Add AppStartupWidget class for asynchronous app initialization

lib/main.dart

@@ -1,31 +1,24 @@
-import 'package:firebase_core/firebase_core.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
-import 'package:starter_architecture_flutter_firebase/firebase_options.dart';
 import 'package:starter_architecture_flutter_firebase/src/app.dart';
+import 'package:starter_architecture_flutter_firebase/src/app_startup.dart';
 import 'package:starter_architecture_flutter_firebase/src/localization/string_hardcoded.dart';
-import 'package:starter_architecture_flutter_firebase/src/features/onboarding/data/onboarding_repository.dart';
 // ignore:depend_on_referenced_packages
 import 'package:flutter_web_plugins/url_strategy.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  await Firebase.initializeApp(
-    options: DefaultFirebaseOptions.currentPlatform,
-  );
   // turn off the # in the URLs on the web
   usePathUrlStrategy();
   // * Register error handlers. For more info, see:
   // * https://docs.flutter.dev/testing/errors
   registerErrorHandlers();
   // * Entry point of the app
-
-  final container = ProviderContainer();
-  await container.read(onboardingRepositoryProvider.future);
-  runApp(UncontrolledProviderScope(
-    container: container,
-    child: const MyApp(),
+  runApp(ProviderScope(
+    child: AppStartupWidget(
+      onLoaded: (context) => const MyApp(),
+    ),
   ));
 }
 

lib/src/app_startup.dart

@@ -0,0 +1,85 @@
+import 'package:firebase_core/firebase_core.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+import 'package:starter_architecture_flutter_firebase/firebase_options.dart';
+import 'package:starter_architecture_flutter_firebase/src/constants/app_sizes.dart';
+import 'package:starter_architecture_flutter_firebase/src/features/onboarding/data/onboarding_repository.dart';
+
+part 'app_startup.g.dart';
+
+@Riverpod(keepAlive: true)
+Future<void> appStartup(AppStartupRef ref) async {
+  // await for all initialization code to be complete before returning
+  await Future.wait([
+    // Firebase init
+    Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform),
+    // list of providers to be warmed up
+    ref.watch(onboardingRepositoryProvider.future)
+  ]);
+}
+
+/// Widget class to manage asynchronous app initialization
+class AppStartupWidget extends ConsumerWidget {
+  const AppStartupWidget({super.key, required this.onLoaded});
+  final WidgetBuilder onLoaded;
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final appStartupState = ref.watch(appStartupProvider);
+    return appStartupState.when(
+      data: (_) => onLoaded(context),
+      loading: () => const AppStartupLoadingWidget(),
+      error: (e, st) => AppStartupErrorWidget(
+        message: e.toString(),
+        onRetry: () {
+          ref.invalidate(onboardingRepositoryProvider);
+          ref.invalidate(appStartupProvider);
+        },
+      ),
+    );
+  }
+}
+
+class AppStartupLoadingWidget extends StatelessWidget {
+  const AppStartupLoadingWidget({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      home: Scaffold(
+        body: Center(
+          child: CircularProgressIndicator(),
+        ),
+      ),
+    );
+  }
+}
+
+class AppStartupErrorWidget extends StatelessWidget {
+  const AppStartupErrorWidget(
+      {super.key, required this.message, required this.onRetry});
+  final String message;
+  final VoidCallback onRetry;
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        body: Center(
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              Text(message, style: Theme.of(context).textTheme.headlineSmall),
+              gapH16,
+              ElevatedButton(
+                onPressed: onRetry,
+                child: const Text('Retry'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}