+			input:    "This is ~~deleted~~ text",
+			expected: "This is ~~deleted~~ text",
+		},
+		{
+			name:     "task list",
+			input:    "- [x] Completed task\n- [ ] Incomplete task",
+			expected: "- [x] Completed task\n- [ ] Incomplete task",
+		},
+		{
+			name:     "tag",
+			input:    "This has #tag in it",
+			expected: "This has #tag in it",
+		},
+		{
+			name:     "multiple tags",
+			input:    "#work #important meeting notes",
+			expected: "#work #important meeting notes",
+		},
+		{
+			name:     "complex mixed content",
+			input:    "# Meeting Notes\n\n**Date**: 2024-01-01\n\n## Attendees\n- Alice\n- Bob\n\n## Discussion\n\nWe discussed #project status.\n\n```python\nprint('hello')\n```",
+			expected: "# Meeting Notes\n\n**Date**: 2024-01-01\n\n## Attendees\n\n- Alice\n- Bob\n\n## Discussion\n\nWe discussed #project status.\n\n```python\nprint('hello')\n```",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Parse the input
+			source := []byte(tt.input)
+			reader := text.NewReader(source)
+			doc := md.Parser().Parse(reader)
+			require.NotNil(t, doc)
+
+			// Render back to markdown
+			renderer := NewMarkdownRenderer()
+			result := renderer.Render(doc, source)
+
+			// For debugging
+			if result != tt.expected {
+				t.Logf("Input:    %q", tt.input)
+				t.Logf("Expected: %q", tt.expected)
+				t.Logf("Got:      %q", result)
+			}
+
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func TestMarkdownRendererPreservesStructure(t *testing.T) {
+	// Test that parsing and rendering preserves structure
+	md := goldmark.New(
+		goldmark.WithExtensions(
+			extension.GFM,
+			extensions.TagExtension,
+		),
+	)
+
+	inputs := []string{
+		"# Title\n\nParagraph",
+		"**Bold** and *italic*",
+		"- List\n- Items",
+		"#tag #another",
+		"> Quote",
+	}
+
+	renderer := NewMarkdownRenderer()
+
+	for _, input := range inputs {
+		t.Run(input, func(t *testing.T) {
+			source := []byte(input)
+			reader := text.NewReader(source)
+			doc := md.Parser().Parse(reader)
+
+			result := renderer.Render(doc, source)
+
+			// The result should be structurally similar
+			// (may have minor formatting differences)
+			assert.NotEmpty(t, result)
+		})
+	}
+}

plugin/scheduler/README.md

@@ -0,0 +1,367 @@
+# Scheduler Plugin
+
+A production-ready, GitHub Actions-inspired cron job scheduler for Go.
+
+## Features
+
+- **Standard Cron Syntax**: Supports both 5-field and 6-field (with seconds) cron expressions
+- **Timezone-Aware**: Explicit timezone handling to avoid DST surprises
+- **Middleware Pattern**: Composable job wrappers for logging, metrics, panic recovery, timeouts
+- **Graceful Shutdown**: Jobs complete cleanly or cancel when context expires
+- **Zero Dependencies**: Core functionality uses only the standard library
+- **Type-Safe**: Strong typing with clear error messages
+- **Well-Tested**: Comprehensive test coverage
+
+## Installation
+
+This package is included with Memos. No separate installation required.
+
+## Quick Start
+
+```go
+package main
+
+import (
+    "context"
+    "fmt"
+    "github.com/usememos/memos/plugin/scheduler"
+)
+
+func main() {
+    s := scheduler.New()
+
+    s.Register(&scheduler.Job{
+        Name:     "daily-cleanup",
+        Schedule: "0 2 * * *", // 2 AM daily
+        Handler: func(ctx context.Context) error {
+            fmt.Println("Running cleanup...")
+            return nil
+        },
+    })
+
+    s.Start()
+    defer s.Stop(context.Background())
+
+    // Keep running...
+    select {}
+}
+```
+
+## Cron Expression Format
+
+### 5-Field Format (Standard)
+```
+┌───────────── minute (0 - 59)
+│ ┌───────────── hour (0 - 23)
+│ │ ┌───────────── day of month (1 - 31)
+│ │ │ ┌───────────── month (1 - 12)
+│ │ │ │ ┌───────────── day of week (0 - 7) (Sunday = 0 or 7)
+│ │ │ │ │
+* * * * *
+```
+
+### 6-Field Format (With Seconds)
+```
+┌───────────── second (0 - 59)
+│ ┌───────────── minute (0 - 59)
+│ │ ┌───────────── hour (0 - 23)
+│ │ │ ┌───────────── day of month (1 - 31)
+│ │ │ │ ┌───────────── month (1 - 12)
+│ │ │ │ │ ┌───────────── day of week (0 - 7)
+│ │ │ │ │ │
+* * * * * *
+```
+
+### Special Characters
+
+- `*` - Any value (every minute, every hour, etc.)
+- `,` - List of values: `1,15,30` (1st, 15th, and 30th)
+- `-` - Range: `9-17` (9 AM through 5 PM)
+- `/` - Step: `*/15` (every 15 units)
+
+### Common Examples
+
+| Schedule | Description |
+|----------|-------------|
+| `* * * * *` | Every minute |
+| `0 * * * *` | Every hour |
+| `0 0 * * *` | Daily at midnight |
+| `0 9 * * 1-5` | Weekdays at 9 AM |
+| `*/15 * * * *` | Every 15 minutes |
+| `0 0 1 * *` | First day of every month |
+| `0 0 * * 0` | Every Sunday at midnight |
+| `30 14 * * *` | Every day at 2:30 PM |
+
+## Timezone Support
+
+```go
+// Global timezone for all jobs
+s := scheduler.New(
+    scheduler.WithTimezone("America/New_York"),
+)
+
+// Per-job timezone (overrides global)
+s.Register(&scheduler.Job{
+    Name:     "tokyo-report",
+    Schedule: "0 9 * * *", // 9 AM Tokyo time
+    Timezone: "Asia/Tokyo",
+    Handler: func(ctx context.Context) error {
+        // Runs at 9 AM in Tokyo
+        return nil
+    },
+})
+```
+
+**Important**: Always use IANA timezone names (`America/New_York`, not `EST`).
+
+## Middleware
+
+Middleware wraps job handlers to add cross-cutting behavior. Multiple middleware can be chained together.
+
+### Built-in Middleware
+
+#### Recovery (Panic Handling)
+
+```go
+s := scheduler.New(
+    scheduler.WithMiddleware(
+        scheduler.Recovery(func(jobName string, r interface{}) {
+            log.Printf("Job %s panicked: %v", jobName, r)
+        }),
+    ),
+)
+```
+
+#### Logging
+
+```go
+type Logger interface {
+    Info(msg string, args ...interface{})
+    Error(msg string, args ...interface{})
+}
+
+s := scheduler.New(
+    scheduler.WithMiddleware(
+        scheduler.Logging(myLogger),
+    ),
+)
+```
+
+#### Timeout
+
+```go
+s := scheduler.New(
+    scheduler.WithMiddleware(
+        scheduler.Timeout(5 * time.Minute),
+    ),
+)
+```
+
+### Combining Middleware
+
+```go
+s := scheduler.New(
+    scheduler.WithMiddleware(
+        scheduler.Recovery(panicHandler),
+        scheduler.Logging(logger),
+        scheduler.Timeout(10 * time.Minute),
+    ),
+)
+```
+
+**Order matters**: Middleware are applied left-to-right. In the example above:
+1. Recovery (outermost) catches panics from everything
+2. Logging logs the execution
+3. Timeout (innermost) wraps the actual handler
+
+### Custom Middleware
+
+```go
+func Metrics(recorder MetricsRecorder) scheduler.Middleware {
+    return func(next scheduler.JobHandler) scheduler.JobHandler {
+        return func(ctx context.Context) error {
+            start := time.Now()
+            err := next(ctx)
+            duration := time.Since(start)
+
+            jobName := scheduler.GetJobName(ctx)
+            recorder.Record(jobName, duration, err)
+
+            return err
+        }
+    }
+}
+```
+
+## Graceful Shutdown
+
+Always use `Stop()` with a context to allow jobs to finish cleanly:
+
+```go
+// Give jobs up to 30 seconds to complete
+ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+defer cancel()
+
+if err := s.Stop(ctx); err != nil {
+    log.Printf("Shutdown error: %v", err)
+}
+```
+
+Jobs should respect context cancellation:
+
+```go
+Handler: func(ctx context.Context) error {
+    for i := 0; i < 100; i++ {
+        select {
+        case <-ctx.Done():
+            return ctx.Err() // Canceled
+        default:
+            // Do work
+        }
+    }
+    return nil
+}
+```
+
+## Best Practices
+
+### 1. Always Name Your Jobs
+
+Names are used for logging, metrics, and debugging:
+
+```go
+Name: "user-cleanup-job" // Good
+Name: "job1"             // Bad
+```
+
+### 2. Add Descriptions and Tags
+
+```go
+s.Register(&scheduler.Job{
+    Name:        "stale-session-cleanup",
+    Description: "Removes user sessions older than 30 days",
+    Tags:        []string{"maintenance", "security"},
+    Schedule:    "0 3 * * *",
+    Handler:     cleanupSessions,
+})
+```
+
+### 3. Use Appropriate Middleware
+
+Always include Recovery and Logging in production:
+
+```go
+scheduler.New(
+    scheduler.WithMiddleware(
+        scheduler.Recovery(logPanic),
+        scheduler.Logging(logger),
+    ),
+)
+```
+
+### 4. Avoid Scheduling Exactly on the Hour
+
+Many systems schedule jobs at `:00`, causing load spikes. Stagger your jobs:
+
+```go
+"5 2 * * *"  // 2:05 AM (good)
+"0 2 * * *"  // 2:00 AM (often overloaded)
+```
+
+### 5. Make Jobs Idempotent
+
+Jobs may run multiple times (crash recovery, etc.). Design them to be safely re-runnable:
+
+```go
+Handler: func(ctx context.Context) error {
+    // Use unique constraint or check-before-insert
+    db.Exec("INSERT IGNORE INTO processed_items ...")
+    return nil
+}
+```
+
+### 6. Handle Timezones Explicitly
+
+Always specify timezone for business-hour jobs:
+
+```go
+Timezone: "America/New_York" // Good
+// Timezone: ""              // Bad (defaults to UTC)
+```
+
+### 7. Test Your Cron Expressions
+
+Use a cron expression calculator before deploying:
+- [crontab.guru](https://crontab.guru/)
+- Write unit tests with the parser
+
+## Testing Jobs
+
+Test job handlers independently of the scheduler:
+
+```go
+func TestCleanupJob(t *testing.T) {
+    ctx := context.Background()
+
+    err := cleanupHandler(ctx)
+    if err != nil {
+        t.Fatalf("cleanup failed: %v", err)
+    }
+
+    // Verify cleanup occurred
+}
+```
+
+Test schedule parsing:
+
+```go
+func TestScheduleParsing(t *testing.T) {
+    job := &scheduler.Job{
+        Name:     "test",
+        Schedule: "0 2 * * *",
+        Handler:  func(ctx context.Context) error { return nil },
+    }
+
+    if err := job.Validate(); err != nil {
+        t.Fatalf("invalid job: %v", err)
+    }
+}
+```
+
+## Comparison to Other Solutions
+
+| Feature | scheduler | robfig/cron | github.com/go-co-op/gocron |
+|---------|-----------|-------------|----------------------------|
+| Standard cron syntax | ✅ | ✅ | ✅ |
+| Seconds support | ✅ | ✅ | ✅ |
+| Timezone support | ✅ | ✅ | ✅ |
+| Middleware pattern | ✅ | ⚠️ (basic) | ❌ |
+| Graceful shutdown | ✅ | ⚠️ (basic) | ✅ |
+| Zero dependencies | ✅ | ❌ | ❌ |
+| Job metadata | ✅ | ❌ | ⚠️ (limited) |
+
+## API Reference
+
+See [example_test.go](./example_test.go) for comprehensive examples.
+
+### Core Types
+
+- `Scheduler` - Manages scheduled jobs
+- `Job` - Job definition with schedule and handler
+- `Middleware` - Function that wraps job handlers
+
+### Functions
+
+- `New(opts ...Option) *Scheduler` - Create new scheduler
+- `WithTimezone(tz string) Option` - Set default timezone
+- `WithMiddleware(mw ...Middleware) Option` - Add middleware
+
+### Methods
+
+- `Register(job *Job) error` - Add job to scheduler
+- `Start() error` - Begin executing jobs
+- `Stop(ctx context.Context) error` - Graceful shutdown
+
+## License
+
+This package is part of the Memos project and shares its license.

