How to make UIButton unclickable after touched one time and hide and unhide button? - swift

I have made a quiz app. 1) I want the buttons with the answers to be unclickable if it is touched one time per question.2) Also i want to hide and unhide the "next question" button everytime the user moves to the next answer. For example Question 1. next question button is hidden --> user touches an answer --> all answer buttons become unclickable ( 1) i want to do this)--> next question button unhidden ( 2) i want to do this).

import UIKit

struct Question {
    var Question: String!
    var Answers: [String]!
    var Answer: Int!

    init(item: [String: Any])
    {
        self.Question = item["Question"] as? String
        self.Answers = item["Answers"] as? [String]
        self.Answer = item["Answer"] as? Int
    }
}

class LittleTestViewController: UIViewController {

    //MARK: Properties
    @IBOutlet weak var questionLabel: UILabel!
    @IBOutlet var buttons: [UIButton]!
    @IBOutlet weak var Next: UIButton!

    var Questions = [Question]()
    var QNumber = Int()
    var answerNumber = Int()
    var score = Int()

    override func viewDidLoad() {
        super.viewDidLoad()
        Hide()
        jsonParsingQuestionsFile()
        pickQuestion()
    }

    func jsonParsingQuestionsFile ()
    {
        if let path = Bundle.main.path(forResource: "data", ofType: "json")
        {
            if let array = (try? JSONSerialization.jsonObject(with: Data(contentsOf: URL(fileURLWithPath: path), options: .mappedIfSafe), options: JSONSerialization.ReadingOptions.allowFragments)) as? [[String : Any]]
            {
                for item in array
                {   
                    self.Questions.append(Question(item: item))
                }
            }
        }
    }

    func pickQuestion ()
    {

        if Questions.count > 0 {
            QNumber = 0

            questionLabel.text = Questions[QNumber].Question

            answerNumber = Questions[QNumber].Answer

            for i in 0..<buttons.count{
                buttons[i].setTitle(Questions[QNumber].Answers[i], for: UIControlState.normal)
            }
            Questions.remove(at: QNumber)
        }
        else
        {
           let alert = UIAlertController(title: "Σκόρ", message: "Απάντησες σωστάς τις \(score) ερωτήσεις από τις 3", preferredStyle: UIAlertControllerStyle.alert)
            alert.addAction(UIAlertAction(title: "Μενού", style: UIAlertActionStyle.default, handler: { action in
                self.navigationController?.popToRootViewController(animated: true)
            }))
            self.present(alert, animated: true, completion: nil)
        }
    }

    func Hide()
    {
        Next.isHidden = true
    }

    func Unhide()
    {
        Next.isHidden = false
    }

    @IBAction func bt1(_ sender: UIButton) {
        Unhide()
        if answerNumber == 0 {
            sender.backgroundColor = UIColor.green
            score+=1
        }
        else
        {
            sender.backgroundColor = UIColor.red
        }
    }
    @IBAction func btn2(_ sender: UIButton) {
        Unhide()
        if answerNumber == 1 {
            sender.backgroundColor = UIColor.green
            score+=1
        }
        else
        {
            sender.backgroundColor = UIColor.red
        }
    }
    @IBAction func btn3(_ sender: UIButton) {
        Unhide()
        if answerNumber == 2 {
            sender.backgroundColor = UIColor.green
            score+=1
        }
        else
        {
            sender.backgroundColor = UIColor.red
        }
    }
    @IBAction func btn4(_ sender: UIButton) {
        Unhide()
        if answerNumber == 3 {
            sender.backgroundColor = UIColor.green
            score+=1
        }
        else
        {
            sender.backgroundColor = UIColor.red
        }
    }

    @IBAction func Next(_ sender: Any)
    {
        pickQuestion()
    }

}