Fix bug when media switches on the chromecast

There is a bug when the chromecast changes media application, and
'go-chromecast' woudl try and write to the 'mediaFinished' channel
regardless of whether it was initialised or not. This is because of the
poor design of the internals, the 'mediaFinished' is littered throughout
the codebase but is only relevant to the 'load' command. This needs some
cleaning up in a future refactor. For now just fix the bug by not
writing to the channel if it hasn't been initialised.

Updates: #70

Author: vishen

application/application.go

@@ -169,6 +169,28 @@ func (a *Application) messageChanHandler() {
 	}
 }
 
+// TODO: Clean-up: these Media* methods are a hack around trying
+// to use the mediaFinished channel when it hasn't been properly
+// set up. This is happening because there is some instances where we don't
+// have any running media ('watch' command) but yet the 'mediaFinished'
+// is littered throughout the codebase since. This needs a redesign now that
+// we do things other than just loading and playing media files.
+func (a *Application) MediaStart() {
+	a.mediaFinished = make(chan bool, 1)
+}
+
+func (a *Application) MediaWait() {
+	<-a.mediaFinished
+	a.mediaFinished = nil
+}
+
+func (a *Application) MediaFinished() {
+	if a.mediaFinished == nil {
+		return
+	}
+	a.mediaFinished <- true
+}
+
 func (a *Application) recvMessages() {
 	for msg := range a.recvMsgChan {
 		requestID, err := jsonparser.GetInt([]byte(*msg.PayloadUtf8), "requestId")
@@ -186,19 +208,19 @@ func (a *Application) recvMessages() {
 		messageType, _ := jsonparser.GetString(messageBytes, "type")
 		switch messageType {
 		case "LOAD_FAILED":
-			a.mediaFinished <- true
+			a.MediaFinished()
 		case "MEDIA_STATUS":
 			resp := cast.MediaStatusResponse{}
 			if err := json.Unmarshal(messageBytes, &resp); err == nil {
 				for _, status := range resp.Status {
 					// The LoadingItemId is only set when there is a playlist and there
 					// is an item being loaded to play next.
 					if status.IdleReason == "FINISHED" && status.LoadingItemId == 0 {
-						a.mediaFinished <- true
+						a.MediaFinished()
 					} else if status.IdleReason == "INTERRUPTED" && status.Media.ContentId == "" {
 						// This can happen when we go "next" in a playlist when it
 						// is playing the last track.
-						a.mediaFinished <- true
+						a.MediaFinished()
 					}
 				}
 			}
@@ -214,7 +236,7 @@ func (a *Application) recvMessages() {
 				// it because that currently isn't possible.
 				for _, app := range resp.Status.Applications {
 					if app.AppId != a.application.AppId {
-						a.mediaFinished <- true
+						a.MediaFinished()
 					}
 					a.application = &app
 				}
@@ -276,6 +298,7 @@ func (a *Application) Update() error {
 		if err == nil {
 			break
 		}
+		a.log("error getting receiever status: %v", err)
 		a.log("unable to get status from device; attempt %d/5, retrying...", i+1)
 		time.Sleep(time.Second * 2)
 	}
@@ -608,7 +631,7 @@ func (a *Application) Load(filenameOrUrl, contentType string, transcode, detach
 	}
 
 	// NOTE: This isn't concurrent safe, but it doesn't need to be at the moment!
-	a.mediaFinished = make(chan bool, 1)
+	a.MediaStart()
 
 	// Send the command to the chromecast
 	a.sendMediaRecv(&cast.LoadMediaCommand{
@@ -629,7 +652,7 @@ func (a *Application) Load(filenameOrUrl, contentType string, transcode, detach
 	}
 
 	// Wait until we have been notified that the media has finished playing
-	<-a.mediaFinished
+	a.MediaWait()
 	return nil
 }
 
@@ -667,7 +690,9 @@ func (a *Application) QueueLoad(filenames []string, contentType string, transcod
 	})
 
 	// Wait until we have been notified that the media has finished playing
-	<-a.mediaFinished
+	// TODO: This does nothing. This hasn't been initialised and just blocks
+	// forever.
+	a.MediaWait()
 	return nil
 }
 
@@ -752,7 +777,9 @@ func (a *Application) Slideshow(filenames []string, duration int, repeat bool) e
 			if err := a.Next(); err != nil {
 				return err
 			}
-		// Media has finished playing
+		// Media has finished playing.
+		// TODO: Hack, how to ensure this is always possible
+		// to wait on.
 		case <-a.mediaFinished:
 			return nil
 		}