//
//  RDReaderView.swift
//  RDReaderDemo
//
//  Created by yangsq on 2021/8/6.
//

import UIKit


@objc public protocol RDReaderDataSource: NSObjectProtocol {
    func pageCountOfReaderView(readerView: RDReaderView) -> Int
    func pageContentView(readerView: RDReaderView, pageNum: Int, containerView: UIView?) -> UIView
    func pageIdentifier(readerView: RDReaderView, pageNum: Int) -> String?
    @objc optional func topToolView(readerView: RDReaderView) -> UIView?
    @objc optional func bottomToolView(readerView: RDReaderView) -> UIView?
}

@objc public protocol RDReaderDelegate: NSObjectProtocol {
    func pageNum(readerView: RDReaderView, pageNum: Int)
    /// 横竖屏切换时回调，可在此重新分页
    @objc optional func readerViewOrientationWillChange(readerView: RDReaderView, isLandscape: Bool)
}

extension RDReaderView {
   public enum DisplayType {
        case pageCurl
        case horizontalScroll
        case verticalScroll
    }
    
    /// 翻页方向
    public enum PageDirection {
        /// 从左往右翻页（默认，适用于中文/英文书籍）
        case leftToRight
        /// 从右往左翻页（适用于日文漫画等）
        case rightToLeft
    }
}

public class RDReaderView: UIView {
    
    enum TapEvent {
        case none, left, center, right
    }
    
    private lazy var pageViewController: UIPageViewController = {
        let pageVC = UIPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal, options: nil)
        pageVC.delegate = self
        pageVC.dataSource = self
        return pageVC
    }()
    
    private lazy var layout: RDReaderFlowLayout = {
        let layout = RDReaderFlowLayout(displayType: .horizontalScroll)
        layout.dataSource = self
        layout.delegate = self
        return layout
    }()
    
    private lazy var collectionView: UICollectionView = {
        
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.backgroundColor = UIColor.clear
        return collectionView
    }()
    
    public var currentPage: Int = -1 {
        didSet {
            if let delegate = delegate, currentPage != oldValue, delegate.responds(to: #selector(RDReaderDelegate.pageNum(readerView:pageNum:))) {
                delegate.pageNum(readerView: self, pageNum: currentPage)
            }
        }
    }
    
    private(set) lazy var tapGestureRecognizer: UITapGestureRecognizer = {
        let tap = UITapGestureRecognizer(target: self, action: #selector(tapAction(tap:)))
        return tap
    }()
    
    private var tapEvent: TapEvent = .none {
        didSet {
            let isRTL = pageDirection == .rightToLeft
            switch tapEvent {
            case .left:
                if currentDisplayType != .pageCurl {
                    if isRTL { goNextPage() } else { goPreviousPage() }
                }
            case .right:
                if currentDisplayType != .pageCurl {
                    if isRTL { goPreviousPage() } else { goNextPage() }
                }
            case .center:
                tapCenter()
            default:
                break
            }
        }
    }
    
    private func goNextPage() {
        let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
        if pagesPerScreen > 1 {
            if let target = adjacentDualPage(from: currentPage, forward: true) {
                transitionToPage(pageNum: target, animated: true)
            }
        } else if currentPage + 1 < totalPages {
            transitionToPage(pageNum: currentPage + 1, animated: true)
        }
    }
    
    private func goPreviousPage() {
        if pagesPerScreen > 1 {
            if let target = adjacentDualPage(from: currentPage, forward: false) {
                transitionToPage(pageNum: target, animated: true)
            }
        } else if currentPage - 1 >= 0 {
            transitionToPage(pageNum: currentPage - 1, animated: true)
        }
    }
    
    public weak var dataSource: RDReaderDataSource? = nil
    public weak var delegate: RDReaderDelegate? = nil
    public var currentDisplayType: RDReaderView.DisplayType = .pageCurl
    public var toolViewAnimationDuration: TimeInterval = 0.3
    /// 是否启用横屏双页显示
    public var landscapeDualPageEnabled: Bool = false
    /// 翻页方向，默认从左往右（.leftToRight）
    public var pageDirection: RDReaderView.PageDirection = .leftToRight
    /// 横屏双页模式下，封面页的索引。设置后该页在横屏时独占一屏，后续页面两两配对。
    /// 设为 nil 表示没有封面页（所有页面正常两两配对）。
    public var coverPageIndex: Int? = nil
    
