Implement offline mode

lib/core/services/sync_service.dart

@@ -0,0 +1,277 @@
+import 'package:logging/logging.dart';
+
+import '../models/change.dart';
+import '../models/sheet.dart';
+import 'api_client.dart';
+import 'storage_service.dart';
+
+/// Result of a sync operation.
+class SyncResult {
+  final List<Sheet> sheets;
+  final bool isOnline;
+  final int changesSynced;
+  final int annotationsSynced;
+
+  SyncResult({
+    required this.sheets,
+    required this.isOnline,
+    this.changesSynced = 0,
+    this.annotationsSynced = 0,
+  });
+}
+
+/// Service for coordinating offline/online synchronization.
+///
+/// Handles:
+/// - Fetching sheets with offline fallback to cached data
+/// - Uploading pending changes when connection is available
+/// - Uploading pending annotation uploads
+/// - Applying local changes to sheets list
+class SyncService {
+  final _log = Logger('SyncService');
+  final ApiClient _apiClient;
+  final StorageService _storageService;
+
+  SyncService({
+    required ApiClient apiClient,
+    required StorageService storageService,
+  })  : _apiClient = apiClient,
+        _storageService = storageService;
+
+  /// Performs a full sync operation.
+  ///
+  /// 1. Checks if online
+  /// 2. If online: fetches sheets, uploads pending changes, uploads pending annotations
+  /// 3. If offline: loads cached sheets and applies pending changes locally
+  ///
+  /// Returns [SyncResult] with the sheets list and sync status.
+  Future<SyncResult> sync() async {
+    final isOnline = await _apiClient.checkConnection();
+
+    if (isOnline) {
+      return _syncOnline();
+    } else {
+      return _syncOffline();
+    }
+  }
+
+  /// Online sync: fetch from server, upload pending data.
+  Future<SyncResult> _syncOnline() async {
+    _log.info('Online sync starting...');
+
+    int changesSynced = 0;
+    int annotationsSynced = 0;
+
+    // 1. Fetch fresh sheets from server
+    List<Sheet> sheets;
+    try {
+      sheets = await _apiClient.fetchSheets();
+      _log.info('Fetched ${sheets.length} sheets from server');
+
+      // Cache the fetched sheets
+      await _storageService.writeCachedSheets(sheets);
+    } catch (e) {
+      _log.warning('Failed to fetch sheets, falling back to cache: $e');
+      return _syncOffline();
+    }
+
+    // 2. Upload pending changes
+    changesSynced = await _uploadPendingChanges();
+
+    // 3. Upload pending annotations
+    annotationsSynced = await _uploadPendingAnnotations();
+
+    // 4. Apply any remaining local changes (in case some failed to upload)
+    final changeQueue = await _storageService.readChangeQueue();
+    if (changeQueue.isNotEmpty) {
+      try {
+        changeQueue.applyToSheets(sheets);
+        // Update cache with applied changes
+        await _storageService.writeCachedSheets(sheets);
+      } catch (e) {
+        _log.warning('Failed to apply remaining changes: $e');
+      }
+    }
+
+    _log.info(
+      'Online sync complete: $changesSynced changes, $annotationsSynced annotations synced',
+    );
+
+    return SyncResult(
+      sheets: sheets,
+      isOnline: true,
+      changesSynced: changesSynced,
+      annotationsSynced: annotationsSynced,
+    );
+  }
+
+  /// Offline sync: use cached data with local changes applied.
+  Future<SyncResult> _syncOffline() async {
+    _log.info('Offline mode: loading cached data...');
+
+    // 1. Load cached sheets
+    var sheets = await _storageService.readCachedSheets();
+
+    if (sheets.isEmpty) {
+      _log.warning('No cached sheets available in offline mode');
+    }
+
+    // 2. Apply pending changes locally
+    final changeQueue = await _storageService.readChangeQueue();
+    if (changeQueue.isNotEmpty) {
+      _log.info('Applying ${changeQueue.length} pending changes locally');
+      try {
+        changeQueue.applyToSheets(sheets);
+      } catch (e) {
+        _log.warning('Failed to apply some changes: $e');
+      }
+    }
+
+    return SyncResult(
+      sheets: sheets,
+      isOnline: false,
+    );
+  }
+
+  /// Uploads all pending changes to the server.
+  ///
+  /// Returns the number of successfully synced changes.
