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import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var loginTextField: UITextField?
    @IBOutlet weak var passwordTextField: UITextField?
    @IBOutlet weak var loginButton: UIButton?
    
    override func viewDidLoad() {
        super.viewDidLoad()
    
        loginButton?.isEnabled = false
    }
    
    @IBAction func loginChanged(_ sender: UITextField) {
        handleInput(login: sender.text ?? "", password: passwordTextField?.text ?? "")
    }
    
    @IBAction func passwordChanged(_ sender: UITextField) {
        handleInput(login: loginTextField?.text ?? "", password: sender.text ?? "")
    }
    
    func handleInput(login: String, password: String) {
        loginButton?.isEnabled = login.isLoginValid && password.isPasswordValid
    }

}

extension String {
    
    var isLoginValid: Bool {
        return self.count > 0
    }
    
    var isPasswordValid: Bool {
        return self.count > 5
    }
}