class ButtonConcreteBuilder: ButtonBuilder {
    private var product = UIButton()

    ... 생략
    // 텍스트 입력
    func setTitle(_ title: String) -> ButtonBuilder {
        self.product.setTitle(title, for: .normal)
        return self
    }

    // 테두리 적용 (컬러와 폭을 한번에 받아 보다 쉽게 적용)
    func setBolder(color: UIColor, width: CGFloat) -> ButtonBuilder {
        self.product.layer.borderWidth = width
        self.product.layer.borderColor = color.cgColor
        return self
    }

    // 객체 반환
    func build() -> UIButton? {
        return self.product
    }
}

class ButtonDirector {
    static func makeBottomButton() -> UIButton {
        let titleColor = UIColor(red: 1, green: 192/255, blue: 0, alpha: 1)
        let highLightColor = titleColor.withAlphaComponent(0.4)
        let bgColor = UIColor(red: 51/255, green: 59/255, blue: 67/255, alpha: 1)
        let font = UIFont.boldSystemFont(ofSize: 17)
        let radius: CGFloat = 8

        let screenFrame = UIScreen.main.bounds
        let screenSize = screenFrame.size
        let margin: CGFloat = 12.0
        let height: CGFloat = 45.0
        let size = CGSize(width: screenSize.width - (margin * 2), height: height)
        let point = CGPoint(x: margin, y: screenSize.height - height - (margin * 2))
        let frame = CGRect(origin: point, size: size)


      	// 1. Chain을 이용하여 값 셋팅
        let builder = ButtonConcreteBuilder()
            .setBGColor(bgColor)
            .setTitleColor(titleColor)
            .setTitleHighlightedColor(highLightColor)
            .setFont(font)
            .setFrame(frame)
            .setRadius(radius)
            .setTitle("Bottom")

        return builder.build()
    }
}

class ViewController: UIViewController {
		
    ...
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        self.addBottomButton()
    }
    
    private func addBottomButton() {
        let bottomButton = ButtonDirector.makeBottomButton()
        self.view.addSubview(bottomButton)
    }
}