Add cron schedules and sync docs

agent/internal/scheduler/scheduler.go

@@ -11,6 +11,8 @@ import (
 	"github.com/monlet/agent/internal/runner"
 )
 
+var parseCronSchedule = config.ParseCronSchedule
+
 // Event is a contract-shaped check result emitted by the scheduler.
 type Event struct {
 	EventID              string    `json:"event_id"`
@@ -207,8 +209,10 @@ func (w *checkWorker) loop(initial config.CheckConfig) {
 		w.wg.Done()
 	}()
 	cfg := initial
-	t := time.NewTicker(cfg.Interval.Duration)
+	t := time.NewTimer(time.Hour)
+	stopTimer(t)
 	defer t.Stop()
+	var timerCh <-chan time.Time
 
 	running := false
 	stopping := false
@@ -230,7 +234,26 @@ func (w *checkWorker) loop(initial config.CheckConfig) {
 		}()
 	}
 
-	start(cfg)
+	arm := func(c config.CheckConfig, immediateInterval bool) bool {
+		delay, err := nextDelay(c, time.Now(), immediateInterval)
+		if err != nil {
+			return false
+		}
+		resetTimer(t, delay)
+		timerCh = t.C
+		return true
+	}
+	disarm := func() {
+		stopTimer(t)
+		timerCh = nil
+	}
+
+	if !arm(cfg, true) {
+		if w.hooks.OnStopped != nil {
+			w.hooks.OnStopped(cfg.ID)
+		}
+		return
+	}
 
 	for {
 		select {
@@ -257,11 +280,21 @@ func (w *checkWorker) loop(initial config.CheckConfig) {
 				continue
 			}
 			cfg = next
-			t.Reset(cfg.Interval.Duration)
+			if cfg.UsesCron() {
+				runAfterCurrent = false
+				if !arm(cfg, false) {
+					return
+				}
+				continue
+			}
 			if running {
 				runAfterCurrent = true
+				disarm()
 			} else {
 				start(cfg)
+				if !arm(cfg, false) {
+					return
+				}
 			}
 		case <-w.doneCh:
 			running = false
@@ -281,26 +314,35 @@ func (w *checkWorker) loop(initial config.CheckConfig) {
 			}
 			if runAfterCurrent {
 				runAfterCurrent = false
+				startAfterDrain := true
 				for {
 					select {
 					case next := <-w.updateCh:
 						if !reflect.DeepEqual(cfg, next) {
 							cfg = next
-							t.Reset(cfg.Interval.Duration)
+							startAfterDrain = !cfg.UsesCron()
 						}
 					default:
-						start(cfg)
+						if startAfterDrain {
+							start(cfg)
+						}
+						if !arm(cfg, false) {
+							return
+						}
 						goto nextLoop
 					}
 				}
 			nextLoop:
 				continue
 			}
-		case <-t.C:
+		case <-timerCh:
 			if stopping {
 				continue
 			}
 			start(cfg)
+			if !arm(cfg, false) {
+				return
+			}
 		}
 	}
 }
@@ -358,3 +400,41 @@ func incidentKey(agentID string, c config.CheckConfig) string {
 	}
 	return agentID + ":" + c.ID
 }
+
+func nextDelay(c config.CheckConfig, now time.Time, immediateInterval bool) (time.Duration, error) {
+	if c.UsesCron() {
+		schedule, err := parseCronSchedule(c.Cron)
+		if err != nil {
+			return 0, err
+		}
+		return delayUntil(now, schedule.Next(now)), nil
+	}
+	if immediateInterval {
+		return 0, nil
+	}
+	return c.Interval.Duration, nil
+}
+
+func delayUntil(now, next time.Time) time.Duration {
+	if next.Before(now) {
+		return 0
+	}
+	return next.Sub(now)
+}
+
+func resetTimer(t *time.Timer, d time.Duration) {
+	if d < 0 {
+		d = 0
+	}
+	stopTimer(t)
+	t.Reset(d)
+}
+
+func stopTimer(t *time.Timer) {
+	if !t.Stop() {
+		select {
+		case <-t.C:
+		default:
+		}
+	}
+}