Flutter Android login vault: local DB (id+base64 content), email/Google auth, dashboard search/edit/swipe-delete, dark/system theme, minSdk 29

lib/auth_service.dart

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+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:login_vault_app/constants.dart';
+
+/// Handles app-level authentication and persistence of the local identity.
+///
+/// On first launch the user registers (email+password OR Google). The chosen
+/// email is stored locally as the key ([AppConstants.secureKeyEmail]) and the
+/// app password (used to lock the dashboard) is stored in secure storage.
+class AuthService {
+  final FlutterSecureStorage _storage = const FlutterSecureStorage();
+
+  /// Returns the stored email, or null if not registered yet.
+  Future<String?> getEmail() async =>
+      await _storage.read(key: AppConstants.secureKeyEmail);
+
+  Future<String?> getAppPassword() async =>
+      await _storage.read(key: AppConstants.secureKeyAppPassword);
+
+  /// True if a user identity already exists locally.
+  Future<bool> isRegistered() async => (await getEmail()) != null;
+
+  /// Register with email + app password.
+  Future<void> registerWithEmail(String email, String appPassword) async {
+    await _storage.write(key: AppConstants.secureKeyEmail, value: email);
+    await _storage.write(
+        key: AppConstants.secureKeyAppPassword, value: appPassword);
+  }
+
+  /// Register with Google (email supplied by Google sign-in).
+  Future<void> registerWithGoogle(String email) async {
+    await _storage.write(key: AppConstants.secureKeyEmail, value: email);
+    // App password defaults to a marker; user can change it later in settings.
+    final existing = await getAppPassword();
+    if (existing == null) {
+      await _storage.write(
+          key: AppConstants.secureKeyAppPassword, value: '__google__');
+    }
+  }
+
+  /// Verify the entered app password against the stored one.
+  Future<bool> verifyPassword(String password) async {
+    final stored = await getAppPassword();
+    if (stored == null) return false;
+    if (stored == '__google__') {
+      // Google users have no password by default; let any entry pass OR force set.
+      return true;
+    }
+    return stored == password;
+  }
+
+  /// Change the app password (used in settings).
+  Future<void> changePassword(String newPassword) async {
+    await _storage.write(
+        key: AppConstants.secureKeyAppPassword, value: newPassword);
+  }
+
+  Future<void> logout() async {
+    // Keep email (identity) but we treat logout as returning to auth screen
+    // with the email still known. To fully reset, call [reset].
+  }
+
+  /// Wipe local identity (for completeness / debugging).
+  Future<void> reset() async {
+    await _storage.delete(key: AppConstants.secureKeyEmail);
+    await _storage.delete(key: AppConstants.secureKeyAppPassword);
+  }
+}