Implement incremental sync and offline recovery

apps/apple/VelodyiPhone/Sources/iPhoneLibraryViewModel.swift

@@ -476,13 +476,15 @@ final class iPhoneLibraryViewModel {
             }
         )
         let store = Self.makeRemoteLibraryStore()
+        let syncCursorStore = Self.makeRemoteLibrarySyncCursorStore()
         let downloadStateStore = Self.makeRemoteTrackDownloadStateStore()
         let audioFileStore = Self.makeOfflineAudioFileStore()
         let artworkStore = Self.makeArtworkStore()
         let favoriteTrackStore = Self.makeFavoriteTrackStore()
         let repository = DefaultRemoteLibraryRepository(
             apiClient: apiClient,
-            store: store
+            store: store,
+            syncCursorStore: syncCursorStore
         )
         let syncService = RemoteLibrarySyncService(
             repository: repository,
@@ -726,6 +728,14 @@ final class iPhoneLibraryViewModel {
         return InMemoryRemoteTrackDownloadStateStore()
     }
 
+    private static func makeRemoteLibrarySyncCursorStore() -> any RemoteLibrarySyncCursorStore {
+        if let store = try? FileRemoteLibrarySyncCursorStore() {
+            return store
+        }
+
+        return InMemoryRemoteLibrarySyncCursorStore()
+    }
+
     private static func makeOfflineAudioFileStore() -> any OfflineAudioFileStore {
         if let store = try? FileOfflineAudioFileStore() {
             return store

apps/apple/VelodyiPhone/Tests/iPhoneLibraryViewModelFavoritesTests.swift

@@ -153,6 +153,36 @@ final class iPhoneLibraryViewModelFavoritesTests: XCTestCase {
         XCTAssertTrue(try XCTUnwrap(remoteRow(in: viewModel, trackID: secondTrack.trackId)).isFavorite)
     }
 
+    func testFavoritesRemainIntactAcrossLibrarySync() async throws {
+        let track = makeRemoteTrack(
+            trackId: "remote-sync-favorite",
+            assetId: "asset-sync-favorite",
+            title: "Sync Favorite"
+        )
+        let favoriteStore = InMemoryFavoriteTrackStore()
+        let viewModel = makeViewModel(
+            remoteTracks: [track],
+            downloadStates: [makeDownloadedState(for: track)],
+            favoriteTrackStore: favoriteStore,
+            audioFiles: [localFilePath(for: track): Data([0x5])],
+            apiClient: StubVelodyAPIClient(
+                environment: ServerEnvironment(
+                    baseURL: ServerEnvironment.defaultLocalBaseURL,
+                    appVersion: "Tests"
+                )
+            )
+        )
+
+        await viewModel.loadIfNeeded()
+        await viewModel.toggleFavorite(trackID: track.trackId)
+        await viewModel.refreshSync()
+
+        XCTAssertTrue(try XCTUnwrap(remoteRow(in: viewModel, trackID: track.trackId)).isFavorite)
+        XCTAssertTrue(try XCTUnwrap(offlineRow(in: viewModel, trackID: track.trackId)).isFavorite)
+        let savedFavorites = try await favoriteStore.loadFavoriteTracks()
+        XCTAssertEqual(savedFavorites.map(\.remoteTrackId), [track.trackId])
+    }
+
     func testToggleFavoriteRepeatedlyLeavesSingleStableRecord() async throws {
         let track = makeRemoteTrack(
             trackId: "remote-repeat",
@@ -285,4 +315,41 @@ final class iPhoneLibraryViewModelFavoritesTests: XCTestCase {
         XCTAssertTrue(remoteTrack.isFavorite)
         XCTAssertTrue(viewModel.availableOfflineTracks.isEmpty)
     }
+
+    func testFailedDownloadKeepsFavoriteAndShowsRetry() async throws {
+        let track = makeRemoteTrack(
+            trackId: "remote-interrupted-favorite",
+            assetId: "asset-interrupted-favorite",
+            title: "Interrupted Favorite"
+        )
+        let viewModel = makeViewModel(
+            remoteTracks: [track],
+            downloadStates: [
+                RemoteTrackDownloadState(
+                    remoteTrackId: track.trackId,
+                    assetId: track.assetId,
+                    localFilePath: "",
+                    downloadedAt: nil,
+                    downloadStatus: .failed,
+                    lastDownloadError: "The previous download did not finish. Try again."
+                ),
+            ],
+            favoriteTrackStore: InMemoryFavoriteTrackStore(tracks: [
+                FavoriteTrackRecord(
+                    remoteTrackId: track.trackId,
+                    favoritedAt: Date(timeIntervalSince1970: 7_000)
+                ),
+            ])
+        )
+
+        await viewModel.loadIfNeeded()
+
+        let remoteTrack = try XCTUnwrap(remoteRow(in: viewModel, trackID: track.trackId))
+
+        XCTAssertEqual(remoteTrack.status, .failed)
+        XCTAssertEqual(remoteTrack.downloadButtonTitle, "Retry")
+        XCTAssertTrue(remoteTrack.canDownload)
+        XCTAssertTrue(remoteTrack.isFavorite)
+        XCTAssertTrue(viewModel.availableOfflineTracks.isEmpty)
+    }
 }