    /// 是否启用了封面页独占
    private var hasCoverPage: Bool {
        return coverPageIndex != nil
    }
    
    /// 当前是否横屏
    private var isLandscape: Bool {
        return bounds.width > bounds.height
    }
    
    /// 每屏显示的页数
    public var pagesPerScreen: Int {
        if !landscapeDualPageEnabled { return 1 }
        if currentDisplayType == .verticalScroll { return 1 }
        return isLandscape ? 2 : 1
    }
    
    /// 判断某页在横屏双页模式下是否独占一屏（封面页）
    /// - Parameter pageNum: 页码
    /// - Returns: 是否独占一屏
    public func isFullScreenPage(_ pageNum: Int) -> Bool {
        guard landscapeDualPageEnabled, isLandscape, let coverIndex = coverPageIndex else { return false }
        return pageNum == coverIndex
    }
    
    /// 根据逻辑页码计算横屏双页模式下的配对信息
    /// 封面页独占一屏，后续页面两两配对
    /// - Parameter pageNum: 逻辑页码
    /// - Returns: (左页码, 右页码(可选))
    private func dualPagePair(for pageNum: Int) -> (left: Int, right: Int?) {
        let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
        if let coverIndex = coverPageIndex {
            if pageNum == coverIndex {
                // 封面页独占一屏
                return (coverIndex, nil)
            }
            // 封面之后的页面：偏移1后两两配对
            // 例如封面是0页，则 1+2, 3+4, 5+6...
            let adjustedIndex = pageNum - (coverIndex + 1) // 跳过封面后的偏移
            let pairStart = coverIndex + 1 + (adjustedIndex / 2) * 2
            let left = pairStart
            let right = pairStart + 1 < totalPages ? pairStart + 1 : nil
            return (left, right)
        } else {
            // 无封面页：正常两两配对 0+1, 2+3, 4+5...
            let left = (pageNum / 2) * 2
            let right = left + 1 < totalPages ? left + 1 : nil
            return (left, right)
        }
    }
    
    /// 计算横屏双页下，某页往前/后翻一屏后的起始页码
    /// - Parameters:
    ///   - pageNum: 当前页码
    ///   - forward: 是否向后翻
    /// - Returns: 目标页码，nil 表示到头了
    private func adjacentDualPage(from pageNum: Int, forward: Bool) -> Int? {
        let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
        let pair = dualPagePair(for: pageNum)
        if forward {
            let nextStart = (pair.right ?? pair.left) + 1
            return nextStart < totalPages ? nextStart : nil
        } else {
            let prevEnd = pair.left - 1
            guard prevEnd >= 0 else { return nil }
            return dualPagePair(for: prevEnd).left
        }
    }
    
    private var previousIsLandscape: Bool?
    
    private var contentViews = [String : UIView.Type]()
    private var willPreviousTransitionToViewController: UIViewController? = nil
    private var willNextTransitionToViewController: UIViewController? = nil
    private var willTransitionToViewController: UIViewController? = nil
    private var topToolView: UIView?
    private var bottomToolView: UIView?
    private var isShowToolView: Bool = false
    private var isTransitioning: Bool = false
    private var didBuildUI = false
    
    /// 用于 pageCurl 双页模式下封面页旁边的空白页
    static let blankPageNum = Int.max
    /// 用于 pageCurl 双页模式下末尾不成对页旁边的空白页
    static let blankEndPageNum = Int.max - 1

    override init(frame: CGRect) {
        super.init(frame: frame)
    }
    
    public override func layoutSubviews() {
        super.layoutSubviews()
        guard bounds.width > 0, bounds.height > 0 else { return }
        let nowLandscape = isLandscape
        if let prev = previousIsLandscape, prev != nowLandscape {
            previousIsLandscape = nowLandscape
            // 延迟到下一个 RunLoop 执行，避免在 layoutSubviews 中嵌套触发 reloadData/layoutIfNeeded
            // 造成 collectionView 中间态尺寸不一致的问题
            DispatchQueue.main.async { [weak self] in
                guard let self = self else { return }
                self.orientationChanged(isNowLandscape: nowLandscape)
            }
        } else if previousIsLandscape == nil {
            previousIsLandscape = nowLandscape
            layout.isLandscapeDualPage = landscapeDualPageEnabled && nowLandscape
        }
    }
    
