Chain of Responsibility to handle errors on iOS application

ChainResponsibility.playground.swift

import UIKit

class AppDelegate {
    var window: UIWindow?
}

//Chain of Resposability: Handler
protocol ErrorHandler {
    var errorHandlerSuccessor: ErrorHandler? {get}
    func handleError(error: Error)
}

//Chain of Resposability: ConcreteHandler1
extension AppDelegate: ErrorHandler {
    //this is the most generalist handler 
    var errorHandlerSuccessor: ErrorHandler? { return nil }
    func handleError(error: Error) {
        let alert =  UIAlertController(title: "General Error", message: error.localizedDescription, preferredStyle: UIAlertControllerStyle.alert)

        window?.rootViewController?.present(alert, animated: true, completion: nil)
    }
}

extension UIViewController: ErrorHandler {
    var errorHandlerSuccessor: ErrorHandler? {
        return parent ?? (UIApplication.shared.delegate as? AppDelegate)
    }
    func handleError(error: Error) {
        //send request to successor by default
        errorHandlerSuccessor?.handleError(error: error)
    }
}

class LoginVC: UIViewController {
    var login: (((Error?)->Void) -> Void)!
    var errorLabel = UILabel()

    func didClickOKButton() {
        login() { error in
            if let error = error {
                //Chain of Resposability: Client
                handleError(error: error)
                return
            }
        }
    }
}

//Chain of Resposability: ConcreteHandler2
extension LoginVC {
    enum Error: Swift.Error {
        case invalidCredentials
    }

    override func handleError(error: Swift.Error) {
        guard let loginError = error as? Error else {
            errorHandlerSuccessor?.handleError(error: error)
            return
        }

        switch loginError {
        case .invalidCredentials:
            errorLabel.isHidden = false
            errorLabel.text = "Invalid credentials."
        }

    }
}