import UIKit

class PageViewController: UIViewController,UIScrollViewDelegate {

    var scrollView = UIScrollView()

    var pageControl = UIPageControl()

    var isPageControlUse = false //新增一個狀態，用來標記頁面的滑動狀態

    override func viewDidLoad() {

        super.viewDidLoad()

        var rect = UIScreen.main.bounds

        let width :CGFloat = UIScreen.main.bounds.width

        let height : CGFloat = UIScreen.main.bounds.height

        scrollView.frame = rect

        scrollView.isPagingEnabled = true //設定按頁顯示

        scrollView.contentSize = CGSize(width: width * 2, height: height)

        scrollView.backgroundColor = UIColor.black

        scrollView.delegate = self

        let pcHei : CGFloat = 50.0

        let pcRect = CGRect(x: 0, y: height - pcHei, width: width, height: pcHei)

        pageControl.frame = pcRect

        pageControl.numberOfPages = 2

        pageControl.currentPage = 0

        pageControl.backgroundColor = UIColor.gray

        pageControl.addTarget(self, action: #selector(pageControlDidChange(sender:)), for: UIControl.Event.valueChanged)

        let firstVC = FirstViewController()

        rect.origin.x = 0.0

        firstVC.view.frame = rect

        let secondVC = SecondViewController()

        rect.origin.x = rect.size.width

        secondVC.view.frame = rect

        scrollView.addSubview(firstVC.view)

        scrollView.addSubview(secondVC.view)

        self.view.addSubview(scrollView)

        self.view.addSubview(pageControl)

    }

//    pageControl點選事件

    @objc private func pageControlDidChange(sender:AnyObject){

        let crtPage = (CGFloat)(pageControl.currentPage)

        var frame = scrollView.frame

        frame.origin.x = frame.size.width * crtPage

        frame.origin.y = 0

        scrollView.scrollRectToVisible(frame, animated: true)

        isPageControlUse = true

    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {

//        如果是通過頁面控制器物件切換頁面，則不執行後面的程式碼

        if(!isPageControlUse){

            let pageWith = scrollView.frame.size.width

            let page = floor((scrollView.contentOffset.x - pageWith/2)/pageWith)//-1~0

            pageControl.currentPage = Int(page + 1)

        }

    }

//    Decelerating停止減速

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {

        isPageControlUse = false;

    }

 }