import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ChangeNotifierProvider<UserModel>(
        create: (_) => UserModel(),
        child: Consumer<UserModel>(
          builder: (buildContext, model, _) {
            if (model.username == null) {
              return LoginPage();
            } else {
              return HomePage();
            }
          },
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final provider = Provider.of<UserModel>(context, listen: false);

    return Scaffold(
      appBar: AppBar(
        title: Text('Homepage'),
      ),
      body: Container(
        child: Center(
          child: Column(
            children: <Widget>[
              SizedBox(
                height: 32.0,
              ),
              Text('Logged in as ' + provider.username),
              FlatButton(
                color: Color(0xFFDDDDDD),
                child: Text('Logout'),
                onPressed: () {
                  provider.update(null);
                },
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class LoginPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final provider = Provider.of<UserModel>(context, listen: false);

    return Scaffold(
      appBar: AppBar(
        title: Text('Login'),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            SizedBox(
              height: 32.0,
            ),
            Text('Please login'),
            FlatButton(
              color: Color(0xFFDDDDDD),
              child: Text('Login'),
              onPressed: () {
                provider.update('newUser');
              },
            ),
          ],
        ),
      ),
    );
  }
}

class UserModel extends ChangeNotifier {
  String username;

  void update(String newValue) {
    username = newValue;

    notifyListeners();
  }
}