music: add basic multi-genre support [#201]

Add basic support for multiple genres.

This is sort of the test run for full multi-artist support, allowing me
to rework my abstractions to handle the presence of multiple parents.

This is nowhere near complete. For example, there is currently a stopgap
measure in the playback system that basically breaks genre playback.
It's a start though.

app/src/main/java/org/oxycblt/auxio/detail/recycler/ArtistDetailAdapter.kt

@@ -27,6 +27,7 @@ import org.oxycblt.auxio.databinding.ItemParentBinding
 import org.oxycblt.auxio.databinding.ItemSongBinding
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.music.Artist
+import org.oxycblt.auxio.music.Genre
 import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.music.resolveYear
 import org.oxycblt.auxio.ui.recycler.ArtistViewHolder
@@ -111,12 +112,15 @@ private class ArtistDetailViewHolder private constructor(private val binding: It
 
         // Get the genre that corresponds to the most songs in this artist, which would be
         // the most "Prominent" genre.
+        var genresByAmount = mutableMapOf<Genre, Int>()
+        for (song in item.songs) {
+            for (genre in song.genres) {
+                genresByAmount[genre] = genresByAmount[genre]?.inc() ?: 1
+            }
+        }
+
         binding.detailSubhead.text =
-            item.songs
-                .groupBy { it.genre.resolveName(binding.context) }
-                .entries
-                .maxByOrNull { it.value.size }
-                ?.key
+            genresByAmount.maxByOrNull { it.value }?.key?.resolveName(binding.context)
                 ?: binding.context.getString(R.string.def_genre)
 
         binding.detailInfo.text =

app/src/main/java/org/oxycblt/auxio/music/Music.kt

@@ -123,10 +123,10 @@ data class Song(private val raw: Raw) : Music() {
     val album: Album
         get() = unlikelyToBeNull(_album)
 
-    private var _genre: Genre? = null
+    private var _genres: MutableList<Genre> = mutableListOf()
     /** The genre of this song. Will be an "unknown genre" if the song does not have any. */
-    val genre: Genre
-        get() = unlikelyToBeNull(_genre)
+    val genres: List<Genre>
+        get() = _genres
 
     /**
      * The raw artist name for this song in particular. First uses the artist tag, and then falls
@@ -149,14 +149,14 @@ data class Song(private val raw: Raw) : Music() {
             raw.albumName to
             raw.artistName to
             raw.albumArtistName to
-            raw.genreName to
+            raw.genreNames to
             track to
             disc to
             durationMs
 
     val _rawAlbum: Album.Raw
 
-    val _rawGenre = Genre.Raw(raw.genreName)
+    val _rawGenres = raw.genreNames?.map { Genre.Raw(it) } ?: listOf(Genre.Raw(null))
 
     val _isMissingAlbum: Boolean
         get() = _album == null
@@ -165,14 +165,14 @@ data class Song(private val raw: Raw) : Music() {
         get() = _album?._isMissingArtist ?: true
 
     val _isMissingGenre: Boolean
-        get() = _genre == null
+        get() = _genres.isEmpty()
 
     fun _link(album: Album) {
         _album = album
     }
 
     fun _link(genre: Genre) {
-        _genre = genre
+        _genres.add(genre)
     }
 
     init {
@@ -220,7 +220,7 @@ data class Song(private val raw: Raw) : Music() {
         var artistSortName: String? = null,
         var albumArtistName: String? = null,
         var albumArtistSortName: String? = null,
-        var genreName: String? = null
+        var genreNames: List<String>? = null
     )
 }
 
@@ -358,7 +358,16 @@ data class Genre(private val raw: Raw, override val songs: List<Song>) : MusicPa
     val durationMs = songs.sumOf { it.durationMs }
 
     data class Raw(val name: String?) {
-        val groupingId: Long = name.toMusicId()
+        override fun equals(other: Any?): Boolean {
+            if (other !is Raw) return false
+            return when {
+                name != null && other.name != null -> name.equals(other.name, true)
+                name == null && other.name == null -> true
+                else -> false
+            }
+        }
+
+        override fun hashCode() = name?.lowercase().hashCode()
     }
 }
 