plugin/scheduler/doc.go

@@ -0,0 +1,35 @@
+// Package scheduler provides a GitHub Actions-inspired cron job scheduler.
+//
+// Features:
+//   - Standard cron expression syntax (5-field and 6-field formats)
+//   - Timezone-aware scheduling
+//   - Middleware pattern for cross-cutting concerns (logging, metrics, recovery)
+//   - Graceful shutdown with context cancellation
+//   - Zero external dependencies
+//
+// Basic usage:
+//
+//	s := scheduler.New()
+//
+//	s.Register(&scheduler.Job{
+//		Name:     "daily-cleanup",
+//		Schedule: "0 2 * * *", // 2 AM daily
+//		Handler: func(ctx context.Context) error {
+//			// Your cleanup logic here
+//			return nil
+//		},
+//	})
+//
+//	s.Start()
+//	defer s.Stop(context.Background())
+//
+// With middleware:
+//
+//	s := scheduler.New(
+//		scheduler.WithTimezone("America/New_York"),
+//		scheduler.WithMiddleware(
+//			scheduler.Recovery(),
+//			scheduler.Logging(),
+//		),
+//	)
+package scheduler

plugin/scheduler/example_test.go

@@ -0,0 +1,165 @@
+package scheduler_test
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"time"
+
+	"github.com/usememos/memos/plugin/scheduler"
+)
+
+// Example demonstrates basic scheduler usage.
+func Example_basic() {
+	s := scheduler.New()
+
+	s.Register(&scheduler.Job{
+		Name:        "hello",
+		Schedule:    "*/5 * * * *", // Every 5 minutes
+		Description: "Say hello",
+		Handler: func(_ context.Context) error {
+			fmt.Println("Hello from scheduler!")
+			return nil
+		},
+	})
+
+	s.Start()
+	defer s.Stop(context.Background())
+
+	// Scheduler runs in background
+	time.Sleep(100 * time.Millisecond)
+}
+
+// Example demonstrates timezone-aware scheduling.
+func Example_timezone() {
+	s := scheduler.New(
+		scheduler.WithTimezone("America/New_York"),
+	)
+
+	s.Register(&scheduler.Job{
+		Name:     "daily-report",
+		Schedule: "0 9 * * *", // 9 AM in New York
+		Handler: func(_ context.Context) error {
+			fmt.Println("Generating daily report...")
+			return nil
+		},
+	})
+
+	s.Start()
+	defer s.Stop(context.Background())
+}
+
+// Example demonstrates middleware usage.
+func Example_middleware() {
+	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
+
+	s := scheduler.New(
+		scheduler.WithMiddleware(
+			scheduler.Recovery(func(jobName string, r interface{}) {
+				logger.Error("Job panicked", "job", jobName, "panic", r)
+			}),
+			scheduler.Logging(&slogAdapter{logger}),
+			scheduler.Timeout(5*time.Minute),
+		),
+	)
+
+	s.Register(&scheduler.Job{
+		Name:     "data-sync",
+		Schedule: "0 */2 * * *", // Every 2 hours
+		Handler: func(_ context.Context) error {
+			// Your sync logic here
+			return nil
+		},
+	})
+
+	s.Start()
+	defer s.Stop(context.Background())
+}
+
+// slogAdapter adapts slog.Logger to scheduler.Logger interface.
+type slogAdapter struct {
+	logger *slog.Logger
+}
+
+func (a *slogAdapter) Info(msg string, args ...interface{}) {
+	a.logger.Info(msg, args...)
+}
+
+func (a *slogAdapter) Error(msg string, args ...interface{}) {
+	a.logger.Error(msg, args...)
+}
+
+// Example demonstrates multiple jobs with different schedules.
+func Example_multipleJobs() {
+	s := scheduler.New()
+
+	// Cleanup old data every night at 2 AM
+	s.Register(&scheduler.Job{
+		Name:     "cleanup",
+		Schedule: "0 2 * * *",
+		Tags:     []string{"maintenance"},
+		Handler: func(_ context.Context) error {
+			fmt.Println("Cleaning up old data...")
+			return nil
+		},
+	})
+
+	// Health check every 5 minutes
+	s.Register(&scheduler.Job{
+		Name:     "health-check",
+		Schedule: "*/5 * * * *",
+		Tags:     []string{"monitoring"},
+		Handler: func(_ context.Context) error {
+			fmt.Println("Running health check...")
+			return nil
+		},
+	})
+
+	// Weekly backup on Sundays at 1 AM
+	s.Register(&scheduler.Job{
+		Name:     "weekly-backup",
+		Schedule: "0 1 * * 0",
+		Tags:     []string{"backup"},
+		Handler: func(_ context.Context) error {
+			fmt.Println("Creating weekly backup...")
+			return nil
+		},
+	})
+
+	s.Start()
+	defer s.Stop(context.Background())
+}
+
+// Example demonstrates graceful shutdown with timeout.
+func Example_gracefulShutdown() {
+	s := scheduler.New()
+
+	s.Register(&scheduler.Job{
+		Name:     "long-running",
+		Schedule: "* * * * *",
+		Handler: func(ctx context.Context) error {
+			select {
+			case <-time.After(30 * time.Second):
+				fmt.Println("Job completed")
+			case <-ctx.Done():
+				fmt.Println("Job canceled, cleaning up...")
+				return ctx.Err()
+			}
+			return nil
+		},
+	})
+
+	s.Start()
+
+	// Simulate shutdown signal
+	time.Sleep(5 * time.Second)
+
+	// Give jobs 10 seconds to finish
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	if err := s.Stop(shutdownCtx); err != nil {
+		fmt.Printf("Shutdown error: %v\n", err)
+	}
+}

