playback: fix queue adding with one-song queues

Fix an issue where with queues of one-song, adding another song with
"Play next" results in it going behind the current song. This stemmed
from a fix for a crash with empty queues, so instead of doing some
insane min/max logic we just check if the queue is empty and just don't
add the item if it is. It will only get overwritten anyway.

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

@@ -30,8 +30,6 @@ import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.settings.SettingsManager
 import org.oxycblt.auxio.util.logD
 import org.oxycblt.auxio.util.logE
-import kotlin.math.max
-import kotlin.math.min
 
 /**
  * Master class (and possible god object) for the playback state.
@@ -319,7 +317,11 @@ class PlaybackStateManager private constructor() {
      * Add a [song] to the top of the queue.
      */
     fun playNext(song: Song) {
-        mQueue.add(min(mIndex + 1, max(mQueue.lastIndex, 0)), song)
+        if (mQueue.isEmpty()) {
+            return
+        }
+
+        mQueue.add(mIndex + 1, song)
         pushQueueUpdate()
     }
 
@@ -327,7 +329,11 @@ class PlaybackStateManager private constructor() {
      * Add a list of [songs] to the top of the queue.
      */
     fun playNext(songs: List<Song>) {
-        mQueue.addAll(min(mIndex + 1, max(mQueue.lastIndex, 0)), songs)
+        if (mQueue.isEmpty()) {
+            return
+        }
+
+        mQueue.addAll(mIndex + 1, songs)
         pushQueueUpdate()
     }
 

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

@@ -43,6 +43,7 @@ class AudioReactor(
     private val callback: (Float) -> Unit
 ) : AudioManager.OnAudioFocusChangeListener, SettingsManager.Callback {
     private data class Gain(val track: Float, val album: Float)
+    private data class GainTag(val key: String, val value: Float)
 
     private val playbackManager = PlaybackStateManager.getInstance()
     private val settingsManager = SettingsManager.getInstance()
@@ -60,6 +61,8 @@ class AudioReactor(
         .build()
 
     private var pauseWasTransient = false
+
+    // It's good to keep the volume and the ducking multiplier separate so that we can
     private var multiplier = 1f
         set(value) {
             field = value
@@ -103,17 +106,21 @@ class AudioReactor(
                 return
             }
 
-            // User wants track gain to be preferred
+            // User wants track gain to be preferred. Default to album gain only if there
+            // is no track gain.
             ReplayGainMode.TRACK ->
                 { gain ->
                     gain.track == 0f
                 }
 
+            // User wants album gain to be preferred. Default to track gain only if there
+            // is no album gain.
             ReplayGainMode.ALBUM ->
                 { gain ->
                     gain.album != 0f
                 }
 
+            // User wants album gain to be used when in an album, track gain otherwise.
             ReplayGainMode.DYNAMIC ->
                 { _ ->
                     playbackManager.parent is Album &&
@@ -131,6 +138,7 @@ class AudioReactor(
                 gain.track
             }
         } else {
+            // No gain tags were present
             0f
         }
 
@@ -140,8 +148,6 @@ class AudioReactor(
     }
 
     private fun parseReplayGain(metadata: Metadata): Gain? {
-        data class GainTag(val key: String, val value: Float)
-
         var trackGain = 0f
         var albumGain = 0f
         var found = false
@@ -213,7 +219,7 @@ class AudioReactor(
     }
 
     /**
-     * Abandon the current focus request, functionally "Destroying it".
+     * Abandon the current focus request and any callbacks
      */
     fun release() {
         AudioManagerCompat.abandonAudioFocusRequest(audioManager, request)