UIPageControl with designated dots size.

class PageContol: UIPageControl {

    /// 선택 dot 크기 정의
    private var currentSize: CGSize {
        return CGSize(width: 17.5, height: 7)
    }
    /// 기본 dot 크기 정의
    private var defaultSize: CGSize {
        return CGSize(width: 7, height: 7)
    }
    /// 기본 dots itemSpace 정의
    private var dotSpace: CGFloat {
        return 9
    }

    // Constraint 처리
    private var consts = [NSLayoutConstraint]()
    private lazy var deactivateConsts = { [unowned self] in
        self.subviews.forEach {
            $0.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.deactivate($0.constraints)
        }
        self.consts.removeAll()
    }
    private lazy var activateConsts = { [unowned self] in
        NSLayoutConstraint.activate(self.consts)
        self.consts.removeAll()
    }

    override var currentPage: Int {
        didSet {
            // 1. Deactivate constraints.
            deactivateConsts()
            // 2. 1개 또는 복수 일때의 분기 및 constraints 처리.
            switch numberOfPages {
            case 1: onePage()
            default: severalPage()
            }
            // 3. Activate constraints.
            activateConsts()
        }
    }

    /// Dot가 1개일때의 constraints 처리.
    private func onePage() {
        guard let dotView = subviews.first else {return}
        addSizeConsts(currentSize, to: dotView)
        consts.append(dotView.centerXAnchor.constraint(equalTo: centerXAnchor))
        consts.append(dotView.centerYAnchor.constraint(equalTo: centerYAnchor))
    }

    /// Dot가 복수 일때의 constraints 처리.
    private func severalPage() {
        for (index, dotView) in subviews.enumerated() {
            // 1. Vertical 중앙 정렬
            consts.append(dotView.centerYAnchor.constraint(equalTo: centerYAnchor))

            // 2. 선택 및 기본 dots에 대한 size 처리
            if index == currentPage {
                addSizeConsts(currentSize, to: dotView)
            } else {
                addSizeConsts(defaultSize, to: dotView)
            }

            // 3. Dots간 일정거리 유지 처리
            if index == 0 { // 가장 왼쪽
                consts.append(dotView.leadingAnchor.constraint(equalTo: leadingAnchor))
            } else if index == (subviews.count - 1) { // 가장 오른쪽
                consts.append(dotView.leadingAnchor.constraint(equalTo: subviews[index - 1].trailingAnchor,
                                                               constant: dotSpace))
                consts.append(dotView.trailingAnchor.constraint(equalTo: trailingAnchor))
            } else { // 중간
                consts.append(dotView.leadingAnchor.constraint(equalTo: subviews[index - 1].trailingAnchor,
                                                               constant: dotSpace))
            }
        }
    }

    /// 해당 size로 sizeAnchor를 처리한다.
    private func addSizeConsts(_ size: CGSize, to view: UIView) {
        consts.append(view.widthAnchor.constraint(equalToConstant: size.width))
        consts.append(view.heightAnchor.constraint(equalToConstant: size.height))
    }

}