import 'dart:io';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Google Sign-in bug demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Google Sign-in bug demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  static final _clientId = 'google client id';

  final _googleSignIn = GoogleSignIn(clientId: _clientId);
  bool loading = false;
  bool signedIn = false;

  @override
  void initState() {
    super.initState();

    // relying on changes in the stream to update auth status
    _googleSignIn.onCurrentUserChanged.listen((acc) {
      setState(() {
        loading = false;
        signedIn = acc != null;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            if (loading)
              ...[
                Text('loading auth state'),
                CircularProgressIndicator(),
              ]
            else if (signedIn)
              ...[
                Text('you\'re signed in!'),
                ElevatedButton(onPressed: _doGoogleSignOut, child: Text('sign out')),
              ]
            else
              ElevatedButton(onPressed: _doGoogleSignIn, child: Text('sign in with google')),
          ],
        ),
      ),
    );
  }

  void _doGoogleSignIn() {
    setState(() {
      loading = true;

      // when a user cancels the auth process, the future returned by the following request will complete with `null`,
      // however, the `_googleSignIn.onCurrentUserChanged` `Stream` does not emit a new `null` value,
      // nor is an error thrown. this means that we can't use a consistent approach (i.e., relying solely on the stream)
      // to handle the canceled auth flow scenario, and have to also await this future and see if the result is null
      _googleSignIn.signIn();
    });
  }

  void _doGoogleSignOut() {
    setState(() {
      loading = true;
      _googleSignIn.signOut();
    });
  }
}