plugin/scheduler/integration_test.go

@@ -0,0 +1,393 @@
+package scheduler_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/usememos/memos/plugin/scheduler"
+)
+
+// TestRealWorldScenario tests a realistic multi-job scenario.
+func TestRealWorldScenario(t *testing.T) {
+	var (
+		quickJobCount  atomic.Int32
+		hourlyJobCount atomic.Int32
+		logEntries     []string
+		logMu          sync.Mutex
+	)
+
+	logger := &testLogger{
+		onInfo: func(msg string, _ ...interface{}) {
+			logMu.Lock()
+			logEntries = append(logEntries, fmt.Sprintf("INFO: %s", msg))
+			logMu.Unlock()
+		},
+		onError: func(msg string, _ ...interface{}) {
+			logMu.Lock()
+			logEntries = append(logEntries, fmt.Sprintf("ERROR: %s", msg))
+			logMu.Unlock()
+		},
+	}
+
+	s := scheduler.New(
+		scheduler.WithTimezone("UTC"),
+		scheduler.WithMiddleware(
+			scheduler.Recovery(func(jobName string, r interface{}) {
+				t.Logf("Job %s panicked: %v", jobName, r)
+			}),
+			scheduler.Logging(logger),
+			scheduler.Timeout(5*time.Second),
+		),
+	)
+
+	// Quick job (every second)
+	s.Register(&scheduler.Job{
+		Name:     "quick-check",
+		Schedule: "* * * * * *",
+		Handler: func(_ context.Context) error {
+			quickJobCount.Add(1)
+			time.Sleep(100 * time.Millisecond)
+			return nil
+		},
+	})
+
+	// Slower job (every 2 seconds)
+	s.Register(&scheduler.Job{
+		Name:     "slow-process",
+		Schedule: "*/2 * * * * *",
+		Handler: func(_ context.Context) error {
+			hourlyJobCount.Add(1)
+			time.Sleep(500 * time.Millisecond)
+			return nil
+		},
+	})
+
+	// Start scheduler
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start scheduler: %v", err)
+	}
+
+	// Let it run for 5 seconds
+	time.Sleep(5 * time.Second)
+
+	// Graceful shutdown
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop scheduler: %v", err)
+	}
+
+	// Verify execution counts
+	quick := quickJobCount.Load()
+	slow := hourlyJobCount.Load()
+
+	t.Logf("Quick job ran %d times", quick)
+	t.Logf("Slow job ran %d times", slow)
+
+	if quick < 4 {
+		t.Errorf("expected quick job to run at least 4 times, ran %d", quick)
+	}
+
+	if slow < 2 {
+		t.Errorf("expected slow job to run at least 2 times, ran %d", slow)
+	}
+
+	// Verify logging
+	logMu.Lock()
+	defer logMu.Unlock()
+
+	hasStartLog := false
+	hasCompleteLog := false
+	for _, entry := range logEntries {
+		if contains(entry, "Job started") {
+			hasStartLog = true
+		}
+		if contains(entry, "Job completed") {
+			hasCompleteLog = true
+		}
+	}
+
+	if !hasStartLog {
+		t.Error("expected job start logs")
+	}
+	if !hasCompleteLog {
+		t.Error("expected job completion logs")
+	}
+}
+
+// TestCancellationDuringExecution verifies jobs can be canceled mid-execution.
+func TestCancellationDuringExecution(t *testing.T) {
+	var canceled atomic.Bool
+	var started atomic.Bool
+
+	s := scheduler.New()
+
+	s.Register(&scheduler.Job{
+		Name:     "long-job",
+		Schedule: "* * * * * *",
+		Handler: func(ctx context.Context) error {
+			started.Store(true)
+			// Simulate long-running work
+			for i := 0; i < 100; i++ {
+				select {
+				case <-ctx.Done():
+					canceled.Store(true)
+					return ctx.Err()
+				case <-time.After(100 * time.Millisecond):
+					// Keep working
+				}
+			}
+			return nil
+		},
+	})
+
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start: %v", err)
+	}
+
+	// Wait until job starts
+	for i := 0; i < 30; i++ {
+		if started.Load() {
+			break
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	if !started.Load() {
+		t.Fatal("job did not start within timeout")
+	}
+
+	// Stop with reasonable timeout
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Logf("stop returned error (may be expected): %v", err)
+	}
+
+	if !canceled.Load() {
+		t.Error("expected job to detect cancellation")
+	}
+}
+
+// TestTimezoneHandling verifies timezone-aware scheduling.
+func TestTimezoneHandling(t *testing.T) {
+	// Parse a schedule in a specific timezone
+	schedule, err := scheduler.ParseCronExpression("0 9 * * *") // 9 AM
+	if err != nil {
+		t.Fatalf("failed to parse schedule: %v", err)
+	}
+
+	// Test in New York timezone
+	nyc, err := time.LoadLocation("America/New_York")
+	if err != nil {
+		t.Fatalf("failed to load timezone: %v", err)
+	}
+
+	// Current time: 8:30 AM in New York
+	now := time.Date(2025, 1, 15, 8, 30, 0, 0, nyc)
+
+	// Next run should be 9:00 AM same day
+	next := schedule.Next(now)
+	expected := time.Date(2025, 1, 15, 9, 0, 0, 0, nyc)
+
+	if !next.Equal(expected) {
+		t.Errorf("next = %v, expected %v", next, expected)
+	}
+
+	// If it's already past 9 AM
+	now = time.Date(2025, 1, 15, 9, 30, 0, 0, nyc)
+	next = schedule.Next(now)
+	expected = time.Date(2025, 1, 16, 9, 0, 0, 0, nyc)
+
+	if !next.Equal(expected) {
+		t.Errorf("next = %v, expected %v", next, expected)
+	}
+}
+
+// TestErrorPropagation verifies error handling.
+func TestErrorPropagation(t *testing.T) {
+	var errorLogged atomic.Bool
+
+	logger := &testLogger{
+		onError: func(msg string, _ ...interface{}) {
+			if msg == "Job failed" {
+				errorLogged.Store(true)
+			}
+		},
+	}
+
+	s := scheduler.New(
+		scheduler.WithMiddleware(
+			scheduler.Logging(logger),
+		),
+	)
+
+	s.Register(&scheduler.Job{
+		Name:     "failing-job",
+		Schedule: "* * * * * *",
+		Handler: func(_ context.Context) error {
+			return errors.New("intentional error")
+		},
+	})
+
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start: %v", err)
+	}
+
+	// Let it run once
+	time.Sleep(1500 * time.Millisecond)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop: %v", err)
+	}
+
+	if !errorLogged.Load() {
+		t.Error("expected error to be logged")
+	}
+}
+
+// TestPanicRecovery verifies panic recovery middleware.
+func TestPanicRecovery(t *testing.T) {
+	var panicRecovered atomic.Bool
+
+	s := scheduler.New(
+		scheduler.WithMiddleware(
+			scheduler.Recovery(func(jobName string, r interface{}) {
+				panicRecovered.Store(true)
+				t.Logf("Recovered from panic in job %s: %v", jobName, r)
+			}),
+		),
+	)
+
+	s.Register(&scheduler.Job{
+		Name:     "panicking-job",
+		Schedule: "* * * * * *",
+		Handler: func(_ context.Context) error {
+			panic("intentional panic for testing")
+		},
+	})
+
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start: %v", err)
+	}
+
+	// Let it run once
+	time.Sleep(1500 * time.Millisecond)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop: %v", err)
+	}
+
+	if !panicRecovered.Load() {
+		t.Error("expected panic to be recovered")
+	}
+}
+
+// TestMultipleJobsWithDifferentSchedules verifies concurrent job execution.
+func TestMultipleJobsWithDifferentSchedules(t *testing.T) {
+	var (
+		job1Count atomic.Int32
+		job2Count atomic.Int32
+		job3Count atomic.Int32
+	)
+
+	s := scheduler.New()
+
+	// Job 1: Every second
+	s.Register(&scheduler.Job{
+		Name:     "job-1sec",
+		Schedule: "* * * * * *",
+		Handler: func(_ context.Context) error {
+			job1Count.Add(1)
+			return nil
+		},
+	})
+
+	// Job 2: Every 2 seconds
+	s.Register(&scheduler.Job{
+		Name:     "job-2sec",
+		Schedule: "*/2 * * * * *",
+		Handler: func(_ context.Context) error {
+			job2Count.Add(1)
+			return nil
+		},
+	})
+
+	// Job 3: Every 3 seconds
+	s.Register(&scheduler.Job{
+		Name:     "job-3sec",
+		Schedule: "*/3 * * * * *",
+		Handler: func(_ context.Context) error {
+			job3Count.Add(1)
+			return nil
+		},
+	})
+
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start: %v", err)
+	}
+
+	// Let them run for 6 seconds
+	time.Sleep(6 * time.Second)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop: %v", err)
+	}
+
+	// Verify counts (allowing for timing variance)
+	c1 := job1Count.Load()
+	c2 := job2Count.Load()
+	c3 := job3Count.Load()
+
+	t.Logf("Job 1 ran %d times, Job 2 ran %d times, Job 3 ran %d times", c1, c2, c3)
+
+	if c1 < 5 {
+		t.Errorf("expected job1 to run at least 5 times, ran %d", c1)
+	}
+	if c2 < 2 {
+		t.Errorf("expected job2 to run at least 2 times, ran %d", c2)
+	}
+	if c3 < 1 {
+		t.Errorf("expected job3 to run at least 1 time, ran %d", c3)
+	}
+}
+
+// Helpers
+
+type testLogger struct {
+	onInfo  func(msg string, args ...interface{})
+	onError func(msg string, args ...interface{})
+}
+
+func (l *testLogger) Info(msg string, args ...interface{}) {
+	if l.onInfo != nil {
+		l.onInfo(msg, args...)
+	}
+}
+
+func (l *testLogger) Error(msg string, args ...interface{}) {
+	if l.onError != nil {
+		l.onError(msg, args...)
+	}
+}
+
+func contains(s, substr string) bool {
+	return strings.Contains(s, substr)
+}

