avoid reloading the window on queue edits; add clear up next

- moves that straddle the player window, and deletes that are not the
  current track, rebuilt the playlist with setWindow, restarting the
  playing track (a pause). They now reuse rebuildWindow, which re-lays
  the window around the playing item without replacing it.
- deleting the currently playing queued track now removes it from the
  player in place so it advances to the next track without a reload.
- the Up next section header has a clear button that drops the whole
  queued block and resumes the context after the anchor.

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

@@ -378,6 +378,10 @@ class QueueRepository(
         return Reanchored(play, true)
     }
 
+    suspend fun clearUpNext() {
+        writeUpNext(emptyList())
+    }
+
     suspend fun removeUpNextAt(
         snapshot: QueueSnapshot,
         index: Long,

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

@@ -346,7 +346,19 @@ class PlaybackController(
                 }
             if (snapshot.upNextSize > 0L || updated.upNextSize > 0L) {
                 queueRepository.setCursor(target)
-                loadWindow(target, autoplay = playing, startPositionMs = if (position == current) 0 else player.currentPositionMs)
+                if (position != current) {
+                    rebuildWindow(queueRepository.window(updated, target, QUEUE_WINDOW_RADIUS), target)
+                    refresh(target)
+                } else if (target - windowStart in 0 until player.itemCount) {
+                    updating = true
+                    player.removeAt((target - windowStart).toInt())
+                    updating = false
+                    windowEnd--
+                    shiftWindowLocked(target)
+                    refresh(target)
+                } else {
+                    loadWindow(target, autoplay = playing)
+                }
                 return@withLock
             }
             when {
@@ -389,7 +401,8 @@ class PlaybackController(
         val entries = snapshot.entries.map { it.entry }
         val upNext = snapshot.upNext.map { it.entry }
         if (!queueRepository.move(snapshot, from, to)) return@withLock
-        this.snapshot = readSnapshot()
+        val updated = readSnapshot()
+        this.snapshot = updated
         val target = movedCursor(current, from, to)
         lastPosition = target
         windowJob?.cancel()
@@ -425,7 +438,7 @@ class PlaybackController(
             }
 
             else -> {
-                loadWindow(target, autoplay = player.playWhenReady, startPositionMs = player.currentPositionMs)
+                rebuildWindow(queueRepository.window(updated, target, QUEUE_WINDOW_RADIUS), target)
             }
         }
         shiftWindowLocked(target)
@@ -567,6 +580,34 @@ class PlaybackController(
             }
         }
 
+    fun clearUpNext() {
+        scope.launch {
+            startLock.withLock {
+                val snapshot = snapshot ?: return@withLock
+                if (snapshot.upNextSize == 0L) return@withLock
+                player ?: return@withLock
+                val current = currentPosition() ?: return@withLock
+                val wasUpNext = snapshot.isUpNext(current)
+                queueRepository.clearUpNext()
+                val updated = readSnapshot()
+                this@PlaybackController.snapshot = updated
+                layoutVersion++
+                windowJob?.cancel()
+                endedHandled = false
+                val contextPlay = if (wasUpNext) snapshot.anchorPlay + 1 else snapshot.contextPlay(current)
+                val target = contextPlay.coerceIn(0, (updated.size - 1).coerceAtLeast(0))
+                queueRepository.setCursor(target)
+                lastPosition = target
+                if (wasUpNext) {
+                    loadWindow(target, autoplay = true)
+                } else {
+                    rebuildWindow(queueRepository.window(updated, target, QUEUE_WINDOW_RADIUS), target)
+                    refresh(target)
+                }
+            }
+        }
+    }
+
     fun previous() {
         val player = player ?: return
         if (player.currentPositionMs > RESTART_THRESHOLD_MS) {

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

@@ -299,6 +299,7 @@ fun QueueRoute(
         currentSongId = playback.item?.id,
         shuffle = playback.shuffle,
         contextTitle = sourceTitle.value,
+        onClearUpNext = controller::clearUpNext,
         coverArt = sourceRepository::coverArt,
         onBack = onBack,
         onPlay = viewModel::play,
@@ -332,6 +333,7 @@ fun QueueScreen(
     generation: Int = 0,
     shuffle: Boolean = false,
     contextTitle: String? = null,
+    onClearUpNext: () -> Unit = {},
 ) {
     val listState = rememberLazyListState()
     val fill = rememberViewportFill(listState)
@@ -403,7 +405,10 @@ fun QueueScreen(
                     rows.forEachIndexed { index, row ->
                         if (index == 0 || rows[index - 1].upNext != row.upNext) {
                             item(key = "header-$index") {
-                                QueueSectionHeader(if (row.upNext) "Up next" else contextTitle ?: "Next up")
+                                QueueSectionHeader(
+                                    label = if (row.upNext) "Up next" else contextTitle ?: "Next up",
+                                    onClear = if (row.upNext) onClearUpNext else null,
+                                )
                             }
                         }
                         val enabled = row.upNext || !shuffle
@@ -471,13 +476,26 @@ fun QueueScreen(
 }
 