    /// 横竖屏切换处理
    /// - Parameter isNowLandscape: 当前是否为横屏
    private func orientationChanged(isNowLandscape: Bool) {
        let savedPage = max(0, currentPage)
        // 1. 通知代理方向变化。正文级重分页由上层控制器统一接管，这里只保留容器级刷新钩子。
        delegate?.readerViewOrientationWillChange?(readerView: self, isLandscape: isNowLandscape)
        // 2. 更新布局的横屏双页标记
        layout.isLandscapeDualPage = landscapeDualPageEnabled && isNowLandscape
        layout.coverPageIndex = coverPageIndex
        
        switch currentDisplayType {
        case .pageCurl:
            // 仿真翻页：通过 spineLocation 原生支持双页，需要重建 PageViewController
            rebuildPageViewController()
            transitionToPage(pageNum: savedPage)
        default:
            // 滚动模式：禁用动画防止旋转过渡中出现尺寸抖动
            UIView.performWithoutAnimation {
                // 强制使布局完全失效并重新计算
                collectionView.collectionViewLayout.invalidateLayout()
                collectionView.reloadData()
                collectionView.layoutIfNeeded()
                // 3. 根据保存的页码恢复滚动位置
                let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
                let safePage = min(savedPage, max(0, totalPages - 1))
                let targetOffset = layout.currentContentOffset(count: safePage)
                collectionView.setContentOffset(targetOffset, animated: false)
            }
        }
    }
    
    /// 创建带指定 spine 位置的 UIPageViewController
    /// - Parameter isDualPage: 是否双页模式（横屏时书脊在中间：.mid）
    private func createPageViewController(isDualPage: Bool) -> UIPageViewController {
        let options: [UIPageViewController.OptionsKey: Any]?
        if isDualPage {
            options = [.spineLocation: NSNumber(value: UIPageViewController.SpineLocation.mid.rawValue)]
        } else {
            options = nil
        }
        let pageVC = UIPageViewController(transitionStyle: .pageCurl, navigationOrientation: .horizontal, options: options)
        pageVC.delegate = self
        pageVC.dataSource = self
        pageVC.isDoubleSided = isDualPage
        return pageVC
    }
    
    /// 重建 UIPageViewController。横竖屏切换时需要重建，因为 spineLocation 只能在初始化时设置
    private func rebuildPageViewController() {
        detachPageViewControllerIfNeeded()
        
        let isDualPage = landscapeDualPageEnabled && isLandscape
        let pageVC = createPageViewController(isDualPage: isDualPage)
        pageViewController = pageVC
        attachPageViewControllerIfNeeded()
    }
    
    public override func didMoveToSuperview() {
        super.didMoveToSuperview()

        if superview != nil {
            makeUI()
        }
    }

    private func attachPageViewControllerIfNeeded() {
        guard let parentViewController = self.ss_superViewController else { return }

        var didAddToParent = false
        if pageViewController.parent !== parentViewController {
            if pageViewController.parent != nil {
                pageViewController.willMove(toParent: nil)
                pageViewController.view.removeFromSuperview()
                pageViewController.removeFromParent()
            }
            parentViewController.addChild(pageViewController)
            didAddToParent = true
        }

        pageViewController.view.frame = CGRect(x: 0, y: 0, width: frame.width, height: frame.height)
        pageViewController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        if pageViewController.view.superview !== self {
            insertSubview(pageViewController.view, at: 0)
        }

        if didAddToParent {
            pageViewController.didMove(toParent: parentViewController)
        }
    }

    private func detachPageViewControllerIfNeeded() {
        if pageViewController.parent != nil {
            pageViewController.willMove(toParent: nil)
        }
        pageViewController.view.removeFromSuperview()
        if pageViewController.parent != nil {
            pageViewController.removeFromParent()
        }
    }
    
    private func makeUI() {
        guard !didBuildUI else {
            if currentDisplayType == .pageCurl {
                attachPageViewControllerIfNeeded()
            }
            return
        }
        didBuildUI = true

        collectionView.dataSource = self
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: NSStringFromClass(UICollectionViewCell.self))
        collectionView.frame = CGRect(x: 0, y: 0, width: frame.width, height: frame.height)
        collectionView.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        if currentDisplayType == .pageCurl {
            attachPageViewControllerIfNeeded()
        }
        
        addGestureRecognizer(tapGestureRecognizer)
        // 不取消底层触摸事件，确保工具栏按钮（返回等）的 touchUpInside 能正常触发
        tapGestureRecognizer.cancelsTouchesInView = false