plugin/scheduler/job.go

@@ -0,0 +1,58 @@
+package scheduler
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+)
+
+// JobHandler is the function signature for scheduled job handlers.
+// The context passed to the handler will be canceled if the scheduler is shutting down.
+type JobHandler func(ctx context.Context) error
+
+// Job represents a scheduled task.
+type Job struct {
+	// Name is a unique identifier for this job (required).
+	// Used for logging and metrics.
+	Name string
+
+	// Schedule is a cron expression defining when this job runs (required).
+	// Supports standard 5-field format: "minute hour day month weekday"
+	// Examples: "0 * * * *" (hourly), "0 0 * * *" (daily at midnight)
+	Schedule string
+
+	// Timezone for schedule evaluation (optional, defaults to UTC).
+	// Use IANA timezone names: "America/New_York", "Europe/London", etc.
+	Timezone string
+
+	// Handler is the function to execute when the job triggers (required).
+	Handler JobHandler
+
+	// Description provides human-readable context about what this job does (optional).
+	Description string
+
+	// Tags allow categorizing jobs for filtering/monitoring (optional).
+	Tags []string
+}
+
+// Validate checks if the job definition is valid.
+func (j *Job) Validate() error {
+	if j.Name == "" {
+		return errors.New("job name is required")
+	}
+
+	if j.Schedule == "" {
+		return errors.New("job schedule is required")
+	}
+
+	// Validate cron expression using parser
+	if _, err := ParseCronExpression(j.Schedule); err != nil {
+		return errors.Wrap(err, "invalid cron expression")
+	}
+
+	if j.Handler == nil {
+		return errors.New("job handler is required")
+	}
+
+	return nil
+}

plugin/scheduler/job_test.go

@@ -0,0 +1,90 @@
+package scheduler
+
+import (
+	"context"
+	"testing"
+)
+
+func TestJobDefinition(t *testing.T) {
+	callCount := 0
+	job := &Job{
+		Name: "test-job",
+		Handler: func(_ context.Context) error {
+			callCount++
+			return nil
+		},
+	}
+
+	if job.Name != "test-job" {
+		t.Errorf("expected name 'test-job', got %s", job.Name)
+	}
+
+	// Test handler execution
+	if err := job.Handler(context.Background()); err != nil {
+		t.Fatalf("handler failed: %v", err)
+	}
+
+	if callCount != 1 {
+		t.Errorf("expected handler to be called once, called %d times", callCount)
+	}
+}
+
+func TestJobValidation(t *testing.T) {
+	tests := []struct {
+		name    string
+		job     *Job
+		wantErr bool
+	}{
+		{
+			name: "valid job",
+			job: &Job{
+				Name:     "valid",
+				Schedule: "0 * * * *",
+				Handler:  func(_ context.Context) error { return nil },
+			},
+			wantErr: false,
+		},
+		{
+			name: "missing name",
+			job: &Job{
+				Schedule: "0 * * * *",
+				Handler:  func(_ context.Context) error { return nil },
+			},
+			wantErr: true,
+		},
+		{
+			name: "missing schedule",
+			job: &Job{
+				Name:    "test",
+				Handler: func(_ context.Context) error { return nil },
+			},
+			wantErr: true,
+		},
+		{
+			name: "invalid cron expression",
+			job: &Job{
+				Name:     "test",
+				Schedule: "invalid cron",
+				Handler:  func(_ context.Context) error { return nil },
+			},
+			wantErr: true,
+		},
+		{
+			name: "missing handler",
+			job: &Job{
+				Name:     "test",
+				Schedule: "0 * * * *",
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.job.Validate()
+			if (err != nil) != tt.wantErr {
+				t.Errorf("Validate() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}

plugin/scheduler/middleware.go

@@ -0,0 +1,120 @@
+package scheduler
+
+import (
+	"context"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// Middleware wraps a JobHandler to add cross-cutting behavior.
+type Middleware func(JobHandler) JobHandler
+
+// Chain combines multiple middleware into a single middleware.
+// Middleware are applied in the order they're provided (left to right).
+func Chain(middlewares ...Middleware) Middleware {
+	return func(handler JobHandler) JobHandler {
+		// Apply middleware in reverse order so first middleware wraps outermost
+		for i := len(middlewares) - 1; i >= 0; i-- {
+			handler = middlewares[i](handler)
+		}
+		return handler
+	}
+}
+
+// Recovery recovers from panics in job handlers and converts them to errors.
+func Recovery(onPanic func(jobName string, recovered interface{})) Middleware {
+	return func(next JobHandler) JobHandler {
+		return func(ctx context.Context) (err error) {
+			defer func() {
+				if r := recover(); r != nil {
+					jobName := getJobName(ctx)
+					if onPanic != nil {
+						onPanic(jobName, r)
+					}
+					err = errors.Errorf("job %q panicked: %v", jobName, r)
+				}
+			}()
+			return next(ctx)
+		}
+	}
+}
+
+// Logger is a minimal logging interface.
+type Logger interface {
+	Info(msg string, args ...interface{})
+	Error(msg string, args ...interface{})
+}
+
+// Logging adds execution logging to jobs.
+func Logging(logger Logger) Middleware {
+	return func(next JobHandler) JobHandler {
+		return func(ctx context.Context) error {
+			jobName := getJobName(ctx)
+			start := time.Now()
+
+			logger.Info("Job started", "job", jobName)
+
+			err := next(ctx)
+			duration := time.Since(start)
+
+			if err != nil {
+				logger.Error("Job failed", "job", jobName, "duration", duration, "error", err)
+			} else {
+				logger.Info("Job completed", "job", jobName, "duration", duration)
+			}
+
+			return err
+		}
+	}
+}
+
+// Timeout wraps a job handler with a timeout.
+func Timeout(duration time.Duration) Middleware {
+	return func(next JobHandler) JobHandler {
+		return func(ctx context.Context) error {
+			ctx, cancel := context.WithTimeout(ctx, duration)
+			defer cancel()
+
+			done := make(chan error, 1)
+			go func() {
+				done <- next(ctx)
+			}()
+
+			select {
+			case err := <-done:
+				return err
+			case <-ctx.Done():
+				return errors.Errorf("job %q timed out after %v", getJobName(ctx), duration)
+			}
+		}
+	}
+}
+
+// Context keys for job metadata.
+type contextKey int
+
+const (
+	jobNameKey contextKey = iota
+)
+
+// withJobName adds the job name to the context.
+func withJobName(ctx context.Context, name string) context.Context {
+	return context.WithValue(ctx, jobNameKey, name)
+}
+
+// getJobName retrieves the job name from the context.
+func getJobName(ctx context.Context) string {
+	if name, ok := ctx.Value(jobNameKey).(string); ok {
+		return name
+	}
+	return "unknown"
+}
+
+// GetJobName retrieves the job name from the context (public API).
+// Returns empty string if not found.
+//
+//nolint:revive // GetJobName is the public API, getJobName is internal
+func GetJobName(ctx context.Context) string {
+	return getJobName(ctx)
+}

