feat: beat annotator

app/src/main/java/at/lockstep/player/LockstepViewModel.kt

@@ -10,6 +10,8 @@ import at.lockstep.jukebox.db.TrackRow
 import at.lockstep.player.data.UserPreferencesRepository
 import at.lockstep.player.data.db.TrackPairingEntity
 import at.lockstep.player.util.AudioUriValidator
+import at.lockstep.player.playback.TrackBoundaryEvent
+import at.lockstep.player.util.BeatAnnotationStorage
 import at.lockstep.player.util.FolderMp3Scanner
 import at.lockstep.player.util.Mp3EmbeddedMetadata
 import at.lockstep.player.util.Mp3FolderCandidate
@@ -56,6 +58,19 @@ class LockstepViewModel(
             null,
         )
 
+    val annotationMode: StateFlow<Boolean> =
+        prefs.annotationMode.stateIn(
+            viewModelScope,
+            SharingStarted.Eagerly,
+            false,
+        )
+
+    fun setAnnotationMode(enabled: Boolean) {
+        viewModelScope.launch {
+            prefs.setAnnotationMode(enabled)
+        }
+    }
+
     private val context get() = getApplication<Application>()
 
     /**
@@ -120,6 +135,45 @@ class LockstepViewModel(
 
     suspend fun hasPairedTracks(playlistId: String): Boolean = pairingDao.countPaired(playlistId) > 0
 
+    suspend fun getPlaylistDisplayName(playlistId: String): String =
+        withContext(Dispatchers.IO) {
+            app.playlistRepository.getPlaylists()
+                .find { it.id == playlistId }
+                ?.name
+                ?.trim()
+                .orEmpty()
+                .ifBlank { "playlist" }
+        }
+
+    /**
+     * Writes one JSON file under app files dir ([BeatAnnotationStorage]) for the track described
+     * by [event]. Skips when [beatTimesMs] is empty.
+     */
+    fun persistBeatAnnotation(
+        playlistId: String,
+        playlistDisplayName: String,
+        event: TrackBoundaryEvent,
+        beatTimesMs: List<Long>,
+    ) {
+        if (beatTimesMs.isEmpty()) {
+            return
+        }
+        viewModelScope.launch(Dispatchers.IO) {
+            val pairing = pairingDao.findForTrack(playlistId, event.trackId)
+            val docId = BeatAnnotationStorage.mp3DocumentContentId(pairing?.localUri)
+            val contentId = docId.ifBlank { event.trackId }
+            BeatAnnotationStorage.writeAnnotationsFile(
+                context = getApplication(),
+                playlistDisplayName = playlistDisplayName,
+                trackQueueIndex0Based = event.queueIndex,
+                contentId = contentId,
+                title = event.title,
+                artist = event.artist,
+                beatTimesMs = beatTimesMs,
+            )
+        }
+    }
+
     suspend fun syncJukeboxIfToken(): String? {
         val token = spotifyAccessToken.value
         if (token.isNullOrBlank()) {