Google Sign-In Setup

dependencies:
  firebase_auth: any
  google_sign_in: any
  firebase_core: any
  cloud_firestore: any

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.app_tareas">
    
    <!-- Internet permission required for Google Sign-In -->
    <uses-permission android:name="android.permission.INTERNET"/>
    
    <application
        android:label="App Tareas"
        android:name="${applicationName}"
        android:icon="@mipmap/ic_launcher">
        
        <activity
            android:name=".MainActivity"
            android:exported="true"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
        
        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />
    </application>
</manifest>

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'com.google.gms.google-services'  // Required for Google Sign-In
    id 'dev.flutter.flutter-gradle-plugin'
}

android {
    namespace 'com.example.app_tareas'
    compileSdkVersion flutter.compileSdkVersion
    
    defaultConfig {
        applicationId 'com.example.app_tareas'
        minSdkVersion 23  // Google Sign-In requires min SDK 23
        targetSdkVersion flutter.targetSdkVersion
    }
}

import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:logger/logger.dart';

class AuthService {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;
  final Logger _logger = Logger();

  /// Sign in with Google Account
  /// Returns the authenticated User or null if sign-in fails
  Future<User?> signInWithGoogle() async {
    try {
      // Trigger the Google Sign-In flow
      final GoogleSignInAccount? googleUser = await _googleSignIn.signIn();
      
      // User cancelled the sign-in
      if (googleUser == null) return null;

      // Obtain auth details from the Google Sign-In request
      final GoogleSignInAuthentication googleAuth = 
          await googleUser.authentication;
      
      // Create a new credential with the tokens
      final AuthCredential credential = GoogleAuthProvider.credential(
        accessToken: googleAuth.accessToken,
        idToken: googleAuth.idToken,
      );

      // Sign in to Firebase with the Google credential
      final UserCredential userCredential = 
          await _auth.signInWithCredential(credential);
      User? user = userCredential.user;

      // Check if user profile exists in Firestore
      DocumentSnapshot userDoc = 
          await _firestore.collection('users').doc(user!.uid).get();
      
      if (!userDoc.exists) {
        // Create user profile for first-time users
        await _firestore.collection('users').doc(user.uid).set({
          'name': user.displayName ?? 'Sin nombre',
          'surname': '',
          'email': user.email,
          'photoUrl': user.photoURL,
          'createdAt': FieldValue.serverTimestamp(),
        });
        _logger.i('New user profile created for: ${user.email}');
      }

      return user;
    } catch (e) {
      _logger.e('Error signing in with Google: $e');
      return null;
    }
  }

  /// Sign out from both Firebase and Google
  Future<void> signOut() async {
    await _auth.signOut();
    await _googleSignIn.signOut();
  }
}

import 'package:flutter/material.dart';
import 'package:app_tareas/services/auth_service.dart';

class LoginScreen extends StatefulWidget {
  const LoginScreen({Key? key}) : super(key: key);

  @override
  State<LoginScreen> createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  final AuthService _authService = AuthService();
  bool _isLoading = false;

  Future<void> _handleGoogleSignIn() async {
    setState(() => _isLoading = true);
    
    try {
      final user = await _authService.signInWithGoogle();
      
      if (user != null && mounted) {
        // Navigate to home screen
        Navigator.pushReplacementNamed(context, '/home');
      } else {
        // User cancelled or sign-in failed
        _showErrorDialog('Sign-in cancelled or failed');
      }
    } catch (e) {
      _showErrorDialog('Error: $e');
    } finally {
      if (mounted) {
        setState(() => _isLoading = false);
      }
    }
  }

  void _showErrorDialog(String message) {
    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('Sign-In Error'),
        content: Text(message),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: const Text('OK'),
          ),
        ],
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: _isLoading
            ? const CircularProgressIndicator()
            : ElevatedButton.icon(
                onPressed: _handleGoogleSignIn,
                icon: Image.asset('assets/google_logo.png', height: 24),
                label: const Text('Sign in with Google'),
                style: ElevatedButton.styleFrom(
                  backgroundColor: Colors.white,
                  foregroundColor: Colors.black87,
                  padding: const EdgeInsets.symmetric(
                    horizontal: 24,
                    vertical: 12,
                  ),
                ),
              ),
      ),
    );
  }
}