plugin/scheduler/middleware_test.go

@@ -0,0 +1,146 @@
+package scheduler
+
+import (
+	"context"
+	"errors"
+	"sync/atomic"
+	"testing"
+)
+
+func TestMiddlewareChaining(t *testing.T) {
+	var order []string
+
+	mw1 := func(next JobHandler) JobHandler {
+		return func(ctx context.Context) error {
+			order = append(order, "before-1")
+			err := next(ctx)
+			order = append(order, "after-1")
+			return err
+		}
+	}
+
+	mw2 := func(next JobHandler) JobHandler {
+		return func(ctx context.Context) error {
+			order = append(order, "before-2")
+			err := next(ctx)
+			order = append(order, "after-2")
+			return err
+		}
+	}
+
+	handler := func(_ context.Context) error {
+		order = append(order, "handler")
+		return nil
+	}
+
+	chain := Chain(mw1, mw2)
+	wrapped := chain(handler)
+
+	if err := wrapped(context.Background()); err != nil {
+		t.Fatalf("wrapped handler failed: %v", err)
+	}
+
+	expected := []string{"before-1", "before-2", "handler", "after-2", "after-1"}
+	if len(order) != len(expected) {
+		t.Fatalf("expected %d calls, got %d", len(expected), len(order))
+	}
+
+	for i, want := range expected {
+		if order[i] != want {
+			t.Errorf("order[%d] = %q, want %q", i, order[i], want)
+		}
+	}
+}
+
+func TestRecoveryMiddleware(t *testing.T) {
+	var panicRecovered atomic.Bool
+
+	onPanic := func(_ string, _ interface{}) {
+		panicRecovered.Store(true)
+	}
+
+	handler := func(_ context.Context) error {
+		panic("simulated panic")
+	}
+
+	recovery := Recovery(onPanic)
+	wrapped := recovery(handler)
+
+	// Should not panic, error should be returned
+	err := wrapped(withJobName(context.Background(), "test-job"))
+	if err == nil {
+		t.Error("expected error from recovered panic")
+	}
+
+	if !panicRecovered.Load() {
+		t.Error("panic handler was not called")
+	}
+}
+
+func TestLoggingMiddleware(t *testing.T) {
+	var loggedStart, loggedEnd atomic.Bool
+	var loggedError atomic.Bool
+
+	logger := &testLogger{
+		onInfo: func(msg string, _ ...interface{}) {
+			if msg == "Job started" {
+				loggedStart.Store(true)
+			} else if msg == "Job completed" {
+				loggedEnd.Store(true)
+			}
+		},
+		onError: func(msg string, _ ...interface{}) {
+			if msg == "Job failed" {
+				loggedError.Store(true)
+			}
+		},
+	}
+
+	// Test successful execution
+	handler := func(_ context.Context) error {
+		return nil
+	}
+
+	logging := Logging(logger)
+	wrapped := logging(handler)
+
+	if err := wrapped(withJobName(context.Background(), "test-job")); err != nil {
+		t.Fatalf("handler failed: %v", err)
+	}
+
+	if !loggedStart.Load() {
+		t.Error("start was not logged")
+	}
+	if !loggedEnd.Load() {
+		t.Error("end was not logged")
+	}
+
+	// Test error handling
+	handlerErr := func(_ context.Context) error {
+		return errors.New("job error")
+	}
+
+	wrappedErr := logging(handlerErr)
+	_ = wrappedErr(withJobName(context.Background(), "test-job-error"))
+
+	if !loggedError.Load() {
+		t.Error("error was not logged")
+	}
+}
+
+type testLogger struct {
+	onInfo  func(msg string, args ...interface{})
+	onError func(msg string, args ...interface{})
+}
+
+func (l *testLogger) Info(msg string, args ...interface{}) {
+	if l.onInfo != nil {
+		l.onInfo(msg, args...)
+	}
+}
+
+func (l *testLogger) Error(msg string, args ...interface{}) {
+	if l.onError != nil {
+		l.onError(msg, args...)
+	}
+}

plugin/scheduler/parser.go

@@ -0,0 +1,229 @@
+package scheduler
+
+import (
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// Schedule represents a parsed cron expression.
+type Schedule struct {
+	seconds  fieldMatcher // 0-59 (optional, for 6-field format)
+	minutes  fieldMatcher // 0-59
+	hours    fieldMatcher // 0-23
+	days     fieldMatcher // 1-31
+	months   fieldMatcher // 1-12
+	weekdays fieldMatcher // 0-7 (0 and 7 are Sunday)
+	hasSecs  bool
+}
+
+// fieldMatcher determines if a field value matches.
+type fieldMatcher interface {
+	matches(value int) bool
+}
+
+// ParseCronExpression parses a cron expression and returns a Schedule.
+// Supports both 5-field (minute hour day month weekday) and 6-field (second minute hour day month weekday) formats.
+func ParseCronExpression(expr string) (*Schedule, error) {
+	if expr == "" {
+		return nil, errors.New("empty cron expression")
+	}
+
+	fields := strings.Fields(expr)
+	if len(fields) != 5 && len(fields) != 6 {
+		return nil, errors.Errorf("invalid cron expression: expected 5 or 6 fields, got %d", len(fields))
+	}
+
+	s := &Schedule{
+		hasSecs: len(fields) == 6,
+	}
+
+	var err error
+	offset := 0
+
+	// Parse seconds (if 6-field format)
+	if s.hasSecs {
+		s.seconds, err = parseField(fields[0], 0, 59)
+		if err != nil {
+			return nil, errors.Wrap(err, "invalid seconds field")
+		}
+		offset = 1
+	} else {
+		s.seconds = &exactMatcher{value: 0} // Default to 0 seconds
+	}
+
+	// Parse minutes
+	s.minutes, err = parseField(fields[offset], 0, 59)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid minutes field")
+	}
+
+	// Parse hours
+	s.hours, err = parseField(fields[offset+1], 0, 23)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid hours field")
+	}
+
+	// Parse days
+	s.days, err = parseField(fields[offset+2], 1, 31)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid days field")
+	}
+
+	// Parse months
+	s.months, err = parseField(fields[offset+3], 1, 12)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid months field")
+	}
+
+	// Parse weekdays (0-7, where both 0 and 7 represent Sunday)
+	s.weekdays, err = parseField(fields[offset+4], 0, 7)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid weekdays field")
+	}
+
+	return s, nil
+}
+
+// Next returns the next time the schedule should run after the given time.
+func (s *Schedule) Next(from time.Time) time.Time {
+	// Start from the next second/minute
+	if s.hasSecs {
+		from = from.Add(1 * time.Second).Truncate(time.Second)
+	} else {
+		from = from.Add(1 * time.Minute).Truncate(time.Minute)
+	}
+
+	// Cap search at 4 years to prevent infinite loops
+	maxTime := from.AddDate(4, 0, 0)
+
+	for from.Before(maxTime) {
+		if s.matches(from) {
+			return from
+		}
+
+		// Advance to next potential match
+		if s.hasSecs {
+			from = from.Add(1 * time.Second)
+		} else {
+			from = from.Add(1 * time.Minute)
+		}
+	}
+
+	// Should never reach here with valid cron expressions
+	return time.Time{}
+}
+
+// matches checks if the given time matches the schedule.
+func (s *Schedule) matches(t time.Time) bool {
+	return s.seconds.matches(t.Second()) &&
+		s.minutes.matches(t.Minute()) &&
+		s.hours.matches(t.Hour()) &&
+		s.months.matches(int(t.Month())) &&
+		(s.days.matches(t.Day()) || s.weekdays.matches(int(t.Weekday())))
+}
+
+// parseField parses a single cron field (supports *, ranges, lists, steps).
+func parseField(field string, min, max int) (fieldMatcher, error) {
+	// Wildcard
+	if field == "*" {
+		return &wildcardMatcher{}, nil
+	}
+
+	// Step values (*/N)
+	if strings.HasPrefix(field, "*/") {
+		step, err := strconv.Atoi(field[2:])
+		if err != nil || step < 1 || step > max {
+			return nil, errors.Errorf("invalid step value: %s", field)
+		}
+		return &stepMatcher{step: step, min: min, max: max}, nil
+	}
+
+	// List (1,2,3)
+	if strings.Contains(field, ",") {
+		parts := strings.Split(field, ",")
+		values := make([]int, 0, len(parts))
+		for _, p := range parts {
+			val, err := strconv.Atoi(strings.TrimSpace(p))
+			if err != nil || val < min || val > max {
+				return nil, errors.Errorf("invalid list value: %s", p)
+			}
+			values = append(values, val)
+		}
+		return &listMatcher{values: values}, nil
+	}
+
+	// Range (1-5)
+	if strings.Contains(field, "-") {
+		parts := strings.Split(field, "-")
+		if len(parts) != 2 {
+			return nil, errors.Errorf("invalid range: %s", field)
+		}
+		start, err1 := strconv.Atoi(strings.TrimSpace(parts[0]))
+		end, err2 := strconv.Atoi(strings.TrimSpace(parts[1]))
+		if err1 != nil || err2 != nil || start < min || end > max || start > end {
+			return nil, errors.Errorf("invalid range: %s", field)
+		}
+		return &rangeMatcher{start: start, end: end}, nil
+	}
+
+	// Exact value
+	val, err := strconv.Atoi(field)
+	if err != nil || val < min || val > max {
+		return nil, errors.Errorf("invalid value: %s (must be between %d and %d)", field, min, max)
+	}
+	return &exactMatcher{value: val}, nil
+}
+
+// wildcardMatcher matches any value.
+type wildcardMatcher struct{}
+
+func (*wildcardMatcher) matches(_ int) bool {
+	return true
+}
+
+// exactMatcher matches a specific value.
+type exactMatcher struct {
+	value int
+}
+
+func (m *exactMatcher) matches(value int) bool {
+	return value == m.value
+}
+
+// rangeMatcher matches values in a range.
+type rangeMatcher struct {
+	start, end int
+}
+
+func (m *rangeMatcher) matches(value int) bool {
+	return value >= m.start && value <= m.end
+}
+
+// listMatcher matches any value in a list.
+type listMatcher struct {
+	values []int
+}
+
+func (m *listMatcher) matches(value int) bool {
+	for _, v := range m.values {
+		if v == value {
+			return true
+		}
+	}
+	return false
+}
+
+// stepMatcher matches values at regular intervals.
+type stepMatcher struct {
+	step, min, max int
+}
+
+func (m *stepMatcher) matches(value int) bool {
+	if value < m.min || value > m.max {
+		return false
+	}
+	return (value-m.min)%m.step == 0
+}

