Standard AuthenticationBloc for Flutter Firebase authentication

// MIT licence
import 'dart:async';
import 'dart:io';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:fluent_academy_app/blocs/initializable_cubit.dart';
import 'package:fluent_academy_app/widgets/user/auth/signin/sign_in_providers.dart';
import 'package:flutter/widgets.dart';
import 'package:firebase_auth/firebase_auth.dart' as auth;
import 'package:google_sign_in/google_sign_in.dart';
import 'package:sign_in_with_apple/sign_in_with_apple.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'dart:math';
import 'dart:convert';
import 'dart:io';
import 'package:crypto/crypto.dart';
import 'package:sign_in_with_apple/sign_in_with_apple.dart';


enum SignInProviders { Google, Email, Twitter, Apple }

Map<SignInProviders, String> signInLabels = {
  SignInProviders.Apple: "Apple",
  SignInProviders.Google: "Google",
  SignInProviders.Twitter: "Twitter",
  SignInProviders.Email: "Email",
};


Map<String, SignInProviders> signInProviderIds = {
  "password": SignInProviders.Email,
  "twitter.com": SignInProviders.Twitter,
  "google.com": SignInProviders.Google,
  "apple": SignInProviders.Apple
};


class AuthenticationBlocState with InitializableState {
  bool isAuthenticated = false;
  bool authenticating = false;
  bool hasConnection = false;
  bool checkingConnection = false;
  String? uid;

  @override
  AuthenticationBlocState copy() {
    return AuthenticationBlocState()
      ..authenticating = authenticating
      ..hasConnection = hasConnection
      ..isAuthenticated = isAuthenticated
      ..initializer = initializer;
  }
}

class AuthenticationBloc extends InitializableCubit<AuthenticationBlocState> {
  auth.User? get user => auth.FirebaseAuth.instance.currentUser;

  AuthenticationBloc()
      : super(AuthenticationBlocState()..isAuthenticated = false);

  Future<bool> initialize(BuildContext context) async {
    await Firebase.initializeApp();

    auth.FirebaseAuth.instance.authStateChanges().listen((user) {
      emit(state.copy()
        ..uid = user?.uid
        ..isAuthenticated = user != null);
    });

    if (user != null) {
      emit(state.copy()
        ..isAuthenticated = true
        ..uid = user!.uid);
    } else {
      try {
        emit(state.copy()..checkingConnection = true);
        final result = await InternetAddress.lookup('google.com');
        if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
          emit(state.copy()
            ..checkingConnection = false
            ..hasConnection = true);
        }
      } on SocketException catch (_) {
        emit(state.copy()
          ..checkingConnection = false
          ..hasConnection = false);
      }
    }
    return super.initialize(context);
  }

  String _createNonce(int length) {
    final random = Random();
    final charCodes = List<int>.generate(length, (_) {
      late int codeUnit;

      switch (random.nextInt(3)) {
        case 0:
          codeUnit = random.nextInt(10) + 48;
          break;
        case 1:
          codeUnit = random.nextInt(26) + 65;
          break;
        case 2:
          codeUnit = random.nextInt(26) + 97;
          break;
      }

      return codeUnit;
    });

    return String.fromCharCodes(charCodes);
  }

  Future<OAuthCredential> _createAppleOAuthCred() async {
    final nonce = _createNonce(32);
    final nativeAppleCred = Platform.isIOS
        ? await SignInWithApple.getAppleIDCredential(
            scopes: [
              AppleIDAuthorizationScopes.email,
              AppleIDAuthorizationScopes.fullName,
            ],
            nonce: sha256.convert(utf8.encode(nonce)).toString(),
          )
        : await SignInWithApple.getAppleIDCredential(
            scopes: [
              AppleIDAuthorizationScopes.email,
              AppleIDAuthorizationScopes.fullName,
            ],
            webAuthenticationOptions: WebAuthenticationOptions(
              redirectUri: Uri.parse(
                  WEB_HANDLER),
              clientId: CLIENT_ID,
            ),
            nonce: sha256.convert(utf8.encode(nonce)).toString(),
          );

    return new OAuthCredential(
      providerId: "apple.com", // MUST be "apple.com"
      signInMethod: "oauth", // MUST be "oauth"
      accessToken: nativeAppleCred
          .identityToken, // propagate Apple ID token to BOTH accessToken and idToken parameters
      idToken: nativeAppleCred.identityToken,
      rawNonce: nonce,
    );
  }

  Future<bool> signInWithApple() async {
    final oauthCred = await _createAppleOAuthCred();
    await FirebaseAuth.instance.signInWithCredential(oauthCred);
    return true;
  }

  Future<bool> signInWithGoogle() async {
    final GoogleSignIn _googleSignIn = GoogleSignIn();
    GoogleSignInAccount? googleUser = await _googleSignIn.signIn();

    if(googleUser == null)
      return false;

    GoogleSignInAuthentication googleAuth = await googleUser!.authentication;
    AuthCredential credential = GoogleAuthProvider.credential(
        idToken: googleAuth.idToken, accessToken: googleAuth.accessToken);
    await FirebaseAuth.instance.signInWithCredential(credential);
    return true;
  }

  Future<bool> signInWithProvider(SignInProviders provider) async {
    switch (provider) {
      case SignInProviders.Apple:
        return signInWithApple();
      case SignInProviders.Google:
        return signInWithGoogle();
      default:
        throw UnsupportedError("Provider $provider not yet supported");
    }
  }

  Future logout() async {
    await auth.FirebaseAuth.instance.signOut();
    emit(state.copy()..isAuthenticated = false);
  }
}