@@ -370,7 +379,7 @@ private fun String?.toMusicId(): Long {
 
     var result = 0L
     for (ch in lowercase()) {
-        result = 31 * result + ch.code
+        result = 31 * result + ch.lowercaseChar().code
     }
     return result
 }

app/src/main/java/org/oxycblt/auxio/music/MusicUtil.kt

@@ -110,7 +110,8 @@ fun List<String>.parseReleaseType() = ReleaseType.parse(this)
  * Decodes the genre name from an ID3(v2) constant. See [GENRE_TABLE] for the genre constant map
  * that Auxio uses.
  */
-fun String.parseId3GenreName() = parseId3v1Genre() ?: parseId3v2Genre() ?: this
+fun String.parseId3GenreName() =
+    parseId3v1Genre()?.let { listOf(it) } ?: parseId3v2Genre() ?: listOf(this)
 
 private fun String.parseId3v1Genre(): String? =
     when {
@@ -126,7 +127,7 @@ private fun String.parseId3v1Genre(): String? =
         else -> null
     }
 
-private fun String.parseId3v2Genre(): String? {
+private fun String.parseId3v2Genre(): List<String>? {
     val groups = (GENRE_RE.matchEntire(this) ?: return null).groupValues
     val genres = mutableSetOf<String>()
 
@@ -155,7 +156,7 @@ private fun String.parseId3v2Genre(): String? {
         }
     }
 
-    return genres.joinToString(separator = ", ").ifEmpty { null }
+    return genres.toList()
 }
 
 /** Regex that implements matching for ID3v2's genre format. */

app/src/main/java/org/oxycblt/auxio/music/system/ExoPlayerBackend.kt

@@ -50,7 +50,7 @@ import org.oxycblt.auxio.util.logW
  * @author OxygenCobalt
  */
 class ExoPlayerBackend(private val inner: MediaStoreBackend) : Indexer.Backend {
-    private val runningTasks: Array<Task?> = arrayOfNulls(TASK_CAPACITY)
+    private val taskPool: Array<Task?> = arrayOfNulls(TASK_CAPACITY)
 
     // No need to implement our own query logic, as this backend is still reliant on
     // MediaStore.
@@ -78,19 +78,19 @@ class ExoPlayerBackend(private val inner: MediaStoreBackend) : Indexer.Backend {
             // executor and thus will crash the app if an error occurs instead of bubbling
             // back up to Indexer.
             spin@ while (true) {
-                for (i in runningTasks.indices) {
-                    val task = runningTasks[i]
+                for (i in taskPool.indices) {
+                    val task = taskPool[i]
 
                     if (task != null) {
                         val song = task.get()
                         if (song != null) {
                             songs.add(song)
                             emitIndexing(Indexer.Indexing.Songs(songs.size, total))
-                            runningTasks[i] = Task(context, raw)
+                            taskPool[i] = Task(context, raw)
                             break@spin
                         }
                     } else {
-                        runningTasks[i] = Task(context, raw)
+                        taskPool[i] = Task(context, raw)
                         break@spin
                     }
                 }
@@ -99,14 +99,14 @@ class ExoPlayerBackend(private val inner: MediaStoreBackend) : Indexer.Backend {
 
         spin@ while (true) {
             // Spin until all of the remaining tasks are complete.
-            for (i in runningTasks.indices) {
-                val task = runningTasks[i]
+            for (i in taskPool.indices) {
+                val task = taskPool[i]
 
                 if (task != null) {
                     val song = task.get() ?: continue@spin
                     songs.add(song)
                     emitIndexing(Indexer.Indexing.Songs(songs.size, total))
-                    runningTasks[i] = null
+                    taskPool[i] = null
                 }
             }
 
