feat: remove chain, use options for execution overlap strategies

cron.go

@@ -25,7 +25,7 @@ type removal struct {
 // be inspected while running.
 type Cron struct {
 	entries          entryHeap
-	chain            Chain
+	overlap          func(func(), *slog.Logger) func()
 	stop             chan struct{}
 	add              chan insertion
 	remove           chan removal
@@ -90,7 +90,7 @@ type Entry struct {
 func New(opts ...Option) *Cron {
 	c := &Cron{
 		entries:          entryHeap{},
-		chain:            NewChain(),
+		overlap:          func(cmd func(), logger *slog.Logger) func() { return cmd },
 		add:              make(chan insertion),
 		stop:             make(chan struct{}),
 		snapshot:         make(chan chan []Entry),
@@ -130,11 +130,12 @@ func (c *Cron) Schedule(schedule Schedule, cmd func()) (ID, error) {
 		return 0, fmt.Errorf("run out of available ids")
 	}
 
+	logger := c.logger.With("id", c.next)
 	entry := &Entry{
 		ID:       c.next,
 		Schedule: schedule,
-		job:      c.chain.Then(cmd),
-		logger:   c.logger.With("id", c.next),
+		job:      c.overlap(cmd, logger),
+		logger:   logger,
 	}
 	c.next++
 	if !c.running {

option.go

@@ -2,6 +2,8 @@ package cron
 
 import (
 	"log/slog"
+	"sync"
+	"time"
 )
 
 // Option represents a modification to the default behavior of a Cron.
@@ -22,14 +24,6 @@ func WithParser(p Parser) Option {
 	}
 }
 
-// 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 *slog.Logger) Option {
 	return func(c *Cron) {
@@ -54,3 +48,37 @@ func WithOnCycleCompleted(f func()) Option {
 		c.onCycleCompleted = append(c.onCycleCompleted, f)
 	}
 }
+
+func WithSkipIfRunning() Option {
+	return func(c *Cron) {
+		c.overlap = func(cmd func(), logger *slog.Logger) func() {
+			var ch = make(chan struct{}, 1)
+			ch <- struct{}{}
+			return func() {
+				select {
+				case v := <-ch:
+					defer func() { ch <- v }()
+				default:
+					logger.Info("job execution skipped", "event", "skip")
+				}
+			}
+		}
+	}
+}
+
+func WithQueueIfStillRunning() Option {
+	return func(c *Cron) {
+		c.overlap = func(cmd func(), logger *slog.Logger) func() {
+			var mu sync.Mutex
+			return func() {
+				start := time.Now()
+				mu.Lock()
+				defer mu.Unlock()
+				if dur := time.Since(start); dur > time.Minute {
+					logger.Info("job execution delayed", "event", "delay", "duration", dur)
+				}
+				cmd()
+			}
+		}
+	}
+}