playlist: add runtime boilerplate

Add the boilerplate code for the playlist system.

Any functionality is runtime only and is not integrated in-app. Plan is
to build the UI scaffold first followed by the backing playlist.

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

@@ -144,9 +144,11 @@ interface Indexer {
          *
          * @param result The outcome of the music loading process.
          */
-        data class Complete(val result: Result<Library>) : State()
+        data class Complete(val result: Result<Response>) : State()
     }
 
+    data class Response(val result: Library, val playlists: List<Playlist>)
+
     /**
      * Represents the current progress of the music loader. Usually encapsulated in a [State].
      *
@@ -237,7 +239,7 @@ constructor(
     private val mediaStoreExtractor: MediaStoreExtractor,
     private val tagExtractor: TagExtractor
 ) : Indexer {
-    @Volatile private var lastResponse: Result<Library>? = null
+    @Volatile private var lastResponse: Result<Indexer.Response>? = null
     @Volatile private var indexingState: Indexer.Indexing? = null
     @Volatile private var controller: Indexer.Controller? = null
     @Volatile private var listener: Indexer.Listener? = null
@@ -303,11 +305,11 @@ constructor(
             val result =
                 try {
                     val start = System.currentTimeMillis()
-                    val library = indexImpl(context, withCache, this)
+                    val response = indexImpl(context, withCache, this)
                     logD(
                         "Music indexing completed successfully in " +
                             "${System.currentTimeMillis() - start}ms")
-                    Result.success(library)
+                    Result.success(response)
                 } catch (e: CancellationException) {
                     // Got cancelled, propagate upwards to top-level co-routine.
                     logD("Loading routine was cancelled")
@@ -337,7 +339,7 @@ constructor(
         context: Context,
         withCache: Boolean,
         scope: CoroutineScope
-    ): Library {
+    ): Indexer.Response {
         if (ContextCompat.checkSelfPermission(context, Indexer.PERMISSION_READ_AUDIO) ==
             PackageManager.PERMISSION_DENIED) {
             logE("Permission check failed")
@@ -395,7 +397,7 @@ constructor(
         if (cache == null || cache.invalidated) {
             cacheRepository.writeCache(rawSongs)
         }
-        return libraryJob.await()
+        return Indexer.Response(libraryJob.await(), listOf())
     }
 
     /**
@@ -426,7 +428,7 @@ constructor(
      * @param result The new [Result] to emit, representing the outcome of the music loading
      *   process.
      */
-    private suspend fun emitCompletion(result: Result<Library>) {
+    private suspend fun emitCompletion(result: Result<Indexer.Response>) {
         yield()
         // Swap to the Main thread so that downstream callbacks don't crash from being on
         // a background thread. Does not occur in emitIndexing due to efficiency reasons.

app/src/main/java/org/oxycblt/auxio/playback/persist/PersistenceDatabase.kt

@@ -40,7 +40,7 @@ import org.oxycblt.auxio.playback.state.RepeatMode
     entities = [PlaybackState::class, QueueHeapItem::class, QueueMappingItem::class],
     version = 27,
     exportSchema = false)
-@TypeConverters(PersistenceDatabase.Converters::class)
+@TypeConverters(Music.UID.Converter::class)
 abstract class PersistenceDatabase : RoomDatabase() {
     /**
      * Get the current [PlaybackStateDao].

app/src/main/java/org/oxycblt/auxio/playlist/Playlist.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ * Playlist.kt is part of Auxio.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
+package org.oxycblt.auxio.playlist
+
+import java.util.UUID
+import org.oxycblt.auxio.music.Song
+
+interface Playlist {
+    val id: UUID
+    val name: String
+    val songs: List<Song>
+}
+

app/src/main/java/org/oxycblt/auxio/playlist/PlaylistModule.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ * PlaylistModule.kt is part of Auxio.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
+package org.oxycblt.auxio.playlist
+
+import dagger.Binds
+import dagger.Module
+import dagger.hilt.InstallIn
+import dagger.hilt.components.SingletonComponent
+
+@Module
+@InstallIn(SingletonComponent::class)
+interface PlaylistModule {
+    @Binds
+    fun playlistRepository(playlistRepositoryImpl: PlaylistRepositoryImpl): PlaylistRepository
+}

app/src/main/java/org/oxycblt/auxio/playlist/PlaylistRepository.kt

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2023 Auxio Project
+ * PlaylistRepository.kt is part of Auxio.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+ 
+package org.oxycblt.auxio.playlist
+
+import java.util.UUID
+import javax.inject.Inject
+import org.oxycblt.auxio.music.Song
+
+interface PlaylistRepository {
+    val playlists: List<Playlist>
+    suspend fun createPlaylist(name: String, songs: List<Song>)
+    suspend fun deletePlaylist(playlist: Playlist)
+    suspend fun addToPlaylist(playlist: Playlist, songs: List<Song>)
+    suspend fun removeFromPlaylist(playlist: Playlist, song: Song)
+    suspend fun rewritePlaylist(playlist: Playlist, songs: List<Song>)
+}
+
+class PlaylistRepositoryImpl @Inject constructor() : PlaylistRepository {
+    private val playlistMap = mutableMapOf<UUID, PlaylistImpl>()
+    override val playlists: List<Playlist>
+        get() = playlistMap.values.toList()
+
+    override suspend fun createPlaylist(name: String, songs: List<Song>) {
+        val uuid = UUID.randomUUID()
+        playlistMap[uuid] = PlaylistImpl(uuid, name, songs)
+    }
+
+    override suspend fun deletePlaylist(playlist: Playlist) {
+        playlistMap.remove(playlist.id)
+    }
+
+    override suspend fun addToPlaylist(playlist: Playlist, songs: List<Song>) {
+        editPlaylist(playlist) {
+            addAll(songs)
+            this
+        }
+    }
+
+    override suspend fun removeFromPlaylist(playlist: Playlist, song: Song) {
+        editPlaylist(playlist) {
+            remove(song)
+            this
+        }
+    }
+
+    override suspend fun rewritePlaylist(playlist: Playlist, songs: List<Song>) {
+        editPlaylist(playlist) { songs }
+    }
+
+    private inline fun editPlaylist(playlist: Playlist, edits: MutableList<Song>.() -> List<Song>) {
+        check(playlistMap.containsKey(playlist.id)) { "Invalid playlist argument provided" }
+        playlistMap[playlist.id] =
+            PlaylistImpl(playlist.id, playlist.name, edits(playlist.songs.toMutableList()))
+    }
+}
+
+private data class PlaylistImpl(
+    override val id: UUID,
+    override val name: String,
+    override val songs: List<Song>
+) : Playlist