address fourth review: reset the saved position per track and serialize cursor writes

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

@@ -10,6 +10,8 @@ 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 kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import java.util.concurrent.atomic.AtomicLong
 
 const val QUEUE_CHUNK = 60
@@ -71,6 +73,8 @@ class QueueRepository(
     @Volatile
     private var cachedFlatVersion = -1L
 
+    private val cursorMutex = Mutex()
+
     fun playlistEntry(
         sourceId: Long,
         playlistId: String,
@@ -94,7 +98,7 @@ class QueueRepository(
     ) {
         write(entries)
         setShuffle(shuffleOrder != null, shuffleOrder)
-        dao.setCursor(cursorRow().copy(queuePosition = 0))
+        cursorMutex.withLock { dao.setCursor(cursorRow().copy(queuePosition = 0, positionMs = 0)) }
     }
 
     suspend fun snapshot(): QueueSnapshot {
@@ -124,6 +128,7 @@ class QueueRepository(
         order: LongArray?,
     ) {
         val seed = if (enabled && order != null) System.nanoTime() else 0L
+        cursorMutex.withLock {
             db.useWriterConnection { transactor ->
                 transactor.immediateTransaction {
                     dao.clearShuffleOrder()
@@ -133,6 +138,7 @@ class QueueRepository(
                     dao.setCursor(cursorRow().copy(shuffleEnabled = enabled, shuffleSeed = seed))
                 }
             }
+        }
         cachedShuffleSeed = 0
         cachedShuffleOrder = null
     }
@@ -142,7 +148,7 @@ class QueueRepository(
         queueVersion.incrementAndGet()
     }
 
-    suspend fun setRepeat(mode: Int) = dao.setCursor(cursorRow().copy(repeatMode = mode))
+    suspend fun setRepeat(mode: Int) = cursorMutex.withLock { dao.setCursor(cursorRow().copy(repeatMode = mode)) }
 
     private suspend fun loadShuffleOrder(
         seed: Long,
@@ -272,9 +278,16 @@ class QueueRepository(
 
     suspend fun cursorPositionMs(): Long = dao.cursor()?.positionMs ?: 0
 
-    suspend fun setPosition(positionMs: Long) = dao.setCursor(cursorRow().copy(positionMs = positionMs.coerceAtLeast(0)))
+    suspend fun setPosition(positionMs: Long) =
+        cursorMutex.withLock {
+            dao.setCursor(cursorRow().copy(positionMs = positionMs.coerceAtLeast(0)))
+        }
 
-    suspend fun setCursor(position: Long) = dao.setCursor(cursorRow().copy(queuePosition = position))
+    suspend fun setCursor(position: Long) =
+        cursorMutex.withLock {
+            val row = cursorRow()
+            dao.setCursor(row.copy(queuePosition = position, positionMs = if (row.queuePosition == position) row.positionMs else 0))
+        }
 
     private suspend fun cursorRow(): PlaybackCursor = dao.cursor() ?: PlaybackCursor(queuePosition = 0)
 

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

@@ -234,6 +234,7 @@ class PlaybackController(
             val order = withContext(Dispatchers.Default) { shuffledOrder(snap.size, start) }
             queueRepository.setShuffle(true, order)
             shuffleEnabled = true
+            queueSourceId = entry.sourceId
             queueRepository.setCursor(0)
             snap = queueRepository.snapshot()
             this@PlaybackController.snapshot = snap

app/src/main/kotlin/com/subtracks/ui/playback/QueueScreen.kt

@@ -116,7 +116,7 @@ class QueueViewModel(
                     rows.addAll(queueRepository.range(snapshot, start, end).map(::newRow))
                     first = rows.firstOrNull()?.position ?: 0
                     last = rows.lastOrNull()?.position ?: -1
-                    initialIndex = (cursor - first).toInt().coerceAtLeast(0)
+                    initialIndex = rows.indexOfFirst { it.position == cursor }.coerceAtLeast(0)
                 }
                 ready = true
                 generation++

app/src/test/kotlin/com/subtracks/playback/PlaybackControllerTest.kt

@@ -932,6 +932,26 @@ class PlaybackControllerTest {
         restored.close()
     }
 
+    @Test
+    fun changingTrackResetsTheSavedPosition() {
+        seedAlbum(3, sourceId = 1)
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+
+        runBlocking { queues.setPosition(60_000L) }
+
+        controller.next()
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        assertEquals(0L, runBlocking { queues.cursorPositionMs() })
+    }
+
     private fun seedAlbum(
         count: Int,
         sourceId: Long,