feat(SNP-1314): Down by Maintenance

lib/features/app/app.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_easy_dialogs/flutter_easy_dialogs.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
+import 'package:flutter_template/features/down_for_maintenance/presentation/down_for_maintenance_widget.dart';
 import 'package:flutter_template/features/navigation/app_router.dart';
 import 'package:flutter_template/features/snack_queue/presentation/snack_queue_provider.dart';
 import 'package:flutter_template/features/theme_mode/presentation/widgets/theme_mode_builder.dart';
@@ -53,7 +54,7 @@ class _AppState extends State<App> {
             final mediaQueryData = MediaQuery.of(builderContext);
             final easyDialogsBuilder = FlutterEasyDialogs.builder();
 
-            return Nested(
+            final child = Nested(
               children: const [
                 SnackQueueProvider(),
               ],
@@ -68,6 +69,11 @@ class _AppState extends State<App> {
                 ),
               ),
             );
+
+            // TODO(init): Uncomment it or delete if you don't need it.
+            return DownForMaintenanceWidget(child: child);
+
+            // return child;
           },
 
           /// Localization.

lib/features/app/di/app_scope_register.dart

@@ -47,6 +47,14 @@ final class AppScopeRegister {
     });
     final logger = LogWriter(surfLogger);
 
+    // TODO(init-project): In order to use Down For Maintenance feature you have to:
+    // - create implementation of [ICheckServerStatusRepository] here
+    // - call [ICheckServerStatusRepository.configure] and await for it
+    // - call [ICheckServerStatusRepository.initImmediateCheck]
+    // - add it to AppScope
+    // - add DownForMaintenanceWidget in builder of MaterialApp in app.dart
+    // Otherwise just delete this.
+
     return AppScope(
       env: env,
       appConfig: appConfig,

lib/features/down_for_maintenance/data/repository/fb_check_server_status_repository.dart

@@ -0,0 +1,39 @@
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/repository/i_check_server_status_repository.dart';
+import 'package:rxdart/rxdart.dart';
+
+/// Implementation of [ICheckServerStatusRepository] that uses Firebase Remote Config to check server status.
+class FirebaseCheckServerStatusRepository implements ICheckServerStatusRepository {
+  @override
+  final BehaviorSubject<ServerCheckResult> serverStatus = BehaviorSubject.seeded(ServerCheckResult.processing);
+
+  @override
+  Future<void> configurate() async {
+    /// Here you can configurate your Firebase Remote Config interval of requests for example.
+    /// For example:
+    //
+    // await remoteConfig.setConfigSettings(RemoteConfigSettings(
+    // fetchTimeout: const Duration(minutes: 1),
+    // minimumFetchInterval: const Duration(hours: 1),
+    // ));
+    //
+  }
+
+  @override
+  Future<void> initImmediateCheck() async {
+    /// Here you can make a request to your Firebase Remote Config to check if it is available.
+    /// For example:
+    // try {
+    //   await remoteConfig.fetchAndActivate();
+    //   final isServerAvailable = remoteConfig.getBool('is_server_available');
+    //   serverStatus.value = isServerAvailable ? ServerCheckResult.worksNormally : ServerCheckResult.notActive;
+    // } on Exception catch (_) {
+    //   serverStatus.value = ServerCheckResult.errorOccurred;
+    // }
+  }
+
+  @override
+  void dispose() {
+    serverStatus.close();
+  }
+}

lib/features/down_for_maintenance/data/repository/mock_check_server_status_repository.dart

