address third review: rebuild the window when the shuffle is dropped, atomic queue version

app/src/main/kotlin/com/subtracks/data/repo/QueueRepository.kt

@@ -10,6 +10,7 @@ import com.subtracks.data.model.QueueEntry
 import com.subtracks.data.model.QueueKind
 import com.subtracks.data.model.ShuffleOrder
 import com.subtracks.data.model.SongListItem
+import java.util.concurrent.atomic.AtomicLong
 
 const val QUEUE_CHUNK = 60
 
@@ -62,8 +63,7 @@ class QueueRepository(
     @Volatile
     private var cachedShuffleOrder: LongArray? = null
 
-    @Volatile
-    private var queueVersion = 0L
+    private val queueVersion = AtomicLong()
 
     @Volatile
     private var cachedFlatIds: List<String>? = null
@@ -98,6 +98,7 @@ class QueueRepository(
     }
 
     suspend fun snapshot(): QueueSnapshot {
+        val version = queueVersion.get()
         val loaded =
             db.useReaderConnection { transactor ->
                 transactor.deferredTransaction {
@@ -110,7 +111,7 @@ class QueueRepository(
             }
         val (entries, order, shuffled) = loaded
         val valid = if (shuffled && order == null) null else order
-        return QueueSnapshot(entries, valid, queueVersion)
+        return QueueSnapshot(entries, valid, version)
     }
 
     suspend fun modes(): QueueModes {
@@ -138,7 +139,7 @@ class QueueRepository(
 
     fun invalidateLibraryCache() {
         cachedFlatIds = null
-        queueVersion++
+        queueVersion.incrementAndGet()
     }
 
     suspend fun setRepeat(mode: Int) = dao.setCursor(cursorRow().copy(repeatMode = mode))
@@ -173,6 +174,15 @@ class QueueRepository(
         return rows(entry, entry.offset + offset, 1).firstOrNull()
     }
 
+    suspend fun flatIndexOf(
+        snapshot: QueueSnapshot,
+        songId: String,
+    ): Long? {
+        if (!snapshot.shuffled) return null
+        val index = flatIds(snapshot).indexOf(songId)
+        return if (index >= 0) index.toLong() else null
+    }
+
     suspend fun range(
         snapshot: QueueSnapshot,
         first: Long,
@@ -271,7 +281,7 @@ class QueueRepository(
                 dao.insert(entries.mapIndexed { index, entry -> entry.copy(id = 0, position = index.toLong()) })
             }
         }
-        queueVersion++
+        queueVersion.incrementAndGet()
         cachedFlatIds = null
     }
 

app/src/main/kotlin/com/subtracks/playback/PlaybackController.kt

@@ -398,8 +398,10 @@ class PlaybackController(
     fun previous() {
         val player = player ?: return
         if (player.currentPositionMs > RESTART_THRESHOLD_MS) {
-            player.seekTo(0)
-            refresh()
+            scope.launch {
+                startLock.withLock { player.seekTo(0) }
+                refresh()
+            }
             return
         }
         val snapshot = snapshot ?: return
@@ -657,9 +659,20 @@ class PlaybackController(
 
     private suspend fun shiftWindowLocked(center: Long) {
         val player = player ?: return
+        val previous = snapshot
         val snapshot = readSnapshot()
         this.snapshot = snapshot
         if (snapshot.size == 0L) return
+        if (previous != null && previous.shuffled != snapshot.shuffled) {
+            val currentId = player.currentItem?.id
+            val position =
+                (currentId?.let { queueRepository.flatIndexOf(snapshot, it) } ?: center)
+                    .coerceIn(0, snapshot.size - 1)
+            queueRepository.setCursor(position)
+            rebuildWindow(queueRepository.window(snapshot, position, QUEUE_WINDOW_RADIUS), position)
+            refresh(position)
+            return
+        }
         val target = center.coerceIn(0, snapshot.size - 1)
         val desiredStart = (target - QUEUE_WINDOW_RADIUS).coerceAtLeast(0)
         val desiredEnd = (target + QUEUE_WINDOW_RADIUS).coerceAtMost(snapshot.size - 1)