Fix addnext failing on an empty queue

Previously, addnext would try to unconditionally add at index one into a
queue. This panicked if the queue was empty. Added two protections, one
that checks the index in the InsertTrack function, the other in the
addnext command itself to insert at zero if the queue is empty.

bot/queue.go

@@ -85,6 +85,11 @@ func (q *Queue) InsertTrack(i int, t interfaces.Track) error {
 	q.mutex.Lock()
 	beforeLen := len(q.Queue)
 
+	if i < 0 || i > beforeLen {
+		q.mutex.Unlock()
+		return errors.New("Adding at invalid index in queue")
+	}
+
 	// An error should never occur here since maxTrackDuration is restricted to
 	// ints. Any error in the configuration will be caught during yaml load.
 	maxTrackDuration, _ := time.ParseDuration(fmt.Sprintf("%ds",

commands/addnext.go

@@ -75,7 +75,11 @@ func (c *AddNextCommand) Execute(user *gumble.User, args ...string) (string, boo
 	numAdded := 0
 	// We must loop backwards here to preserve the track order when inserting tracks.
 	for i := len(allTracks) - 1; i >= 0; i-- {
-		if err = DJ.Queue.InsertTrack(1, allTracks[i]); err != nil {
+		insertIndex := 1
+		if DJ.Queue.Length() == 0 {
+			insertIndex = 0
+		}
+		if err = DJ.Queue.InsertTrack(insertIndex, allTracks[i]); err != nil {
 			numTooLong++
 		} else {
 			numAdded++

commands/addnext_test.go

@@ -6,3 +6,5 @@
  */
 
 package commands
+
+// TODO: Add regression test for bug where addnext fails on an empty queue.