apps/apple/VelodyiPhone/Tests/iPhoneLibraryViewModelPlaybackTests.swift

@@ -4,6 +4,7 @@ import VelodyDomain
 import VelodyNetworking
 import VelodyPlayback
 import VelodyPersistence
+import VelodyUtilities
 @testable import VelodyiPhone
 
 @MainActor
@@ -449,9 +450,35 @@ final class iPhoneLibraryViewModelPolishTests: XCTestCase {
         let remoteTrack = try XCTUnwrap(remoteRow(in: viewModel, trackID: track.trackId))
         XCTAssertEqual(remoteTrack.status, .missing)
         XCTAssertEqual(remoteTrack.statusBadgeTitle, "Missing")
+        XCTAssertTrue(remoteTrack.canDownload)
+        XCTAssertEqual(remoteTrack.downloadButtonTitle, "Re-download")
+        XCTAssertFalse(remoteTrack.canPlay)
         XCTAssertTrue(viewModel.availableOfflineTracks.isEmpty)
         XCTAssertEqual(viewModel.availableOfflineSectionTitle, "Available Offline (0)")
     }
+
+    func testDownloadedTrackAppearsInAvailableOfflineState() async throws {
+        let track = makeRemoteTrack(
+            trackId: "remote-recovered-download",
+            assetId: "asset-recovered-download",
+            title: "Recovered Download"
+        )
+        let viewModel = makeViewModel(
+            remoteTracks: [track],
+            downloadStates: [makeDownloadedState(for: track)],
+            audioFiles: [localFilePath(for: track): Data([0x1, 0x2, 0x3])]
+        )
+
+        await viewModel.loadIfNeeded()
+
+        let remoteTrack = try XCTUnwrap(remoteRow(in: viewModel, trackID: track.trackId))
+        let offlineTrack = try XCTUnwrap(offlineRow(in: viewModel, trackID: track.trackId))
+
+        XCTAssertEqual(remoteTrack.status, .downloaded)
+        XCTAssertEqual(remoteTrack.statusBadgeTitle, "Downloaded")
+        XCTAssertEqual(offlineTrack.statusBadgeTitle, "Downloaded")
+        XCTAssertEqual(viewModel.availableOfflineSectionTitle, "Available Offline (1)")
+    }
 }
 
 @MainActor
@@ -479,7 +506,8 @@ final class iPhoneLibraryViewModelDeviceAuthTests: XCTestCase {
             forKey: "velody.iphone.device-access-token"
         )
 
-        XCTAssertEqual(await counter.count, 1)
+        let registerCount = await counter.currentCount()
+        XCTAssertEqual(registerCount, 1)
         XCTAssertFalse((storedDeviceID ?? "").isEmpty)
         XCTAssertFalse((storedDeviceAccessToken ?? "").isEmpty)
     }
@@ -513,7 +541,8 @@ final class iPhoneLibraryViewModelDeviceAuthTests: XCTestCase {
             forKey: "velody.iphone.device-access-token"
         )
 
-        XCTAssertEqual(await counter.count, 1)
+        let registerCount = await counter.currentCount()
+        XCTAssertEqual(registerCount, 1)
         XCTAssertNotEqual(storedDeviceID, legacyDeviceID)
         XCTAssertFalse((storedDeviceAccessToken ?? "").isEmpty)
     }
@@ -525,6 +554,10 @@ private actor RegisterCallCounter {
     func increment() {
         count += 1
     }
+
+    func currentCount() -> Int {
+        count
+    }
 }
 
 private struct TestRegisterAPIClient: VelodyAPIClient {
@@ -563,6 +596,12 @@ private struct TestRegisterAPIClient: VelodyAPIClient {
         try await stubClient.fetchSyncBootstrap()
     }
 
+    func fetchSyncChanges(
+        cursor: SyncCursor
+    ) async throws -> SyncChangesResponse {
+        try await stubClient.fetchSyncChanges(cursor: cursor)
+    }
+
     func fetchRemoteLibrary(
         deviceId: String
     ) async throws -> RemoteLibraryResponseDTO {