Add Prev time record to the entry

Prev records the previous time (if any) that the job was run.

cron.go

@@ -27,6 +27,7 @@ type Job interface {
 type Entry struct {
 	*Schedule
 	Next time.Time
+	Prev time.Time
 	Job  Job
 }
 
@@ -67,7 +68,10 @@ func (c *Cron) AddFunc(spec string, cmd func()) {
 }
 
 func (c *Cron) AddJob(spec string, cmd Job) {
-	entry := &Entry{Parse(spec), time.Time{}, cmd}
+	entry := &Entry{
+		Schedule: Parse(spec),
+		Job:      cmd,
+	}
 	if !c.running {
 		c.entries = append(c.entries, entry)
 		return
@@ -121,6 +125,7 @@ func (c *Cron) run() {
 					break
 				}
 				go e.Job.Run()
+				e.Prev = e.Next
 				e.Next = e.Schedule.Next(effective)
 			}
 
@@ -145,7 +150,12 @@ func (c *Cron) Stop() {
 func (c *Cron) entrySnapshot() []*Entry {
 	entries := []*Entry{}
 	for _, e := range c.entries {
-		entries = append(entries, &Entry{e.Schedule, e.Next, e.Job})
+		entries = append(entries, &Entry{
+			Schedule: e.Schedule,
+			Next:     e.Next,
+			Prev:     e.Prev,
+			Job:      e.Job,
+		})
 	}
 	return entries
 }