@@ -0,0 +1,38 @@
+import 'dart:async';
+
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/repository/i_check_server_status_repository.dart';
+import 'package:rxdart/rxdart.dart';
+
+/// Implementation of [ICheckServerStatusRepository] that mocks server status.
+class MockCheckServerStatusRepository implements ICheckServerStatusRepository {
+  @override
+  final BehaviorSubject<ServerCheckResult> serverStatus = BehaviorSubject.seeded(ServerCheckResult.processing);
+
+  late final Timer _timer;
+
+  @override
+  Future<void> configurate() async {
+    _check().ignore();
+    _timer = Timer.periodic(const Duration(minutes: 5), (timer) {
+      _check();
+    });
+  }
+
+  @override
+  void initImmediateCheck() {
+    serverStatus.value = ServerCheckResult.processing;
+    _check();
+  }
+
+  Future<void> _check() async {
+    await Future.delayed(const Duration(seconds: 1));
+    serverStatus.value = ServerCheckResult.worksNormally;
+  }
+
+  @override
+  void dispose() {
+    _timer.cancel();
+    serverStatus.close();
+  }
+}

lib/features/down_for_maintenance/data/repository/rest_check_server_status_repository.dart

@@ -0,0 +1,37 @@
+import 'package:dio/dio.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/repository/i_check_server_status_repository.dart';
+import 'package:rxdart/rxdart.dart';
+
+/// Implementation of [ICheckServerStatusRepository] that uses REST API to check server status.
+class RestCheckServerStatusRepository implements ICheckServerStatusRepository {
+  // ignore: unused_field
+  final Dio _dio;
+
+  /// @nodoc
+  RestCheckServerStatusRepository(this._dio);
+
+  @override
+  final BehaviorSubject<ServerCheckResult> serverStatus = BehaviorSubject.seeded(ServerCheckResult.processing);
+
+  @override
+  Future<void> configurate() async {
+    /// Here you can configurate your client to make requests every n minutes for example.
+    /// For example:
+    ///
+    // _timer = Timer.periodic(Duration(minutes: 5), (timer) {
+    //      initImmediateCheck();
+    //   });
+  }
+
+  @override
+  void initImmediateCheck() {
+    /// Here you can make a request to your server to check if it is available.
+  }
+
+  @override
+  void dispose() {
+    // _timer.cancel();
+    serverStatus.close();
+  }
+}

lib/features/down_for_maintenance/domain/entities/server_check_result.dart

@@ -0,0 +1,14 @@
+/// Server check result enum.
+enum ServerCheckResult {
+  /// Server works normally.
+  worksNormally,
+
+  /// Server is not active.
+  notActive,
+
+  /// Error occurred during server check.
+  errorOccurred,
+
+  /// Server check is in progress.
+  processing,
+}

lib/features/down_for_maintenance/domain/repository/i_check_server_status_repository.dart

@@ -0,0 +1,16 @@
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+
+/// Interface for checking server status.
+abstract interface class ICheckServerStatusRepository {
+  /// Current state of server.
+  Stream<ServerCheckResult> get serverStatus;
+
+  /// Method that initiate check of current server status.
+  void initImmediateCheck();
+
+  /// Method that configurate service. For example, you can configurate interval of requests.
+  Future<void> configurate();
+
+  /// Method that dispose service. For example, you can cancel timers.
+  void dispose();
+}

lib/features/down_for_maintenance/domain/services/check_server_status_service.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+
+/// Interface for checking server status.
+abstract interface class ICheckServerStatusService {
+  /// Current state of server.
+  ValueListenable<ServerCheckResult> get serverStatus;
+
+  /// Method that initiate check of current server status.
+  void initImmediateCheck();
+
+  /// Method that configurate service. For example, you can configurate interval of requests.
+  Future<void> configurate();
+
+  /// Method that dispose service. For example, you can cancel timers.
+  void dispose();
+}

lib/features/down_for_maintenance/presentation/down_for_maintenance_model.dart

@@ -0,0 +1,40 @@
+import 'dart:async';
+
+import 'package:elementary/elementary.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/repository/i_check_server_status_repository.dart';
+
+/// Model with businness-logic for Down For Maintenance feature.
+class DownForMaintenanceModel extends ElementaryModel {
+  final ICheckServerStatusRepository _checkServerStatusRepository;
+  final _serverCheckResult = ValueNotifier(ServerCheckResult.processing);
+
+  /// Current server status.
+  ValueListenable<ServerCheckResult> get serverCheckResult => _serverCheckResult;
+  late StreamSubscription<ServerCheckResult> _streamSubscription;
+
+  /// @nodoc
+  DownForMaintenanceModel(this._checkServerStatusRepository);
+
+  @override
+  void init() {
+    _streamSubscription = _checkServerStatusRepository.serverStatus.listen((event) {
+      _serverCheckResult.value = event;
+    });
+    super.init();
+  }
+
+  /// Initiates immediate check of server status.
+  void initImmediateCheck() {
+    _checkServerStatusRepository.initImmediateCheck();
+  }
+
+  @override
+  void dispose() {
+    _streamSubscription.cancel();
+    _serverCheckResult.dispose();
+    _checkServerStatusRepository.dispose();
+    super.dispose();
+  }
+}