    }
    
    @objc private func tapAction(tap: UITapGestureRecognizer) {
        let point = tap.location(in: tap.view)
        if isShowToolView {
            let hitView = hitTest(point, with: nil)
            if let top = topToolView, isHitView(hitView, inside: top, point: point) { return }
            if let bottom = bottomToolView, isHitView(hitView, inside: bottom, point: point) { return }
        }
        let viewFrame = tap.view!.frame
        let leftFrame = CGRect(x: 0, y: 0, width: viewFrame.width / 3, height: viewFrame.height)
        let centerFrame = CGRect(x: viewFrame.width / 3, y: 0, width: viewFrame.width / 3, height: viewFrame.height)
        let rightFrame = CGRect(x: viewFrame.width * 2 / 3, y: 0, width: viewFrame.width / 3, height: viewFrame.height)
        if leftFrame.contains(point) {
            if isShowToolView {
                tapEvent = .center
            } else {
                tapEvent = .left
            }
        }
        
        if centerFrame.contains(point) {
            tapEvent = .center
        }
        
        if rightFrame.contains(point) {
            if isShowToolView {
                tapEvent = .center
            } else {
                tapEvent = .right
            }
        }
    }
    
    private func tapCenter() {
        isShowToolView = !isShowToolView
        if isShowToolView {
            if let topToolView = topToolView {
                addSubview(topToolView)
                topToolView.translatesAutoresizingMaskIntoConstraints = false
                NSLayoutConstraint.activate([
                    topToolView.leadingAnchor.constraint(equalTo: leadingAnchor),
                    topToolView.trailingAnchor.constraint(equalTo: trailingAnchor),
                    topToolView.topAnchor.constraint(equalTo: topAnchor)
                ])
                layoutIfNeeded()
                topToolView.transform = CGAffineTransform(translationX: 0, y: -topToolView.bounds.height)
                UIView.animate(withDuration: toolViewAnimationDuration) {
                    topToolView.transform = .identity
                }
            }

            if let bottomToolView = bottomToolView {
                addSubview(bottomToolView)
                bottomToolView.translatesAutoresizingMaskIntoConstraints = false
                NSLayoutConstraint.activate([
                    bottomToolView.leadingAnchor.constraint(equalTo: leadingAnchor),
                    bottomToolView.trailingAnchor.constraint(equalTo: trailingAnchor),
                    bottomToolView.bottomAnchor.constraint(equalTo: bottomAnchor)
                ])
                layoutIfNeeded()
                bottomToolView.transform = CGAffineTransform(translationX: 0, y: bottomToolView.bounds.height)
                UIView.animate(withDuration: toolViewAnimationDuration) {
                    bottomToolView.transform = .identity
                }
            }

            collectionView.isUserInteractionEnabled = false
            pageViewController.view.isUserInteractionEnabled = false
        } else {
            if let topToolView = topToolView {
                UIView.animate(withDuration: toolViewAnimationDuration, animations: {
                    topToolView.transform = CGAffineTransform(translationX: 0, y: -topToolView.bounds.height)
                }) { _ in
                    topToolView.removeFromSuperview()
                }
            }

            if let bottomToolView = bottomToolView {
                UIView.animate(withDuration: toolViewAnimationDuration, animations: {
                    bottomToolView.transform = CGAffineTransform(translationX: 0, y: bottomToolView.bounds.height)
                }) { _ in
                    bottomToolView.removeFromSuperview()
                }
            }

            collectionView.isUserInteractionEnabled = true
            pageViewController.view.isUserInteractionEnabled = true
        }
    }

    private func isHitView(_ hitView: UIView?, inside toolView: UIView, point: CGPoint) -> Bool {
        if toolView.frame.contains(point) {
            return true
        }

        guard let hitView else { return false }
        return hitView === toolView || hitView.isDescendant(of: toolView)
    }
    
