Implement incremental sync and offline recovery

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 {