main.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

//*********************************************
// APP entry point
//*********************************************
void main() => runApp(
      const ProviderScope(child: App()),
    );

//*********************************************
// PROVIDERS
//*********************************************

// I couldn't import Dio here, so I'm just creating this "dump" dio class.
// but hte idea is to use it where I would need it in my actual app for http requests
class Dio {
  final String baseUrl;
  
  const Dio(this.baseUrl);
  
  // fake, only used since we don't have url nor user
  Future<User> get(String path) {
    return Future.delayed(const Duration(seconds: 3), () => const User("fake-id-231"));
  }
}

final tokenizedDio = FutureProvider.autoDispose<Dio>((ref) async {
  // mimic the idea of a url coming from a remote config.
  const duration = Duration(seconds: 5);
  final url = await Future.delayed(duration, () => 'http://google.com/api');
  
  return Dio(url);
});

final userApiProvider = Provider<UserApi>((ref) {
  // I want to get a Future<Dio>, so that waiting on it would result in some Dio
  // that the UserApiImpl can use
  // final Future<Dio> futureDio = ref.watch(tokenizedDio);
  final Future<Dio> futureDio = ref.read(tokenizedDio.future);
  return UserApiImpl(futureDio);
});

//*********************************************
// API
//*********************************************

class User {
  final String id;
  
  const User(this.id);
}

abstract class UserApi {
  Future<User> getCurrentUser();
}

class UserApiImpl implements UserApi {
  final Future<Dio> _dio;
  
  const UserApiImpl(this._dio);
  
  static const kPathCurrentUser = "/api/user/@me";
  
  @override
  Future<User> getCurrentUser() async {
    final dio = await _dio;
    final response = await dio.get(kPathCurrentUser);
    // this
    return response;
  }
}

//*********************************************
// App root
//*********************************************
class App extends ConsumerWidget {
  const App({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) => const MaterialApp(
        title: 'Riverpod Navigator Example',
        debugShowCheckedModeBanner: false,
        home: HomeScreen()
      );
}

//*********************************************
// Widgets
//*********************************************

class HomeScreen extends StatelessWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: const Text('Sample.1'),
        ),
        body: const Center(
          child: WaitForUserWidget()
        ),
      );
}

class WaitForUserWidget extends ConsumerWidget {
  const WaitForUserWidget({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final userApi = ref.watch(userApiProvider);
    
    return FutureBuilder<User>(future: userApi.getCurrentUser(), builder: (context, snapshot) {
      if (snapshot.connectionState == ConnectionState.done) {
        final User user = snapshot.data!;
        return Text(user.id);
      }
      return const CircularProgressIndicator();
    });
  }
}