    /// 切换翻页模式（仿真/水平滚动/上下滚动）
    /// 会重建底层视图（PageViewController 或 CollectionView），并恢复到当前页
    public func switchReaderDisplayType(_ displayType: RDReaderView.DisplayType) {
        self.currentDisplayType = displayType
        if currentPage == -1 {
            currentPage = 0
        }
        // 同步横屏双页标记到布局
        layout.isLandscapeDualPage = landscapeDualPageEnabled && isLandscape
        layout.coverPageIndex = coverPageIndex
        switch displayType {
        case .pageCurl:
            self.collectionView.removeFromSuperview()
            self.collectionView.transform = .identity
            attachPageViewControllerIfNeeded()
            rebuildPageViewController()
            transitionToPage(pageNum: currentPage)
        default:
            detachPageViewControllerIfNeeded()
            // RTL 水平模式翻转 collectionView
            if pageDirection == .rightToLeft && displayType != .verticalScroll {
                collectionView.transform = CGAffineTransform(scaleX: -1, y: 1)
            } else {
                collectionView.transform = .identity
            }
            // 确保 collectionView frame 正确后再触发布局计算
            collectionView.frame = CGRect(x: 0, y: 0, width: frame.width, height: frame.height)
            insertSubview(self.collectionView, at: 0)
            layout.displayType = displayType
            transitionToPage(pageNum: currentPage)
        }
    }
    
    /// 跳转到指定页码
    /// - Parameters:
    ///   - pageNum: 目标页码（item 索引）
    ///   - animated: 是否动画过渡
    public func transitionToPage(pageNum: Int, animated: Bool = false) {
        switch currentDisplayType {
        case .pageCurl:
            let isDualPage = landscapeDualPageEnabled && isLandscape
            // RTL 时动画方向需要反转
            let direction: UIPageViewController.NavigationDirection
            if pageDirection == .rightToLeft {
                direction = pageNum > currentPage ? .reverse : .forward
            } else {
                direction = pageNum > currentPage ? .forward : .reverse
            }
            if isDualPage {
                let pair = dualPagePair(for: pageNum)
                let leftContent = dataSource?.pageContentView(readerView: self, pageNum: pair.left, containerView: nil)
                let leftVC = RDReaderPageChildViewController(contentView: leftContent, pageNum: pair.left)
                if let rightPage = pair.right {
                    let rightContent = dataSource?.pageContentView(readerView: self, pageNum: rightPage, containerView: nil)
                    let rightVC = RDReaderPageChildViewController(contentView: rightContent, pageNum: rightPage)
                    pageViewController.setViewControllers([leftVC, rightVC], direction: animated ? direction : .forward, animated: animated, completion: nil)
                } else {
                    // 封面页独占或奇数最后一页：右侧放空白页
                    let blankNum = isFullScreenPage(pair.left) ? RDReaderView.blankPageNum : RDReaderView.blankEndPageNum
                    let emptyVC = RDReaderPageChildViewController(contentView: UIView(), pageNum: blankNum)
                    pageViewController.setViewControllers([leftVC, emptyVC], direction: animated ? direction : .forward, animated: animated, completion: nil)
                }
                currentPage = pair.left
            } else {
                let contentView = dataSource?.pageContentView(readerView: self, pageNum: pageNum, containerView: nil)
                let vc = RDReaderPageChildViewController(contentView: contentView, pageNum: pageNum)
                pageViewController.setViewControllers([vc], direction: animated ? direction : .forward, animated: animated, completion: nil)
                currentPage = pageNum
            }
        default:
            collectionView.reloadData()
            collectionView.layoutIfNeeded()
            collectionView.setContentOffset(layout.currentContentOffset(count: pageNum), animated: animated)
        }
    }
    
    public func reloadData() {
        switchReaderDisplayType(currentDisplayType)
        topToolView = self.dataSource?.topToolView?(readerView: self)
        bottomToolView = self.dataSource?.bottomToolView?(readerView: self)
    }
    
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}



extension RDReaderView: UIPageViewControllerDataSource, UIPageViewControllerDelegate {
    
    private func makeSinglePageChildVC(for pageNum: Int) -> RDReaderPageChildViewController {
        if pageNum == RDReaderView.blankPageNum || pageNum == RDReaderView.blankEndPageNum {
            return RDReaderPageChildViewController(contentView: UIView(), pageNum: pageNum)
        }
        let contentView = dataSource?.pageContentView(readerView: self, pageNum: pageNum, containerView: nil)
        return RDReaderPageChildViewController(contentView: contentView, pageNum: pageNum)
    }
    
