Ji, just sharing my thoughts here. Personally I think the use of queue_items.count + 1 will cause trouble in later implementation. Try the following steps in your app:
* Add 5 videos to My Queue
* Remove the first 4 video in My Queue 
* With the last video remaining in My Queue which has a position 5
* Add another video to My Queue
* The newly added video listed before the remaining one!
But I was having trouble come up with a good spec for this case. I guess that's something we'll address in the later course.