AuthService.swift

import FirebaseAuth
import GoogleSignIn
import Firebase
import UIKit

class AuthService {
    static let shared = AuthService()

    /// Sign in using Google
    func signInWithGoogle(presentingViewController: UIViewController, completion: @escaping (Bool, Error?) -> Void) {
        guard let clientID = FirebaseApp.app()?.options.clientID else {
            completion(false, NSError(domain: "GoogleSignIn", code: -1, userInfo: [NSLocalizedDescriptionKey: "Missing client ID"]))
            return
        }

        let config = GIDConfiguration(clientID: clientID)
        GIDSignIn.sharedInstance.configuration = config

        GIDSignIn.sharedInstance.signIn(withPresenting: presentingViewController) { result, error in
            if let error = error {
                completion(false, error)
                return
            }

            guard let user = result?.user, let idToken = user.idToken else {
                completion(false, NSError(domain: "GoogleSignIn", code: -1, userInfo: [NSLocalizedDescriptionKey: "Failed to get user ID token"]))
                return
            }

            let credential = GoogleAuthProvider.credential(withIDToken: idToken.tokenString, accessToken: user.accessToken.tokenString)

            Auth.auth().signIn(with: credential) { _, error in
                if let error = error {
                    completion(false, error)
                } else {
                    completion(true, nil)
                }
            }
        }
    }

    /// Sign in using Email/Password
    func signInWithEmail(email: String, password: String, completion: @escaping (Bool, Error?) -> Void) {
        Auth.auth().signIn(withEmail: email, password: password) { _, error in
            if let error = error {
                completion(false, error)
            } else {
                completion(true, nil)
            }
        }
    }

    /// Continue as Guest (Anonymous Sign-in)
    func signInAnonymously(completion: @escaping (Bool, Error?) -> Void) {
        Auth.auth().signInAnonymously { _, error in
            if let error = error {
                completion(false, error)
            } else {
                completion(true, nil)
            }
        }
    }

    /// Sign out user
    func signOut(completion: @escaping (Bool, Error?) -> Void) {
        do {
            try Auth.auth().signOut()
            completion(true, nil)
        } catch let error {
            completion(false, error)
        }
    }
}