import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in_platform_interface/google_sign_in_platform_interface.dart';
import 'package:travel_mate/services/error_service.dart';

/// Service for handling Firebase authentication operations.
/// 
/// This service provides methods for user authentication including email/password
/// sign-in, Google sign-in, Apple sign-in, password reset, and account management.
/// It acts as a wrapper around Firebase Auth functionality.
class AuthService {
  /// Error service for logging authentication errors.
  final _errorService = ErrorService();
  
  /// Firebase Auth instance for authentication operations.
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;

  /// Gets the currently authenticated user.
  /// 
  /// Returns null if no user is currently signed in.
  User? get currentUser => firebaseAuth.currentUser;

  /// Stream that emits authentication state changes.
  /// 
  /// Emits the current user when authenticated, null when not authenticated.
  Stream<User?> get authStateChanges => firebaseAuth.authStateChanges();

  /// Signs in a user with email and password.
  /// 
  /// Returns a [UserCredential] containing the authenticated user's information.
  /// Throws [FirebaseAuthException] if authentication fails.
  Future<UserCredential> signInWithEmailAndPassword({
    required String email,
    required String password
  }) async {
    return await firebaseAuth.signInWithEmailAndPassword(
        email: email, password: password);
  }

  /// Creates a new user account with email and password.
  /// 
  /// Returns a [UserCredential] containing the new user's information.
  /// Throws [FirebaseAuthException] if account creation fails.
  Future<UserCredential> signUpWithEmailAndPassword({
      required String email, 
      required String password
    }) async {
    return await firebaseAuth.createUserWithEmailAndPassword(
        email: email, password: password);
  }

  /// Signs out the current user.
  /// 
  /// Clears the authentication state and signs out the user from Firebase.
  Future<void> signOut() async {
    await firebaseAuth.signOut();
  }

  /// Sends a password reset email to the specified email address.
  /// 
  /// The user will receive an email with instructions to reset their password.
  /// Throws [FirebaseAuthException] if the email is invalid or other errors occur.
  Future<void> resetPassword(String email) async {
    await firebaseAuth.sendPasswordResetEmail(email: email);
  }

  /// Updates the display name of the current user.
  /// 
  /// Requires a user to be currently authenticated.
  /// Throws if no user is signed in.
  Future<void> updateDisplayName({
    required String displayName,
  }) async {
    await currentUser!.updateDisplayName(displayName);
  }

  /// Deletes the current user's account permanently.
  /// 
  /// Requires re-authentication with the user's current password for security.
  /// This operation cannot be undone.
  /// 
  /// [password] - The user's current password for re-authentication
  /// [email] - The user's email address for re-authentication
  Future<void> deleteAccount({
    required String password,
    required String email,
  }) async {
    // Re-authenticate the user for security
    AuthCredential credential =
        EmailAuthProvider.credential(email: email, password: password);
    await currentUser!.reauthenticateWithCredential(credential);

    // Delete the user account permanently
    await currentUser!.delete();
    await firebaseAuth.signOut();
  }

  /// Resets the user's password after re-authentication.
  /// 
  /// This method allows users to change their password by providing their
  /// current password for security verification.
  /// 
  /// [currentPassword] - The user's current password for verification
  /// [newPassword] - The new password to set
  /// [email] - The user's email address for re-authentication
  Future<void> resetPasswordFromCurrentPassword({
    required String currentPassword,
    required String newPassword,
    required String email,
  }) async {
    // Re-authenticate the user for security
    AuthCredential credential =
        EmailAuthProvider.credential(email: email, password: currentPassword);
    await currentUser!.reauthenticateWithCredential(credential);

    // Update to the new password
    await currentUser!.updatePassword(newPassword);
  }

  /// Ensures Google Sign-In is properly initialized.
  /// 
  /// This method must be called before attempting Google authentication.
  Future<void> ensureInitialized(){
    return GoogleSignInPlatform.instance.init(const InitParameters());
  }

  /// Signs in a user using Google authentication.
  /// 
  /// Handles the complete Google Sign-In flow including platform initialization
  /// and credential exchange with Firebase.
  /// 
  /// Returns a [UserCredential] containing the authenticated user's information.
  /// Throws various exceptions if authentication fails.
  Future<UserCredential> signInWithGoogle() async {
    try {
      await ensureInitialized();
      final AuthenticationResults result = await GoogleSignInPlatform.instance.authenticate(const AuthenticateParameters());
      final String? idToken = result.authenticationTokens.idToken;
      if (idToken == null) {
        throw FirebaseAuthException(
          code: 'ERROR_MISSING_GOOGLE_ID_TOKEN',
          message: 'Missing Google ID Token',
        );
      } else {
        final OAuthCredential credential = GoogleAuthProvider.credential(idToken: idToken);
        UserCredential userCredential = await firebaseAuth.signInWithCredential(credential);
        
        // Return the UserCredential instead of void
        return userCredential;
      }

    } on GoogleSignInException catch (e) {
      _errorService.logError('Google Sign-In error: $e', StackTrace.current);
      rethrow;
    } on FirebaseAuthException catch (e) {
      _errorService.logError('Firebase error during Google Sign-In initialization: $e', StackTrace.current);
      rethrow;
    } catch (e) {
      _errorService.logError('Unknown error during Google Sign-In initialization: $e', StackTrace.current);
      rethrow;
    }
  }

  /// Signs in a user using Apple authentication.
  /// 
  /// TODO: Implement Apple Sign-In functionality
  /// This method is currently a placeholder for future Apple authentication support.
  Future signInWithApple() async {
    // TODO: Implement Apple sign-in
  }
  
}