playback: move most ops to player

This allows me to handle foreign MediaItem events easily. Not tested,
don't have time.

app/src/main/java/org/oxycblt/auxio/playback/state/PlaybackStateHolder.kt

@@ -53,13 +53,8 @@ interface PlaybackStateHolder {
 
     /**
      * Applies a completely new playback state to the holder.
-     *
-     * @param queue The new queue to use.
-     * @param start The song to start playback from. Should be in the queue.
-     * @param parent The parent to play from.
-     * @param shuffled Whether the queue should be shuffled.
      */
-    fun newPlayback(queue: List<Song>, start: Song?, parent: MusicParent?, shuffled: Boolean)
+    fun newPlayback(command: PlaybackCommand)
 
     /**
      * Update the playing state of the audio player.

app/src/main/java/org/oxycblt/auxio/playback/state/PlaybackStateManager.kt

@@ -438,15 +438,11 @@ class PlaybackStateManagerImpl @Inject constructor() : PlaybackStateManager {
 
     @Synchronized
     override fun play(command: PlaybackCommand) {
-        play(command.song, command.parent, command.queue, command.shuffled)
-    }
-
-    private fun play(song: Song?, parent: MusicParent?, queue: List<Song>, shuffled: Boolean) {
         val stateHolder = stateHolder ?: return
-        logD("Playing ${song} from $parent in ${queue.size}-song queue [shuffled=${shuffled}]")
+        logD("Playing $command")
         // Played something, so we are initialized now
         isInitialized = true
-        stateHolder.newPlayback(queue, song, parent, shuffled)
+        stateHolder.newPlayback(command)
     }
 
     // --- QUEUE FUNCTIONS ---
@@ -476,7 +472,7 @@ class PlaybackStateManagerImpl @Inject constructor() : PlaybackStateManager {
     override fun playNext(songs: List<Song>) {
         if (currentSong == null) {
             logD("Nothing playing, short-circuiting to new playback")
-            play(null, null, songs, false)
+            play(QueueCommand(songs))
         } else {
             val stateHolder = stateHolder ?: return
             logD("Adding ${songs.size} songs to start of queue")
@@ -488,7 +484,7 @@ class PlaybackStateManagerImpl @Inject constructor() : PlaybackStateManager {
     override fun addToQueue(songs: List<Song>) {
         if (currentSong == null) {
             logD("Nothing playing, short-circuiting to new playback")
-            play(null, null, songs, false)
+            play(QueueCommand(songs))
         } else {
             val stateHolder = stateHolder ?: return
             logD("Adding ${songs.size} songs to end of queue")
@@ -496,6 +492,12 @@ class PlaybackStateManagerImpl @Inject constructor() : PlaybackStateManager {
         }
     }
 
+    private class QueueCommand(override val queue: List<Song>) : PlaybackCommand  {
+        override val song: Song? = null
+        override val parent: MusicParent? = null
+        override val shuffled = false
+    }
+
     @Synchronized
     override fun moveQueueItem(src: Int, dst: Int) {
         val stateHolder = stateHolder ?: return