+  Future<int> _uploadPendingChanges() async {
+    final changes = await _storageService.readChangeList();
+    if (changes.isEmpty) return 0;
+
+    _log.info('Uploading ${changes.length} pending changes...');
+
+    try {
+      final appliedIndices = await _apiClient.uploadChanges(changes);
+
+      // Delete successfully synced changes (in reverse order to maintain indices)
+      for (int i = appliedIndices.length - 1; i >= 0; i--) {
+        await _storageService.deleteOldestChange();
+      }
+
+      _log.info('${appliedIndices.length} changes synced successfully');
+      return appliedIndices.length;
+    } catch (e) {
+      _log.warning('Failed to upload changes: $e');
+      return 0;
+    }
+  }
+
+  /// Uploads all pending annotation uploads to the server.
+  ///
+  /// Returns the number of successfully synced annotations.
+  Future<int> _uploadPendingAnnotations() async {
+    final pendingUploads = await _storageService.readPendingAnnotationUploads();
+    if (pendingUploads.isEmpty) return 0;
+
+    _log.info('Uploading ${pendingUploads.length} pending annotations...');
+
+    int syncedCount = 0;
+
+    for (final upload in pendingUploads) {
+      try {
+        await _apiClient.uploadAnnotation(
+          sheetUuid: upload.sheetUuid,
+          page: upload.page,
+          lastModified: upload.lastModified,
+          annotationsJson: upload.annotationsJson,
+        );
+
+        // Delete from pending queue after successful upload
+        await _storageService.deletePendingAnnotationUpload(upload.key);
+        syncedCount++;
+      } catch (e) {
+        _log.warning(
+          'Failed to upload annotation for ${upload.sheetUuid} page ${upload.page}: $e',
+        );
+        // Continue with other uploads
+      }
+    }
+
+    _log.info('$syncedCount annotations synced successfully');
+    return syncedCount;
+  }
+
+  /// Queues a change for sync.
+  ///
+  /// If online, attempts immediate upload. Otherwise, stores locally.
+  Future<void> queueChange(Change change) async {
+    // Always store locally first
+    await _storageService.writeChange(change);
+
+    // Try to upload immediately if online
+    try {
+      final isOnline = await _apiClient.checkConnection();
+      if (isOnline) {
+        final changes = await _storageService.readChangeList();
+        final appliedIndices = await _apiClient.uploadChanges(changes);
+
+        // Delete synced changes
+        for (int i = 0; i < appliedIndices.length; i++) {
+          await _storageService.deleteOldestChange();
+        }
+      }
+    } catch (e) {
+      _log.fine('Immediate upload failed, change queued for later: $e');
+    }
+  }
+
+  /// Queues an annotation upload.
+  ///
+  /// If the upload fails (e.g., offline), it will be stored for later sync.
+  Future<bool> uploadAnnotationWithFallback({
+    required String sheetUuid,
+    required int page,
+    required String annotationsJson,
+    required DateTime lastModified,
+  }) async {
+    try {
+      await _apiClient.uploadAnnotation(
+        sheetUuid: sheetUuid,
+        page: page,
+        lastModified: lastModified,
+        annotationsJson: annotationsJson,
+      );
+      return true;
+    } catch (e) {
+      _log.fine('Annotation upload failed, queuing for later: $e');
+
+      // Store for later upload
+      await _storageService.writePendingAnnotationUpload(
+        PendingAnnotationUpload(
+          sheetUuid: sheetUuid,
+          page: page,
+          annotationsJson: annotationsJson,
+          lastModified: lastModified,
+        ),
+      );
+      return false;
+    }
+  }
+
+  /// Updates the local cache after a sheet edit.
+  ///
+  /// Call this after applying changes to the sheets list locally.
+  Future<void> updateCachedSheets(List<Sheet> sheets) async {
+    await _storageService.writeCachedSheets(sheets);
+  }
+
+  /// Gets the number of pending changes.
+  Future<int> getPendingChangesCount() async {
+    return _storageService.getChangeQueueLength();
+  }
+
+  /// Gets the number of pending annotation uploads.
+  Future<int> getPendingAnnotationsCount() async {
+    final uploads = await _storageService.readPendingAnnotationUploads();
+    return uploads.length;
+  }
+
+  /// Checks if there is any pending data to sync.
+  Future<bool> hasPendingData() async {
+    final changesCount = await getPendingChangesCount();
+    final annotationsCount = await getPendingAnnotationsCount();
+    return changesCount > 0 || annotationsCount > 0;
+  }
+}