plugin/scheduler/parser_test.go

@@ -0,0 +1,127 @@
+package scheduler
+
+import (
+	"testing"
+	"time"
+)
+
+func TestParseCronExpression(t *testing.T) {
+	tests := []struct {
+		name    string
+		expr    string
+		wantErr bool
+	}{
+		// Standard 5-field format
+		{"every minute", "* * * * *", false},
+		{"hourly", "0 * * * *", false},
+		{"daily midnight", "0 0 * * *", false},
+		{"weekly sunday", "0 0 * * 0", false},
+		{"monthly", "0 0 1 * *", false},
+		{"specific time", "30 14 * * *", false}, // 2:30 PM daily
+		{"range", "0 9-17 * * *", false},        // Every hour 9 AM - 5 PM
+		{"step", "*/15 * * * *", false},         // Every 15 minutes
+		{"list", "0 8,12,18 * * *", false},      // 8 AM, 12 PM, 6 PM
+
+		// 6-field format with seconds
+		{"with seconds", "0 * * * * *", false},
+		{"every 30 seconds", "*/30 * * * * *", false},
+
+		// Invalid expressions
+		{"empty", "", true},
+		{"too few fields", "* * *", true},
+		{"too many fields", "* * * * * * *", true},
+		{"invalid minute", "60 * * * *", true},
+		{"invalid hour", "0 24 * * *", true},
+		{"invalid day", "0 0 32 * *", true},
+		{"invalid month", "0 0 1 13 *", true},
+		{"invalid weekday", "0 0 * * 8", true},
+		{"garbage", "not a cron expression", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			schedule, err := ParseCronExpression(tt.expr)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseCronExpression(%q) error = %v, wantErr %v", tt.expr, err, tt.wantErr)
+				return
+			}
+			if !tt.wantErr && schedule == nil {
+				t.Errorf("ParseCronExpression(%q) returned nil schedule without error", tt.expr)
+			}
+		})
+	}
+}
+
+func TestScheduleNext(t *testing.T) {
+	tests := []struct {
+		name     string
+		expr     string
+		from     time.Time
+		expected time.Time
+	}{
+		{
+			name:     "every minute from start of hour",
+			expr:     "* * * * *",
+			from:     time.Date(2025, 1, 1, 10, 0, 0, 0, time.UTC),
+			expected: time.Date(2025, 1, 1, 10, 1, 0, 0, time.UTC),
+		},
+		{
+			name:     "hourly at minute 30",
+			expr:     "30 * * * *",
+			from:     time.Date(2025, 1, 1, 10, 0, 0, 0, time.UTC),
+			expected: time.Date(2025, 1, 1, 10, 30, 0, 0, time.UTC),
+		},
+		{
+			name:     "hourly at minute 30 (already past)",
+			expr:     "30 * * * *",
+			from:     time.Date(2025, 1, 1, 10, 45, 0, 0, time.UTC),
+			expected: time.Date(2025, 1, 1, 11, 30, 0, 0, time.UTC),
+		},
+		{
+			name:     "daily at 2 AM",
+			expr:     "0 2 * * *",
+			from:     time.Date(2025, 1, 1, 10, 0, 0, 0, time.UTC),
+			expected: time.Date(2025, 1, 2, 2, 0, 0, 0, time.UTC),
+		},
+		{
+			name:     "every 15 minutes",
+			expr:     "*/15 * * * *",
+			from:     time.Date(2025, 1, 1, 10, 7, 0, 0, time.UTC),
+			expected: time.Date(2025, 1, 1, 10, 15, 0, 0, time.UTC),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			schedule, err := ParseCronExpression(tt.expr)
+			if err != nil {
+				t.Fatalf("failed to parse expression: %v", err)
+			}
+
+			next := schedule.Next(tt.from)
+			if !next.Equal(tt.expected) {
+				t.Errorf("Next(%v) = %v, expected %v", tt.from, next, tt.expected)
+			}
+		})
+	}
+}
+
+func TestScheduleNextWithTimezone(t *testing.T) {
+	nyc, _ := time.LoadLocation("America/New_York")
+
+	// Schedule for 9 AM in New York
+	schedule, err := ParseCronExpression("0 9 * * *")
+	if err != nil {
+		t.Fatalf("failed to parse expression: %v", err)
+	}
+
+	// Current time: 8 AM in New York
+	from := time.Date(2025, 1, 1, 8, 0, 0, 0, nyc)
+	next := schedule.Next(from)
+
+	// Should be 9 AM same day in New York
+	expected := time.Date(2025, 1, 1, 9, 0, 0, 0, nyc)
+	if !next.Equal(expected) {
+		t.Errorf("Next(%v) = %v, expected %v", from, next, expected)
+	}
+}

