watch tag job

trigger/poll/watcher.go

@@ -18,3 +18,51 @@ type RepositoryWatcher struct {
 
 	cron *cron.Cron
 }
+// Watch specific tag job
+type WatchTagJob struct {
+	providers      provider.Providers
+	registryClient registry.Client
+	details        *watchDetails
+}
+
+func NewWatchTagJob(providers provider.Providers, registryClient registry.Client, details *watchDetails) *WatchTagJob {
+	return &WatchTagJob{
+		providers:      providers,
+		registryClient: registryClient,
+		details:        details,
+	}
+}
+
+func (j *WatchTagJob) Run() {
+	currentDigest, err := j.registryClient.Digest(registry.Opts{
+		Registry: j.details.imageRef.Registry(),
+		Name:     j.details.imageRef.ShortName(),
+		Tag:      j.details.imageRef.Tag(),
+	})
+
+	if err != nil {
+		log.WithFields(log.Fields{
+			"error": err,
+			"image": j.details.imageRef.Remote(),
+		}).Error("trigger.poll.WatchTagJob: failed to check digest")
+		return
+	}
+
+	// checking whether image digest has changed
+	if j.details.digest != currentDigest {
+		// updating digest
+		j.details.digest = currentDigest
+
+		event := types.Event{
+			Repository: types.Repository{
+				Name:   j.details.imageRef.Remote(),
+				Tag:    j.details.imageRef.Tag(),
+				Digest: currentDigest,
+			},
+			TriggerName: types.TriggerTypePoll.String(),
+		}
+
+		j.providers.Submit(event)
+
+	}
+}