Add --print-delta-and-exit, refactor

README.md

@@ -42,6 +42,8 @@ Usage of wait-for-cron-expression-match:
     	Print dots to stdout while waiting
   -format string
     	Timestamp format (default "2006-01-02T15:04:05Z07:00")
+  -print-delta-and-exit
+    	Only print the duration (in seconds) until the next expression match and exit (without waiting)
   -print-next-match-and-exit
     	Only print the timestamp of the next expression match and exit (without waiting)
   -q	(alias for -quiet)

main.go

@@ -14,9 +14,10 @@ var config struct {
 	Quiet                     bool
 	PrintDots                 bool
 	PrintNextTimestampAndExit bool
+	PrintDeltaAndExit         bool
 	TimestampFormat           string
+	CronExpressions           []string
 
-	cronExpressions    []string
 	schedules          []cron.Schedule
 	evaluationInterval time.Duration
 }
@@ -27,6 +28,7 @@ func init() {
 	log.SetFlags(log.Ltime | log.Ldate | log.Lmicroseconds)
 	log.SetPrefix(fmt.Sprintf("[%s] ", app))
 	config.TimestampFormat = time.RFC3339
+	flag.BoolVar(&config.PrintDeltaAndExit, "print-delta-and-exit", config.PrintDeltaAndExit, "Only print the duration (in seconds) until the next expression match and exit (without waiting)")
 	flag.BoolVar(&config.PrintNextTimestampAndExit, "print-next-match-and-exit", config.PrintNextTimestampAndExit, "Only print the timestamp of the next expression match and exit (without waiting)")
 	flag.StringVar(&config.TimestampFormat, "format", config.TimestampFormat, "Timestamp format")
 	flag.BoolVar(&config.Quiet, "quiet", config.Quiet, "Suppress all output")
@@ -35,13 +37,13 @@ func init() {
 	flag.Parse()
 
 	config.evaluationInterval = 1 * time.Second
-	config.cronExpressions = flag.Args()
+	config.CronExpressions = flag.Args()
 
-	if len(config.cronExpressions) == 0 {
+	if len(config.CronExpressions) == 0 {
 		log.Fatal("at least one expression is required")
 	}
 	parser := cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor)
-	for _, e := range config.cronExpressions {
+	for _, e := range config.CronExpressions {
 		schedule, err := parser.Parse(e)
 		if err != nil {
 			log.Fatalf("parse cron expression %q: %v", e, err)
@@ -57,39 +59,56 @@ func init() {
 
 func main() {
 	now := time.Now()
-	tickInterval := config.evaluationInterval
-	var next time.Time
-	for i, s := range config.schedules {
-		nextNew := s.Next(now)
-		if i == 0 || nextNew.Before(next) {
-			next = nextNew
-		}
+	next := nextMatch(now)
+	if config.PrintDeltaAndExit {
+		fmt.Println(time.Until(next).Seconds())
+		return
 	}
 	if config.PrintNextTimestampAndExit {
 		fmt.Println(next.Format(config.TimestampFormat))
 		return
 	}
-	delta := next.Sub(now)
+	waitUntil(next)
+}
+
+func waitUntil(next time.Time) {
+	defer func() {
+		if config.PrintDots {
+			fmt.Println()
+		}
+		log.Print("done")
+	}()
+
+	tickInterval := config.evaluationInterval
+	delta := time.Until(next)
 	if delta < tickInterval {
 		tickInterval = delta
 	}
 	tick := time.Tick(tickInterval)
 
 	plural := ""
-	if len(config.cronExpressions) > 1 {
+	if len(config.CronExpressions) > 1 {
 		plural = "s"
 	}
-	log.Printf("waiting %v until next match (%v) of cron expression%s %q", delta, next.Format(time.RFC3339Nano), plural, config.cronExpressions)
-	defer log.Print("done")
-	for now = range tick {
+	log.Printf("waiting %v until next match (%v) of cron expression%s %q", time.Until(next), next.Format(config.TimestampFormat), plural, config.CronExpressions)
+
+	for now := range tick {
 		if config.PrintDots {
 			fmt.Print(".")
 		}
 		if now.After(next) {
-			if config.PrintDots {
-				fmt.Println()
-			}
 			return
 		}
 	}
 }
+
+func nextMatch(now time.Time) time.Time {
+	var next time.Time
+	for i, s := range config.schedules {
+		nextNew := s.Next(now)
+		if i == 0 || nextNew.Before(next) {
+			next = nextNew
+		}
+	}
+	return next
+}