music: fix enqueueing

Fix enqueuing issues encountered during testing.

app/src/main/java/org/oxycblt/auxio/playback/replaygain/ReplayGainAudioProcessor.kt

@@ -242,13 +242,7 @@ class ReplayGainAudioProcessor(private val context: Context) :
         } else {
             for (i in pos until limit step 2) {
                 // 16-bit PCM audio, deserialize a little-endian short.
-                var sample =
-                    inputBuffer
-                        .get(i + 1)
-                        .toInt()
-                        .shl(8)
-                        .or(inputBuffer.get(i).toInt().and(0xFF))
-                        .toShort()
+                var sample = inputBuffer.getLeShort(i)
                 // Ensure we clamp the values to the minimum and maximum values possible
                 // for the encoding. This prevents issues where samples amplified beyond
                 // 1 << 16 will end up becoming truncated during the conversion to a short,
@@ -259,7 +253,7 @@ class ReplayGainAudioProcessor(private val context: Context) :
                         .coerceAtLeast(Short.MIN_VALUE.toInt())
                         .coerceAtMost(Short.MAX_VALUE.toInt())
                         .toShort()
-                buffer.put(sample.toByte()).put(sample.toInt().shr(8).toByte())
+                buffer.putLeShort(sample)
             }
         }
 
@@ -267,6 +261,22 @@ class ReplayGainAudioProcessor(private val context: Context) :
         buffer.flip()
     }
 
+    /**
+     * Always read a little-endian [Short] from the [ByteBuffer] at the given index.
+     * @param at The index to read the [Short] from.
+     */
+    private fun ByteBuffer.getLeShort(at: Int) =
+        get(at + 1).toInt().shl(8).or(get(at).toInt().and(0xFF)).toShort()
+
+    /**
+     * Always write a little-endian [Short] at the end of the [ByteBuffer].
+     * @param short The [Short] to write.
+     */
+    private fun ByteBuffer.putLeShort(short: Short) {
+        put(short.toByte())
+        put(short.toInt().shr(8).toByte())
+    }
+
     /**
      * The resolved ReplayGain adjustment for a file.
      * @param track The track adjustment (in dB), or 0 if it is not present.

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

@@ -238,6 +238,8 @@ class PlaybackStateManager private constructor() {
         when (queue.playNext(songs)) {
             Queue.ChangeResult.MAPPING -> notifyQueueChanged(Queue.ChangeResult.MAPPING)
             Queue.ChangeResult.SONG -> {
+                // Enqueueing actually started a new playback session from all songs.
+                parent = null
                 internalPlayer.loadSong(queue.currentSong, true)
                 notifyNewPlayback()
             }
@@ -261,6 +263,8 @@ class PlaybackStateManager private constructor() {
         when (queue.addToQueue(songs)) {
             Queue.ChangeResult.MAPPING -> notifyQueueChanged(Queue.ChangeResult.MAPPING)
             Queue.ChangeResult.SONG -> {
+                // Enqueueing actually started a new playback session from all songs.
+                parent = null
                 internalPlayer.loadSong(queue.currentSong, true)
                 notifyNewPlayback()
             }

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

@@ -102,7 +102,7 @@ class Queue {
 
             // Since we are re-shuffling existing songs, we use the previous mapping size
             // instead of the total queue size.
-            shuffledMapping = MutableList(orderedMapping.size) { it }.apply { shuffle() }
+            shuffledMapping = orderedMapping.shuffled().toMutableList()
             shuffledMapping.add(0, shuffledMapping.removeAt(shuffledMapping.indexOf(trueIndex)))
             index = 0
         } else if (shuffledMapping.isNotEmpty()) {
@@ -130,11 +130,11 @@ class Queue {
             // Add the new songs in front of the current index in the shuffled mapping and in front
             // of the analogous list song in the ordered mapping.
             val orderedIndex = orderedMapping.indexOf(shuffledMapping[index])
-            orderedMapping.addAll(orderedIndex, heapIndices)
-            shuffledMapping.addAll(index, heapIndices)
+            orderedMapping.addAll(orderedIndex + 1, heapIndices)
+            shuffledMapping.addAll(index + 1, heapIndices)
         } else {
             // Add the new song in front of the current index in the ordered mapping.
-            orderedMapping.addAll(index, heapIndices)
+            orderedMapping.addAll(index + 1, heapIndices)
         }
         return ChangeResult.MAPPING
     }
@@ -207,7 +207,7 @@ class Queue {
             orderedMapping.removeAt(orderedMapping.indexOf(shuffledMapping[at]))
             shuffledMapping.removeAt(at)
         } else {
-            // Remove the spe
+            // Remove the specified index in the shuffled mapping
             orderedMapping.removeAt(at)
         }