 @Composable
-private fun QueueSectionHeader(label: String) {
-    Text(
-        text = label,
-        style = MaterialTheme.typography.labelLarge,
-        color = MaterialTheme.colorScheme.primary,
-        modifier = Modifier.fillMaxWidth().padding(start = 16.dp, top = 16.dp, bottom = 4.dp),
-    )
+private fun QueueSectionHeader(
+    label: String,
+    onClear: (() -> Unit)? = null,
+) {
+    Row(
+        verticalAlignment = Alignment.CenterVertically,
+        modifier = Modifier.fillMaxWidth().padding(start = 16.dp, top = 16.dp, end = 4.dp, bottom = 4.dp),
+    ) {
+        Text(
+            text = label,
+            style = MaterialTheme.typography.labelLarge,
+            color = MaterialTheme.colorScheme.primary,
+            modifier = Modifier.weight(1f),
+        )
+        if (onClear != null) {
+            IconButton(onClick = onClear) {
+                Icon(Icons.Rounded.Close, contentDescription = "Clear up next", modifier = Modifier.size(20.dp))
+            }
+        }
+    }
 }
 
 private fun List<QueueRow>.rowIndexOf(key: Any?): Int {

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

@@ -851,6 +851,81 @@ class PlaybackControllerTest {
         assertFalse(handle.operations.any { it.startsWith("setWindow") })
     }
 
+    @Test
+    fun clearingTheQueueResumesTheContext() {
+        seedAlbum(3, sourceId = 1)
+        seedSong("x1", "al2")
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Song, "x1")
+        controller.next()
+        await {
+            controller.state.value.item
+                ?.id == "x1"
+        }
+
+        controller.clearUpNext()
+        await {
+            controller.state.value.item
+                ?.id == "s2"
+        }
+
+        assertTrue(runBlocking { queues.snapshot().upNext }.isEmpty())
+    }
+
+    @Test
+    fun clearingTheQueueWhileOnTheContextKeepsPlaying() {
+        seedAlbum(3, sourceId = 1)
+        seedSong("x1", "al2")
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Song, "x1")
+        await { runBlocking { controller.upcomingItem()?.id } == "x1" }
+
+        controller.clearUpNext()
+        Thread.sleep(200)
+
+        assertEquals(
+            "s1",
+            controller.state.value.item
+                ?.id,
+        )
+        assertTrue(runBlocking { queues.snapshot().upNext }.isEmpty())
+    }
+
+    @Test
+    fun movingAFarQueuedTrackDoesNotReloadTheWindow() {
+        seedAlbum(3, sourceId = 1)
+        seedAlbumTracks("al2", 60)
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+        controller.addToQueue(1, QueueKind.Album, "al2")
+        await { runBlocking { controller.upcomingItem()?.id } == "al2-b1" }
+
+        handle.operations.clear()
+        runBlocking { controller.move(50, 2) }
+        Thread.sleep(300)
+
+        assertEquals(
+            "s1",
+            controller.state.value.item
+                ?.id,
+        )
+        assertFalse(handle.operations.any { it.startsWith("setWindow") })
+    }
+
     @Test
     fun nextFollowsTheReorderedQueue() {
         seedAlbum(3, sourceId = 1)
@@ -1846,6 +1921,32 @@ class PlaybackControllerTest {
         }
     }
 
+    private fun seedAlbumTracks(
+        albumId: String,
+        count: Int,
+    ) {
+        runBlocking {
+            db.libraryDao().upsertSongs(
+                (1..count).map { track ->
+                    Song(
+                        sourceId = 1,
+                        id = "$albumId-b$track",
+                        albumId = albumId,
+                        artistId = "ar1",
+                        title = "Album $albumId track $track",
+                        album = "Album $albumId",
+                        artist = "Artist",
+                        duration = 100,
+                        track = track.toLong(),
+                        disc = 1,
+                        starred = null,
+                        genre = null,
+                    )
+                },
+            )
+        }
+    }
+
     private fun seedSong(
         id: String,
         albumId: String,