plugin/scheduler/scheduler.go

@@ -0,0 +1,202 @@
+package scheduler
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+// Scheduler manages scheduled jobs.
+type Scheduler struct {
+	jobs       map[string]*registeredJob
+	jobsMu     sync.RWMutex
+	timezone   *time.Location
+	middleware Middleware
+	running    bool
+	runningMu  sync.RWMutex
+	stopCh     chan struct{}
+	wg         sync.WaitGroup
+}
+
+// registeredJob wraps a Job with runtime state.
+type registeredJob struct {
+	job      *Job
+	cancelFn context.CancelFunc
+}
+
+// Option configures a Scheduler.
+type Option func(*Scheduler)
+
+// WithTimezone sets the default timezone for all jobs.
+func WithTimezone(tz string) Option {
+	return func(s *Scheduler) {
+		loc, err := time.LoadLocation(tz)
+		if err != nil {
+			// Default to UTC on invalid timezone
+			loc = time.UTC
+		}
+		s.timezone = loc
+	}
+}
+
+// WithMiddleware sets middleware to wrap all job handlers.
+func WithMiddleware(mw ...Middleware) Option {
+	return func(s *Scheduler) {
+		if len(mw) > 0 {
+			s.middleware = Chain(mw...)
+		}
+	}
+}
+
+// New creates a new Scheduler with optional configuration.
+func New(opts ...Option) *Scheduler {
+	s := &Scheduler{
+		jobs:     make(map[string]*registeredJob),
+		timezone: time.UTC,
+		stopCh:   make(chan struct{}),
+	}
+
+	for _, opt := range opts {
+		opt(s)
+	}
+
+	return s
+}
+
+// Register adds a job to the scheduler.
+// Jobs must be registered before calling Start().
+func (s *Scheduler) Register(job *Job) error {
+	if job == nil {
+		return errors.New("job cannot be nil")
+	}
+
+	if err := job.Validate(); err != nil {
+		return errors.Wrap(err, "invalid job")
+	}
+
+	s.jobsMu.Lock()
+	defer s.jobsMu.Unlock()
+
+	if _, exists := s.jobs[job.Name]; exists {
+		return errors.Errorf("job with name %q already registered", job.Name)
+	}
+
+	s.jobs[job.Name] = &registeredJob{job: job}
+	return nil
+}
+
+// Start begins executing scheduled jobs.
+func (s *Scheduler) Start() error {
+	s.runningMu.Lock()
+	defer s.runningMu.Unlock()
+
+	if s.running {
+		return errors.New("scheduler already running")
+	}
+
+	s.jobsMu.RLock()
+	defer s.jobsMu.RUnlock()
+
+	// Parse and schedule all jobs
+	for _, rj := range s.jobs {
+		schedule, err := ParseCronExpression(rj.job.Schedule)
+		if err != nil {
+			return errors.Wrapf(err, "failed to parse schedule for job %q", rj.job.Name)
+		}
+
+		ctx, cancel := context.WithCancel(context.Background())
+		rj.cancelFn = cancel
+
+		s.wg.Add(1)
+		go s.runJobWithSchedule(ctx, rj, schedule)
+	}
+
+	s.running = true
+	return nil
+}
+
+// runJobWithSchedule executes a job according to its cron schedule.
+func (s *Scheduler) runJobWithSchedule(ctx context.Context, rj *registeredJob, schedule *Schedule) {
+	defer s.wg.Done()
+
+	// Apply middleware to handler
+	handler := rj.job.Handler
+	if s.middleware != nil {
+		handler = s.middleware(handler)
+	}
+
+	for {
+		// Calculate next run time
+		now := time.Now()
+		if rj.job.Timezone != "" {
+			loc, err := time.LoadLocation(rj.job.Timezone)
+			if err == nil {
+				now = now.In(loc)
+			}
+		} else if s.timezone != nil {
+			now = now.In(s.timezone)
+		}
+
+		next := schedule.Next(now)
+		duration := time.Until(next)
+
+		timer := time.NewTimer(duration)
+
+		select {
+		case <-timer.C:
+			// Add job name to context and execute
+			jobCtx := withJobName(ctx, rj.job.Name)
+			if err := handler(jobCtx); err != nil {
+				// Error already handled by middleware (if any)
+				_ = err
+			}
+		case <-ctx.Done():
+			// Stop the timer to prevent it from firing. The timer will be garbage collected.
+			timer.Stop()
+			return
+		case <-s.stopCh:
+			// Stop the timer to prevent it from firing. The timer will be garbage collected.
+			timer.Stop()
+			return
+		}
+	}
+}
+
+// Stop gracefully shuts down the scheduler.
+// It waits for all running jobs to complete or until the context is canceled.
+func (s *Scheduler) Stop(ctx context.Context) error {
+	s.runningMu.Lock()
+	if !s.running {
+		s.runningMu.Unlock()
+		return errors.New("scheduler not running")
+	}
+	s.running = false
+	s.runningMu.Unlock()
+
+	// Cancel all job contexts
+	s.jobsMu.RLock()
+	for _, rj := range s.jobs {
+		if rj.cancelFn != nil {
+			rj.cancelFn()
+		}
+	}
+	s.jobsMu.RUnlock()
+
+	// Signal stop and wait for jobs to finish
+	close(s.stopCh)
+
+	done := make(chan struct{})
+	go func() {
+		s.wg.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}

plugin/scheduler/scheduler_test.go

@@ -0,0 +1,165 @@
+package scheduler
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestSchedulerCreation(t *testing.T) {
+	s := New()
+	if s == nil {
+		t.Fatal("New() returned nil")
+	}
+}
+
+func TestSchedulerWithTimezone(t *testing.T) {
+	s := New(WithTimezone("America/New_York"))
+	if s == nil {
+		t.Fatal("New() with timezone returned nil")
+	}
+}
+
+func TestJobRegistration(t *testing.T) {
+	s := New()
+
+	job := &Job{
+		Name:     "test-registration",
+		Schedule: "0 * * * *",
+		Handler:  func(_ context.Context) error { return nil },
+	}
+
+	if err := s.Register(job); err != nil {
+		t.Fatalf("failed to register valid job: %v", err)
+	}
+
+	// Registering duplicate name should fail
+	if err := s.Register(job); err == nil {
+		t.Error("expected error when registering duplicate job name")
+	}
+}
+
+func TestSchedulerStartStop(t *testing.T) {
+	s := New()
+
+	var runCount atomic.Int32
+	job := &Job{
+		Name:     "test-start-stop",
+		Schedule: "* * * * * *", // Every second (6-field format)
+		Handler: func(_ context.Context) error {
+			runCount.Add(1)
+			return nil
+		},
+	}
+
+	if err := s.Register(job); err != nil {
+		t.Fatalf("failed to register job: %v", err)
+	}
+
+	// Start scheduler
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start scheduler: %v", err)
+	}
+
+	// Let it run for 2.5 seconds
+	time.Sleep(2500 * time.Millisecond)
+
+	// Stop scheduler
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop scheduler: %v", err)
+	}
+
+	count := runCount.Load()
+	// Should have run at least twice (at 0s and 1s, maybe 2s)
+	if count < 2 {
+		t.Errorf("expected job to run at least 2 times, ran %d times", count)
+	}
+
+	// Verify it stopped (count shouldn't increase)
+	finalCount := count
+	time.Sleep(1500 * time.Millisecond)
+	if runCount.Load() != finalCount {
+		t.Error("scheduler did not stop - job continued running")
+	}
+}
+
+func TestSchedulerWithMiddleware(t *testing.T) {
+	var executionLog []string
+	var logMu sync.Mutex
+
+	logger := &testLogger{
+		onInfo: func(msg string, _ ...interface{}) {
+			logMu.Lock()
+			executionLog = append(executionLog, fmt.Sprintf("INFO: %s", msg))
+			logMu.Unlock()
+		},
+		onError: func(msg string, _ ...interface{}) {
+			logMu.Lock()
+			executionLog = append(executionLog, fmt.Sprintf("ERROR: %s", msg))
+			logMu.Unlock()
+		},
+	}
+
+	s := New(WithMiddleware(
+		Recovery(func(jobName string, r interface{}) {
+			logMu.Lock()
+			executionLog = append(executionLog, fmt.Sprintf("PANIC: %s - %v", jobName, r))
+			logMu.Unlock()
+		}),
+		Logging(logger),
+	))
+
+	job := &Job{
+		Name:     "test-middleware",
+		Schedule: "* * * * * *", // Every second
+		Handler: func(_ context.Context) error {
+			return nil
+		},
+	}
+
+	if err := s.Register(job); err != nil {
+		t.Fatalf("failed to register job: %v", err)
+	}
+
+	if err := s.Start(); err != nil {
+		t.Fatalf("failed to start: %v", err)
+	}
+
+	time.Sleep(1500 * time.Millisecond)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := s.Stop(ctx); err != nil {
+		t.Fatalf("failed to stop: %v", err)
+	}
+
+	logMu.Lock()
+	defer logMu.Unlock()
+
+	// Should have at least one start and one completion log
+	hasStart := false
+	hasCompletion := false
+	for _, log := range executionLog {
+		if strings.Contains(log, "Job started") {
+			hasStart = true
+		}
+		if strings.Contains(log, "Job completed") {
+			hasCompletion = true
+		}
+	}
+
+	if !hasStart {
+		t.Error("expected job start log")
+	}
+	if !hasCompletion {
+		t.Error("expected job completion log")
+	}
+}

