playback: make mediasession rely on exoplayer

Make PlaybackSessionConnector also take events from ExoPlayer as it
used to with MediaSessionConnector. This improves reliability
somewhat at the cost of making the code even more hideous.

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

@@ -234,8 +234,8 @@ class PlaybackStateManager private constructor() {
     private fun updatePlayback(song: Song, shouldPlay: Boolean = true) {
         mIsInUserQueue = false
 
-        mPosition = 0
         mSong = song
+        mPosition = 0
 
         setPlaying(shouldPlay)
     }

app/src/main/java/org/oxycblt/auxio/playback/system/PlaybackService.kt

@@ -112,7 +112,7 @@ class PlaybackService : Service(), Player.Listener, PlaybackStateManager.Callbac
             isActive = true
         }
 
-        connector = PlaybackSessionConnector(this, mediaSession)
+        connector = PlaybackSessionConnector(this, player, mediaSession)
 
         // Then the notif/headset callbacks
         IntentFilter().apply {
@@ -204,6 +204,12 @@ class PlaybackService : Service(), Player.Listener, PlaybackStateManager.Callbac
         playbackManager.next()
     }
 
+    override fun onPositionDiscontinuity(reason: Int) {
+        if (reason == Player.DISCONTINUITY_REASON_SEEK) {
+            playbackManager.setPosition(player.currentPosition)
+        }
+    }
+
     // --- PLAYBACK STATE CALLBACK OVERRIDES ---
 
     override fun onSongUpdate(song: Song?) {

app/src/main/java/org/oxycblt/auxio/playback/system/PlaybackSessionConnector.kt

@@ -6,21 +6,28 @@ import android.os.SystemClock
 import android.support.v4.media.MediaMetadataCompat
 import android.support.v4.media.session.MediaSessionCompat
 import android.support.v4.media.session.PlaybackStateCompat
+import com.google.android.exoplayer2.Player
 import org.oxycblt.auxio.coil.loadBitmap
 import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.playback.state.LoopMode
 import org.oxycblt.auxio.playback.state.PlaybackStateManager
 
+/**
+ * Nightmarish class that coordinates communication between [MediaSessionCompat], [Player],
+ * and [PlaybackStateManager]
+ */
 class PlaybackSessionConnector(
     private val context: Context,
+    private val player: Player,
     private val mediaSession: MediaSessionCompat
-) : PlaybackStateManager.Callback, MediaSessionCompat.Callback() {
+) : PlaybackStateManager.Callback, Player.Listener, MediaSessionCompat.Callback() {
     private val playbackManager = PlaybackStateManager.getInstance()
     private val emptyMetadata = MediaMetadataCompat.Builder().build()
 
     init {
         mediaSession.setCallback(this)
         playbackManager.addCallback(this)
+        player.addListener(this)
 
         onSongUpdate(playbackManager.song)
         onPlayingUpdate(playbackManager.isPlaying)
@@ -28,6 +35,7 @@ class PlaybackSessionConnector(
 
     fun release() {
         playbackManager.removeCallback(this)
+        player.removeListener(this)
     }
 
     // --- MEDIASESSION CALLBACKS ---
@@ -49,7 +57,7 @@ class PlaybackSessionConnector(
     }
 
     override fun onSeekTo(position: Long) {
-        playbackManager.seekTo(position)
+        player.seekTo(position)
     }
 
     override fun onRewind() {
@@ -83,8 +91,6 @@ class PlaybackSessionConnector(
     // --- PLAYBACKSTATEMANAGER CALLBACKS ---
 
     override fun onSongUpdate(song: Song?) {
-        invalidateSessionState()
-
         if (song == null) {
             mediaSession.setMetadata(emptyMetadata)
             return
@@ -110,19 +116,32 @@ class PlaybackSessionConnector(
         invalidateSessionState()
     }
 
-    override fun onSeek(position: Long) {
+    // --
-        invalidateSessionState()
+
+    override fun onEvents(player: Player, events: Player.Events) {
+        if (events.containsAny(
+                Player.EVENT_POSITION_DISCONTINUITY,
+                Player.EVENT_PLAYBACK_STATE_CHANGED,
+                Player.EVENT_PLAY_WHEN_READY_CHANGED,
+                Player.EVENT_IS_PLAYING_CHANGED,
+                Player.EVENT_REPEAT_MODE_CHANGED,
+                Player.EVENT_PLAYBACK_PARAMETERS_CHANGED
+            )
+        ) {
+            invalidateSessionState()
+        }
     }
 
     // --- MISC ---
 
     private fun invalidateSessionState() {
-        // Position updates arrive faster when you upload STATE_PAUSED for some inane reason.
+        // Position updates arrive faster when you upload STATE_PAUSED for some insane reason.
         val state = PlaybackStateCompat.Builder()
             .setActions(ACTIONS)
+            .setBufferedPosition(player.bufferedPosition)
             .setState(
                 PlaybackStateCompat.STATE_PAUSED,
-                playbackManager.position,
+                player.currentPosition,
                 1.0f,
                 SystemClock.elapsedRealtime()
             )
@@ -131,7 +150,7 @@ class PlaybackSessionConnector(
 
         state.setState(
             getPlayerState(),
-            playbackManager.position,
+            player.currentPosition,
             1.0f,
             SystemClock.elapsedRealtime()
         )