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lib/shared/services/google_drive_service.dart

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+import 'dart:typed_data';
+import 'package:googleapis/drive/v3.dart' as drive;
+import 'package:google_sign_in/google_sign_in.dart';
+import 'package:extension_google_sign_in_as_googleapis_auth/extension_google_sign_in_as_googleapis_auth.dart';
+
+class DriveBackupResult {
+  final bool success;
+  final String? error;
+  final String? fileId;
+  final DateTime? modifiedTime;
+
+  const DriveBackupResult({this.success = false, this.error, this.fileId, this.modifiedTime});
+
+  factory DriveBackupResult.ok(String fileId, DateTime modifiedTime) =>
+      DriveBackupResult(success: true, fileId: fileId, modifiedTime: modifiedTime);
+
+  factory DriveBackupResult.failed(String error) =>
+      DriveBackupResult(success: false, error: error);
+}
+
+class GoogleDriveService {
+  static const _fileName = 'casha_backup.json';
+  static const _appDataFolder = 'appDataFolder';
+
+  final GoogleSignIn _googleSignIn;
+
+  GoogleDriveService(this._googleSignIn);
+
+  GoogleSignInAccount? get currentUser => _googleSignIn.currentUser;
+  Stream<GoogleSignInAccount?> get onUserChanged => _googleSignIn.onCurrentUserChanged;
+
+  Future<void> signIn() async {
+    await _googleSignIn.signIn();
+  }
+
+  Future<void> signOut() async {
+    await _googleSignIn.signOut();
+  }
+
+  Future<drive.DriveApi?> _getDriveApi() async {
+    if (_googleSignIn.currentUser == null) return null;
+    final httpClient = await _googleSignIn.authenticatedClient();
+    if (httpClient == null) return null;
+    return drive.DriveApi(httpClient);
+  }
+
+  Future<String?> _findExistingFile(drive.DriveApi api) async {
+    final list = await api.files.list(
+      spaces: _appDataFolder,
+      q: "name = '$_fileName' and trashed = false",
+      $fields: 'files(id, name, modifiedTime)',
+    );
+    return list.files?.isNotEmpty == true ? list.files!.first.id : null;
+  }
+
+  Future<DriveBackupResult> uploadBackup(Uint8List data) async {
+    final api = await _getDriveApi();
+    if (api == null) {
+      return DriveBackupResult.failed('Not authenticated');
+    }
+
+    try {
+      final existingId = await _findExistingFile(api);
+
+      final media = drive.Media(
+        Stream<List<int>>.fromIterable([data.toList()]),
+        data.length,
+      );
+
+      if (existingId != null) {
+        final file = drive.File(
+          name: _fileName,
+          modifiedTime: DateTime.now(),
+        );
+        final updated = await api.files.update(
+          file,
+          existingId,
+          uploadMedia: media,
+          $fields: 'id, modifiedTime',
+        );
+        return DriveBackupResult.ok(
+          updated.id!,
+          updated.modifiedTime!,
+        );
+      } else {
+        final file = drive.File(
+          name: _fileName,
+          parents: [_appDataFolder],
+          modifiedTime: DateTime.now(),
+        );
+        final created = await api.files.create(
+          file,
+          uploadMedia: media,
+          $fields: 'id, modifiedTime',
+        );
+        return DriveBackupResult.ok(
+          created.id!,
+          created.modifiedTime!,
+        );
+      }
+    } catch (e) {
+      return DriveBackupResult.failed(e.toString());
+    }
+  }
+
+  Future<Uint8List?> downloadBackup() async {
+    final api = await _getDriveApi();
+    if (api == null) return null;
+
+    try {
+      final fileId = await _findExistingFile(api);
+      if (fileId == null) return null;
+
+      final media = await api.files.get(
+        fileId,
+        downloadOptions: drive.DownloadOptions.fullMedia,
+      ) as drive.Media;
+
+      final bytes = <int>[];
+      await for (final chunk in media.stream) {
+        bytes.addAll(chunk);
+      }
+      return Uint8List.fromList(bytes);
+    } catch (e) {
+      return null;
+    }
+  }
+
+  Future<DateTime?> getLastBackupTime() async {
+    final api = await _getDriveApi();
+    if (api == null) return null;
+
+    try {
+      final list = await api.files.list(
+        spaces: _appDataFolder,
+        q: "name = '$_fileName' and trashed = false",
+        $fields: 'files(id, name, modifiedTime)',
+      );
+      if (list.files?.isNotEmpty == true) {
+        return list.files!.first.modifiedTime;
+      }
+      return null;
+    } catch (e) {
+      return null;
+    }
+  }
+}