@@ -249,7 +249,7 @@ class Task(context: Context, private val raw: Song.Raw) {
         tags["TSO2"]?.let { raw.albumArtistSortName = it }
 
         // Genre, with the weird ID3 rules.
-        tags["TCON"]?.let { raw.genreName = it.parseId3GenreName() }
+        tags["TCON"]?.let { raw.genreNames = it.parseId3GenreName() }
 
         // Release type (GRP1 is sometimes used for this, so fall back to it)
         (tags["TXXX:MusicBrainz Album Type"] ?: tags["GRP1"])?.parseReleaseType()?.let {
@@ -313,7 +313,7 @@ class Task(context: Context, private val raw: Song.Raw) {
         tags["ALBUMARTISTSORT"]?.let { raw.albumArtistSortName = it.joinToString() }
 
         // Genre, no ID3 rules here
-        tags["GENRE"]?.let { raw.genreName = it.joinToString() }
+        tags["GENRE"]?.let { raw.genreNames = it }
 
         // Release type
         tags["RELEASETYPE"]?.parseReleaseType()?.let { raw.albumReleaseType = it }

app/src/main/java/org/oxycblt/auxio/music/system/Indexer.kt

@@ -332,12 +332,15 @@ class Indexer {
      */
     private fun buildGenres(songs: List<Song>): List<Genre> {
         val genres = mutableListOf<Genre>()
-        val songsByGenre = songs.groupBy { it._rawGenre.groupingId }
+        val songsByGenre = mutableMapOf<Genre.Raw, MutableList<Song>>()
+        for (song in songs) {
+            for (rawGenre in song._rawGenres) {
+                songsByGenre.getOrPut(rawGenre) { mutableListOf() }.add(song)
+            }
+        }
 
         for (entry in songsByGenre) {
-            // The first song fill suffice for template metadata.
-            val templateSong = entry.value[0]
-            genres.add(Genre(templateSong._rawGenre, songs = entry.value))
+            genres.add(Genre(entry.key, songs = entry.value))
         }
 
         logD("Successfully built ${genres.size} genres")

app/src/main/java/org/oxycblt/auxio/music/system/MediaStoreBackend.kt

@@ -201,7 +201,7 @@ abstract class MediaStoreBackend : Indexer.Backend {
                         val songId = cursor.getLong(songIdIndex)
                         rawSongs
                             .find { it.mediaStoreId == songId }
-                            ?.let { song -> song.genreName = name }
+                            ?.let { song -> song.genreNames = name }
 
                         if (cursor.position % 50 == 0) {
                             // Only check for a cancellation every 50 songs or so (~20ms).

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

@@ -162,7 +162,8 @@ class PlaybackStateManager private constructor() {
                 PlaybackMode.ALL_SONGS -> null
                 PlaybackMode.IN_ALBUM -> song.album
                 PlaybackMode.IN_ARTIST -> song.album.artist
-                PlaybackMode.IN_GENRE -> song.genre
+                PlaybackMode.IN_GENRE ->
+                    song.genres.maxBy { it.songs.size } // TODO: Stopgap measure until I can rework this and add selection
             }
 
         applyNewQueue(library, settings, settings.keepShuffle && isShuffled, song)

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

@@ -160,7 +160,9 @@ class MediaSessionComponent(
                 .putText(MediaMetadataCompat.METADATA_KEY_AUTHOR, artist)
                 .putText(MediaMetadataCompat.METADATA_KEY_COMPOSER, artist)
                 .putText(MediaMetadataCompat.METADATA_KEY_WRITER, artist)
-                .putText(MediaMetadataCompat.METADATA_KEY_GENRE, song.genre.resolveName(context))
+                .putText(
+                    MediaMetadataCompat.METADATA_KEY_GENRE,
+                    song.genres.joinToString { it.resolveName(context) })
                 .putText(
                     METADATA_KEY_PARENT,
                     parent?.resolveName(context) ?: context.getString(R.string.lbl_all_songs))