plugin/storage/s3/s3.go

@@ -0,0 +1,118 @@
+package s3
+
+import (
+	"context"
+	"io"
+	"time"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/config"
+	"github.com/aws/aws-sdk-go-v2/credentials"
+	"github.com/aws/aws-sdk-go-v2/feature/s3/manager"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/pkg/errors"
+
+	storepb "github.com/usememos/memos/proto/gen/store"
+)
+
+type Client struct {
+	Client *s3.Client
+	Bucket *string
+}
+
+func NewClient(ctx context.Context, s3Config *storepb.StorageS3Config) (*Client, error) {
+	cfg, err := config.LoadDefaultConfig(ctx,
+		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(s3Config.AccessKeyId, s3Config.AccessKeySecret, "")),
+		config.WithRegion(s3Config.Region),
+	)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to load s3 config")
+	}
+
+	client := s3.NewFromConfig(cfg, func(o *s3.Options) {
+		o.BaseEndpoint = aws.String(s3Config.Endpoint)
+		o.UsePathStyle = s3Config.UsePathStyle
+		o.RequestChecksumCalculation = aws.RequestChecksumCalculationWhenRequired
+		o.ResponseChecksumValidation = aws.ResponseChecksumValidationWhenRequired
+	})
+	return &Client{
+		Client: client,
+		Bucket: aws.String(s3Config.Bucket),
+	}, nil
+}
+
+// UploadObject uploads an object to S3.
+func (c *Client) UploadObject(ctx context.Context, key string, fileType string, content io.Reader) (string, error) {
+	uploader := manager.NewUploader(c.Client)
+	putInput := s3.PutObjectInput{
+		Bucket:      c.Bucket,
+		Key:         aws.String(key),
+		ContentType: aws.String(fileType),
+		Body:        content,
+	}
+	result, err := uploader.Upload(ctx, &putInput)
+	if err != nil {
+		return "", err
+	}
+
+	resultKey := result.Key
+	if resultKey == nil || *resultKey == "" {
+		return "", errors.New("failed to get file key")
+	}
+	return *resultKey, nil
+}
+
+// PresignGetObject presigns an object in S3.
+func (c *Client) PresignGetObject(ctx context.Context, key string) (string, error) {
+	presignClient := s3.NewPresignClient(c.Client)
+	presignResult, err := presignClient.PresignGetObject(ctx, &s3.GetObjectInput{
+		Bucket: aws.String(*c.Bucket),
+		Key:    aws.String(key),
+	}, func(opts *s3.PresignOptions) {
+		// Set the expiration time of the presigned URL to 5 days.
+		// Reference: https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html
+		opts.Expires = time.Duration(5 * 24 * time.Hour)
+	})
+	if err != nil {
+		return "", errors.Wrap(err, "failed to presign put object")
+	}
+	return presignResult.URL, nil
+}
+
+// GetObject retrieves an object from S3.
+func (c *Client) GetObject(ctx context.Context, key string) ([]byte, error) {
+	downloader := manager.NewDownloader(c.Client)
+	buffer := manager.NewWriteAtBuffer([]byte{})
+	_, err := downloader.Download(ctx, buffer, &s3.GetObjectInput{
+		Bucket: c.Bucket,
+		Key:    aws.String(key),
+	})
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to download object")
+	}
+	return buffer.Bytes(), nil
+}
+
+// GetObjectStream retrieves an object from S3 as a stream.
+func (c *Client) GetObjectStream(ctx context.Context, key string) (io.ReadCloser, error) {
+	output, err := c.Client.GetObject(ctx, &s3.GetObjectInput{
+		Bucket: c.Bucket,
+		Key:    aws.String(key),
+	})
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to get object")
+	}
+	return output.Body, nil
+}
+
+// DeleteObject deletes an object in S3.
+func (c *Client) DeleteObject(ctx context.Context, key string) error {
+	_, err := c.Client.DeleteObject(ctx, &s3.DeleteObjectInput{
+		Bucket: c.Bucket,
+		Key:    aws.String(key),
+	})
+	if err != nil {
+		return errors.Wrap(err, "failed to delete object")
+	}
+	return nil
+}

plugin/webhook/validate.go

@@ -0,0 +1,75 @@
+package webhook
+
+import (
+	"net"
+	"net/url"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+// reservedCIDRs lists IP ranges that must never be targeted by outbound webhook requests.
+// Covers loopback, RFC-1918 private, link-local (including cloud IMDS at 169.254.169.254),
+// and their IPv6 equivalents.
+var reservedCIDRs = []string{
+	"127.0.0.0/8",    // IPv4 loopback
+	"10.0.0.0/8",     // RFC-1918 class A
+	"172.16.0.0/12",  // RFC-1918 class B
+	"192.168.0.0/16", // RFC-1918 class C
+	"169.254.0.0/16", // Link-local / cloud IMDS
+	"::1/128",        // IPv6 loopback
+	"fc00::/7",       // IPv6 unique local
+	"fe80::/10",      // IPv6 link-local
+}
+
+// reservedNetworks is the parsed form of reservedCIDRs, built once at startup.
+var reservedNetworks []*net.IPNet
+
+func init() {
+	for _, cidr := range reservedCIDRs {
+		_, network, err := net.ParseCIDR(cidr)
+		if err != nil {
+			panic("webhook: invalid reserved CIDR " + cidr + ": " + err.Error())
+		}
+		reservedNetworks = append(reservedNetworks, network)
+	}
+}
+
+// isReservedIP reports whether ip falls within any reserved/private range.
+func isReservedIP(ip net.IP) bool {
+	for _, network := range reservedNetworks {
+		if network.Contains(ip) {
+			return true
+		}
+	}
+	return false
+}
+
+// ValidateURL checks that rawURL:
+//  1. Parses as a valid absolute URL.
+//  2. Uses the http or https scheme.
+//  3. Does not resolve to a reserved/private IP address.
+//
+// It returns a gRPC InvalidArgument status error so callers can return it directly.
+func ValidateURL(rawURL string) error {
+	u, err := url.ParseRequestURI(rawURL)
+	if err != nil {
+		return status.Errorf(codes.InvalidArgument, "invalid webhook URL: %v", err)
+	}
+	if u.Scheme != "http" && u.Scheme != "https" {
+		return status.Errorf(codes.InvalidArgument, "webhook URL must use http or https scheme, got %q", u.Scheme)
+	}
+
+	ips, err := net.LookupHost(u.Hostname())
+	if err != nil {
+		return status.Errorf(codes.InvalidArgument, "webhook URL hostname could not be resolved: %v", err)
+	}
+
+	for _, ipStr := range ips {
+		ip := net.ParseIP(ipStr)
+		if ip != nil && isReservedIP(ip) {
+			return status.Errorf(codes.InvalidArgument, "webhook URL must not resolve to a reserved or private IP address")
+		}
+	}
+	return nil
+}

plugin/webhook/webhook.go

@@ -0,0 +1,120 @@
+package webhook
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/pkg/errors"
+
+	v1pb "github.com/usememos/memos/proto/gen/api/v1"
+)
+
+var (
+	// timeout is the timeout for webhook request. Default to 30 seconds.
+	timeout = 30 * time.Second
+
+	// safeClient is the shared HTTP client used for all webhook dispatches.
+	// Its Transport guards against SSRF by blocking connections to reserved/private
+	// IP addresses at dial time, which also defeats DNS rebinding attacks.
+	safeClient = &http.Client{
+		Timeout: timeout,
+		Transport: &http.Transport{
+			DialContext: safeDialContext,
+		},
+	}
+)
+
+// safeDialContext is a net.Dialer.DialContext replacement that resolves the target
+// hostname and rejects any address that falls within a reserved/private IP range.
+func safeDialContext(ctx context.Context, network, addr string) (net.Conn, error) {
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return nil, errors.Errorf("webhook: invalid address %q", addr)
+	}
+
+	ips, err := net.DefaultResolver.LookupHost(ctx, host)
+	if err != nil {
+		return nil, errors.Wrapf(err, "webhook: failed to resolve host %q", host)
+	}
+
+	for _, ipStr := range ips {
+		if ip := net.ParseIP(ipStr); ip != nil && isReservedIP(ip) {
+			return nil, errors.Errorf("webhook: connection to reserved/private IP address is not allowed")
+		}
+	}
+
+	return (&net.Dialer{}).DialContext(ctx, network, net.JoinHostPort(host, port))
+}
+
+type WebhookRequestPayload struct {
+	// The target URL for the webhook request.
+	URL string `json:"url"`
+	// The type of activity that triggered this webhook.
+	ActivityType string `json:"activityType"`
+	// The resource name of the creator. Format: users/{user}
+	Creator string `json:"creator"`
+	// The memo that triggered this webhook (if applicable).
+	Memo *v1pb.Memo `json:"memo"`
+}
+
+// Post posts the message to webhook endpoint.
+func Post(requestPayload *WebhookRequestPayload) error {
+	body, err := json.Marshal(requestPayload)
+	if err != nil {
+		return errors.Wrapf(err, "failed to marshal webhook request to %s", requestPayload.URL)
+	}
+
+	req, err := http.NewRequest("POST", requestPayload.URL, bytes.NewBuffer(body))
+	if err != nil {
+		return errors.Wrapf(err, "failed to construct webhook request to %s", requestPayload.URL)
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := safeClient.Do(req)
+	if err != nil {
+		return errors.Wrapf(err, "failed to post webhook to %s", requestPayload.URL)
+	}
+	defer resp.Body.Close()
+
+	b, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return errors.Wrapf(err, "failed to read webhook response from %s", requestPayload.URL)
+	}
+
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		return errors.Errorf("failed to post webhook %s, status code: %d", requestPayload.URL, resp.StatusCode)
+	}
+
+	response := &struct {
+		Code    int    `json:"code"`
+		Message string `json:"message"`
+	}{}
+	if err := json.Unmarshal(b, response); err != nil {
+		return errors.Wrapf(err, "failed to unmarshal webhook response from %s", requestPayload.URL)
+	}
+
+	if response.Code != 0 {
+		return errors.Errorf("receive error code sent by webhook server, code %d, msg: %s", response.Code, response.Message)
+	}
+
+	return nil
+}
+
+// PostAsync posts the message to webhook endpoint asynchronously.
+// It spawns a new goroutine to handle the request and does not wait for the response.
+func PostAsync(requestPayload *WebhookRequestPayload) {
+	go func() {
+		if err := Post(requestPayload); err != nil {
+			slog.Warn("Failed to dispatch webhook asynchronously",
+				slog.String("url", requestPayload.URL),
+				slog.String("activityType", requestPayload.ActivityType),
+				slog.Any("err", err))
+		}
+	}()
+}

plugin/webhook/webhook_test.go

@@ -0,0 +1 @@
+package webhook