FacebookLoginButtonAction.swift

func facebookSignInButtonTapped(with sender: LoginView) {
  
        FBSDKLoginManager().logIn(withReadPermissions: ["email"], from: self, handler: { (result, error) in
          
            guard result != nil, !(result?.isCancelled)!, error == nil else { return  FBSDKLoginManager().logOut()}
                    if let accessToken = result?.token.tokenString {
                        let credential = FIRFacebookAuthProvider.credential(withAccessToken: accessToken)
                        FIRAuth.auth()?.signIn(with: credential) { (user, error) in
                            if let error = error {
                                print(error.localizedDescription)
                                let alert = UIAlertController(title: "error", message: "\(error.localizedDescription)", preferredStyle: .alert)
                                let okAction = UIAlertAction(title: "Ok", style: .default, handler: nil)
                                alert.addAction(okAction)
                            }else{
                                DispatchQueue.main.async {
                                    NotificationCenter.default.post(name: .closeLoginVC, object: nil)
                                }
                            }
                        }
                    }
          
        })
        
    }