first commit

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.