add a one-step undo and harden queue edits

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

@@ -42,7 +42,7 @@ class QueuePagingSourceTest {
         runTest {
             seedSongs(130)
             repository.replace(listOf(repository.songsEntry(1)))
-            val source = repository.pagingSource()
+            val source = repository.pagingSource(initialPosition = 0)
 
             val first = load(source, key = null)
             assertEquals((0L until 60L).toList(), first.data.map { it.position })
@@ -60,10 +60,24 @@ class QueuePagingSourceTest {
             assertEquals(1L, third.prevKey)
         }
 
+    @Test
+    fun theFirstPageStartsAtTheInitialPosition() =
+        runTest {
+            seedSongs(130)
+            repository.replace(listOf(repository.songsEntry(1)))
+            val source = repository.pagingSource(initialPosition = 100)
+
+            val first = load(source, key = null)
+
+            assertEquals((60L until 120L).toList(), first.data.map { it.position })
+            assertEquals(2L, first.nextKey)
+            assertEquals(0L, first.prevKey)
+        }
+
     @Test
     fun anEmptyQueueLoadsNothing() =
         runTest {
-            val result = load(repository.pagingSource(), key = null)
+            val result = load(repository.pagingSource(0), key = null)
 
             assertEquals(emptyList<QueueWindowItem>(), result.data)
             assertEquals(null, result.nextKey)

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

@@ -15,6 +15,8 @@ import com.subtracks.data.model.Source
 import kotlinx.coroutines.test.runTest
 import org.junit.After
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
 import org.junit.Before
 import org.junit.Test
 import org.junit.runner.RunWith
@@ -299,6 +301,17 @@ class QueueRepositoryTest {
             assertEquals(listOf("s2", "s3", "s4", "s1"), resolveAll(repository.snapshot()))
         }
 
+    @Test
+    fun movingFromOutsideTheQueueChangesNothing() =
+        runTest {
+            seedLibrary()
+            repository.snapshotAfter(listOf(repository.albumEntry(1, "al1")))
+
+            assertFalse(repository.move(from = 5, to = 0))
+            assertTrue(repository.move(from = 0, to = 2))
+            assertEquals(listOf("s2", "s3", "s1"), resolveAll(repository.snapshot()))
+        }
+
     private suspend fun QueueRepository.snapshotAfter(entries: List<QueueEntry>): QueueSnapshot {
         replace(entries)
         return snapshot()

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

@@ -370,7 +370,7 @@ class PlaybackControllerTest {
         }
 
         assertEquals(0L, controller.state.value.position)
-        assertTrue(handle.operations.contains("removeAt(0)"))
+        assertTrue(handle.operations.any { it.startsWith("setWindow") })
         assertFalse(controller.state.value.hasPrevious)
     }
 
@@ -437,6 +437,79 @@ class PlaybackControllerTest {
         )
     }
 
+    @Test
+    fun undoRestoresARemovedTrack() {
+        seedAlbum(5, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 2)
+        await {
+            controller.state.value.item
+                ?.id == "s3"
+        }
+
+        runBlocking { controller.removeAt(3) }
+        await { handle.itemCount == 4 }
+
+        runBlocking { controller.undo() }
+        await { handle.itemCount == 5 }
+
+        assertEquals(listOf("s1", "s2", "s3", "s4", "s5"), handle.items.map { it.id })
+        assertEquals(
+            "s3",
+            controller.state.value.item
+                ?.id,
+        )
+        assertEquals(2L, controller.state.value.position)
+    }
+
+    @Test
+    fun undoRestoresAReorderedQueue() {
+        seedAlbum(4, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+
+        runBlocking { controller.move(0, 2) }
+        await { handle.items.map { it.id } == listOf("s2", "s3", "s1", "s4") }
+
+        runBlocking { controller.undo() }
+        await { handle.items.map { it.id } == listOf("s1", "s2", "s3", "s4") }
+
+        assertEquals(
+            "s1",
+            controller.state.value.item
+                ?.id,
+        )
+        assertEquals(0L, controller.state.value.position)
+    }
+
+    @Test
+    fun startingANewQueueClearsTheUndo() {
+        seedAlbum(3, sourceId = 1)
+
+        controller.playAlbum(1, "al1", 0)
+        await {
+            controller.state.value.item
+                ?.id == "s1"
+        }
+
+        runBlocking { controller.removeAt(1) }
+        await { handle.itemCount == 2 }
+
+        controller.playAlbum(1, "al1", 2)
+        await {
+            controller.state.value.item
+                ?.id == "s3"
+        }
+
+        runBlocking { controller.undo() }
+
+        assertEquals(listOf("s1", "s2", "s3"), handle.items.map { it.id })
+    }
+
     private fun seedAlbum(
         count: Int,
         sourceId: Long,

app/src/test/kotlin/com/subtracks/ui/AppScreenshotTest.kt

@@ -237,6 +237,7 @@ class AppScreenshotTest {
                     onPlay = {},
                     onRemove = {},
                     onMove = { _, _ -> },
+                    onUndo = {},
                     modifier = Modifier.fillMaxSize(),
                 )
             }