fix the queue paging refresh key and drag edge detection

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

@@ -9,19 +9,27 @@ class QueuePagingSource(
     private val repository: QueueRepository,
     private val initialPosition: Long,
 ) : PagingSource<Long, QueueWindowItem>() {
-    override fun getRefreshKey(state: PagingState<Long, QueueWindowItem>): Long? =
+    override fun getRefreshKey(state: PagingState<Long, QueueWindowItem>): Long? {
-        state.anchorPosition?.let { (it / QUEUE_PAGE_SIZE).toLong() }
+        val anchor = state.anchorPosition ?: return null
+        val first =
+            state.pages
+                .firstOrNull()
+                ?.data
+                ?.firstOrNull()
+                ?.position ?: return null
+        return (first + anchor) / QUEUE_PAGE_SIZE
+    }
 
     override suspend fun load(params: LoadParams<Long>): LoadResult<Long, QueueWindowItem> {
         val snapshot = repository.snapshot()
-        val page = params.key ?: (initialPosition.coerceAtLeast(0) / QUEUE_PAGE_SIZE)
+        if (snapshot.size == 0L) return LoadResult.Page(emptyList(), null, null)
+        val lastPage = (snapshot.size - 1) / QUEUE_PAGE_SIZE
+        val page = (params.key ?: (initialPosition.coerceAtLeast(0) / QUEUE_PAGE_SIZE)).coerceIn(0, lastPage)
         val offset = page * QUEUE_PAGE_SIZE
-        val previousKey = if (page > 0) page - 1 else null
-        if (offset >= snapshot.size) return LoadResult.Page(emptyList(), previousKey, null)
         val end = (offset + params.loadSize).coerceAtMost(snapshot.size)
         return LoadResult.Page(
             data = repository.range(snapshot, offset, end - 1),
-            prevKey = previousKey,
+            prevKey = if (page > 0) page - 1 else null,
             nextKey = if (end < snapshot.size) end / QUEUE_PAGE_SIZE else null,
         )
     }

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

@@ -49,11 +49,13 @@ data class PlaybackState(
 private sealed interface QueueUndo {
     val entries: List<QueueEntry>
     val cursor: Long
+    val current: Long?
 }
 
 private data class RemovedUndo(
     override val entries: List<QueueEntry>,
     override val cursor: Long,
+    override val current: Long,
     val position: Long,
     val item: QueueItem?,
 ) : QueueUndo
@@ -61,6 +63,7 @@ private data class RemovedUndo(
 private data class MovedUndo(
     override val entries: List<QueueEntry>,
     override val cursor: Long,
+    override val current: Long,
     val from: Long,
     val to: Long,
 ) : QueueUndo
@@ -68,7 +71,9 @@ private data class MovedUndo(
 private data class ReloadUndo(
     override val entries: List<QueueEntry>,
     override val cursor: Long,
-) : QueueUndo
+) : QueueUndo {
+    override val current: Long? = null
+}
 
 class PlaybackController(
     private val sourceRepository: SourceRepository,
@@ -195,7 +200,7 @@ class PlaybackController(
                 if (removed == null) {
                     ReloadUndo(entries, cursor)
                 } else {
-                    RemovedUndo(entries, cursor, position, removed)
+                    RemovedUndo(entries, cursor, target, position, removed)
                 }
             when {
                 position == current -> {
@@ -242,7 +247,7 @@ class PlaybackController(
         val inWindow = from in windowStart..windowEnd && to in windowStart..windowEnd
         lastEdit =
             if (inWindow) {
-                MovedUndo(entries, cursor, from, to)
+                MovedUndo(entries, cursor, target, from, to)
             } else {
                 ReloadUndo(entries, cursor)
             }
@@ -275,7 +280,11 @@ class PlaybackController(
             val target = undo.cursor.coerceIn(0, restored.size - 1)
             val restoredId = queueRepository.itemAt(restored, target)?.song?.id
             windowJob?.cancel()
-            val canMirror = player.currentItem?.id != null && player.currentItem?.id == restoredId
+            val canMirror =
+                undo.current != null &&
+                    player.currentItem?.id != null &&
+                    player.currentItem?.id == restoredId &&
+                    currentPosition() == undo.current
             val mirrored =
                 when {
                     !canMirror -> {

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

@@ -180,10 +180,11 @@ fun QueueScreen(
             val from = dragging ?: break
             val info = listState.layoutInfo.visibleItemsInfo.firstOrNull { items.peek(it.index)?.position == from }
             if (info != null) {
+                val top = info.offset + dragOffset
                 val edge =
                     when {
-                        info.offset < listState.layoutInfo.viewportStartOffset + threshold -> -step
+                        top < listState.layoutInfo.viewportStartOffset + threshold -> -step
-                        info.offset + info.size > listState.layoutInfo.viewportEndOffset - threshold -> step
+                        top + info.size > listState.layoutInfo.viewportEndOffset - threshold -> step
                         else -> 0f
                     }
                 if (edge != 0f) {

app/src/test/kotlin/com/subtracks/data/repo/QueuePagingSourceTest.kt

@@ -1,13 +1,16 @@
 package com.subtracks.data.repo
 
 import android.content.Context
+import androidx.paging.PagingConfig
 import androidx.paging.PagingSource
+import androidx.paging.PagingState
 import androidx.room3.Room
 import androidx.sqlite.driver.bundled.BundledSQLiteDriver
 import androidx.test.core.app.ApplicationProvider
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.subtracks.data.db.SubtracksDatabase
 import com.subtracks.data.model.Song
+import com.subtracks.data.model.SongListItem
 import com.subtracks.data.model.Source
 import kotlinx.coroutines.test.runTest
 import org.junit.After
@@ -74,6 +77,21 @@ class QueuePagingSourceTest {
             assertEquals(0L, first.prevKey)
         }
 
+    @Test
+    fun theRefreshKeyUsesTheLoadedPositions() =
+        runTest {
+            val source = repository.pagingSource(initialPosition = 100)
+            val state =
+                PagingState(
+                    pages = listOf(PagingSource.LoadResult.Page(listOf(itemAt(60)), prevKey = 0L, nextKey = 2L)),
+                    anchorPosition = 5,
+                    config = PagingConfig(pageSize = QUEUE_PAGE_SIZE, enablePlaceholders = false),
+                    leadingPlaceholderCount = 0,
+                )
+
+            assertEquals(1L, source.getRefreshKey(state))
+        }
+
     @Test
     fun anEmptyQueueLoadsNothing() =
         runTest {
@@ -84,6 +102,29 @@ class QueuePagingSourceTest {
             assertEquals(null, result.prevKey)
         }
 
+    private fun itemAt(position: Long) =
+        QueueWindowItem(
+            position,
+            SongListItem(
+                song =
+                    Song(
+                        sourceId = 1,
+                        id = "s$position",
+                        albumId = "al1",
+                        artistId = "ar1",
+                        title = "Song $position",
+                        album = "Album",
+                        artist = "Artist",
+                        duration = 100,
+                        track = position,
+                        disc = 1,
+                        starred = null,
+                        genre = null,
+                    ),
+                coverArt = null,
+            ),
+        )
+
     private suspend fun load(
         source: PagingSource<Long, QueueWindowItem>,
         key: Long?,