lib/features/down_for_maintenance/presentation/down_for_maintenance_widget.dart

@@ -0,0 +1,57 @@
+import 'package:elementary/elementary.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/presentation/down_for_maintenance_wm.dart';
+
+/// Widget that shows child widget if server works normally or shows placeholder if server is down.
+class DownForMaintenanceWidget extends ElementaryWidget<IDownForMaintenanceWM> {
+  /// Child widget that will be shown if server works normally. Usually it is whole application, but
+  /// you also can use it for some part of application (e.g. some feature).
+  final Widget child;
+
+  /// @nodoc
+  const DownForMaintenanceWidget({
+    required this.child,
+    super.key,
+  }) : super(defaultDownForMaintenanceWMFactory);
+
+  @override
+  Widget build(IDownForMaintenanceWM wm) {
+    return ValueListenableBuilder(
+      valueListenable: wm.currentResult,
+      builder: (_, status, __) => switch (status) {
+        ServerCheckResult.errorOccurred || ServerCheckResult.notActive => _PlaceholderWidget(
+            onRetryPressed: wm.onCheckCurrentStatusPressed,
+          ),
+        ServerCheckResult.processing => const Center(child: CircularProgressIndicator()),
+        ServerCheckResult.worksNormally => child,
+      },
+    );
+  }
+}
+
+/// Placeholder widget that shows when server is not available.
+/// Replace it with your own widget.
+class _PlaceholderWidget extends StatelessWidget {
+  final VoidCallback onRetryPressed;
+  const _PlaceholderWidget({required this.onRetryPressed});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: Center(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            const Text('Server is not available now. Please try again later.'),
+            const SizedBox(height: 10),
+            ElevatedButton(
+              onPressed: onRetryPressed,
+              child: const Text('Retry'),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

lib/features/down_for_maintenance/presentation/down_for_maintenance_wm.dart

@@ -0,0 +1,36 @@
+import 'package:elementary/elementary.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_template/features/down_for_maintenance/data/repository/mock_check_server_status_repository.dart';
+import 'package:flutter_template/features/down_for_maintenance/domain/entities/server_check_result.dart';
+import 'package:flutter_template/features/down_for_maintenance/presentation/down_for_maintenance_model.dart';
+import 'package:flutter_template/features/down_for_maintenance/presentation/down_for_maintenance_widget.dart';
+
+/// Factory that creates DownForMaintenanceWM.
+DownForMaintenanceWM defaultDownForMaintenanceWMFactory(BuildContext context) {
+  return DownForMaintenanceWM(DownForMaintenanceModel(MockCheckServerStatusRepository()));
+}
+
+/// WidgetModel for DownForMaintenanceWidget.
+class DownForMaintenanceWM extends WidgetModel<DownForMaintenanceWidget, DownForMaintenanceModel>
+    implements IDownForMaintenanceWM {
+  @override
+  ValueListenable<ServerCheckResult> get currentResult => model.serverCheckResult;
+
+  /// @nodoc
+  DownForMaintenanceWM(super._model);
+
+  @override
+  void onCheckCurrentStatusPressed() {
+    model.initImmediateCheck();
+  }
+}
+
+/// Interface for DownForMaintenanceWM.
+abstract interface class IDownForMaintenanceWM implements IWidgetModel {
+  /// Current state of server.
+  ValueListenable<ServerCheckResult> get currentResult;
+
+  /// Callback that initiate check of current server status.
+  void onCheckCurrentStatusPressed();
+}