    /// 计算某页的"下一页"页码（考虑封面页插入空白页）
    private func nextPageNum(after pageNum: Int, isDualPage: Bool) -> Int? {
        let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
        
        // 末尾空白页之后没有更多页
        if pageNum == RDReaderView.blankEndPageNum {
            return nil
        }
        
        if isDualPage, let coverIndex = coverPageIndex {
            if pageNum == coverIndex {
                return RDReaderView.blankPageNum
            }
            if pageNum == RDReaderView.blankPageNum {
                let firstContent = coverIndex + 1
                return firstContent < totalPages ? firstContent : nil
            }
        }
        
        let next = pageNum + 1
        if next < totalPages {
            return next
        }
        
        // pageNum 是最后一页，检查在双页模式下是否需要空白页配对
        if isDualPage {
            if let coverIndex = coverPageIndex {
                // 有封面时：封面之后的页面两两配对，偶数偏移=左页需要配对
                let adjustedIndex = pageNum - (coverIndex + 1)
                if adjustedIndex >= 0 && adjustedIndex % 2 == 0 {
                    return RDReaderView.blankEndPageNum
                }
            } else {
                // 无封面：偶数索引=左页需要配对
                if pageNum % 2 == 0 {
                    return RDReaderView.blankEndPageNum
                }
            }
        }
        return nil
    }
    
    /// 计算某页的"上一页"页码（考虑封面页插入空白页）
    private func prevPageNum(before pageNum: Int, isDualPage: Bool) -> Int? {
        // 末尾空白页的前一页是最后一个真实页
        if pageNum == RDReaderView.blankEndPageNum {
            let totalPages = dataSource?.pageCountOfReaderView(readerView: self) ?? 0
            return totalPages > 0 ? totalPages - 1 : nil
        }
        if isDualPage, let coverIndex = coverPageIndex {
            if pageNum == RDReaderView.blankPageNum {
                return coverIndex
            }
            if pageNum == coverIndex + 1 {
                return RDReaderView.blankPageNum
            }
        }
        let prev = pageNum - 1
        return prev >= 0 ? prev : nil
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let vc = viewController as? RDReaderPageChildViewController else { return nil }
        let isDualPage = landscapeDualPageEnabled && isLandscape
        let isRTL = pageDirection == .rightToLeft
        
        // RTL 时 before/after 语义互换：before（向右翻）= 下一页
        let targetNum = isRTL
            ? nextPageNum(after: vc.pageNum, isDualPage: isDualPage)
            : prevPageNum(before: vc.pageNum, isDualPage: isDualPage)
        
        guard let num = targetNum else { return nil }
        let targetVC = makeSinglePageChildVC(for: num)
        willPreviousTransitionToViewController = targetVC
        return targetVC
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let vc = viewController as? RDReaderPageChildViewController else { return nil }
        let isDualPage = landscapeDualPageEnabled && isLandscape
        let isRTL = pageDirection == .rightToLeft
        
        let targetNum = isRTL
            ? prevPageNum(before: vc.pageNum, isDualPage: isDualPage)
            : nextPageNum(after: vc.pageNum, isDualPage: isDualPage)
        
        guard let num = targetNum else { return nil }
        let targetVC = makeSinglePageChildVC(for: num)
        willNextTransitionToViewController = targetVC
        return targetVC
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if completed, let firstVC = pageViewController.viewControllers?.first as? RDReaderPageChildViewController {
            let pn = firstVC.pageNum
            if pn != RDReaderView.blankPageNum && pn != RDReaderView.blankEndPageNum {
                currentPage = pn
            }
        }
    }
    
    public func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
        willTransitionToViewController = pendingViewControllers.first
    }
    
}

extension RDReaderView: UICollectionViewDataSource, RDReaderFlowLayoutDelegate, RDReaderFlowLayoutDataSoure {
    public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
       
        
        if let identifer = self.dataSource?.pageIdentifier(readerView: self, pageNum: indexPath.row) {
            
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifer, for: IndexPath(item: indexPath.row, section: 0)) as! RDReaderContentCell
            let conttainerView = self.dataSource?.pageContentView(readerView: self, pageNum: indexPath.row, containerView: cell.containerView)
            if let conttainerView = conttainerView {
                cell.containerView = conttainerView
            }
            // RTL 水平模式：翻转 cell 内容使文字方向正常（collectionView 已整体翻转）
            if pageDirection == .rightToLeft && currentDisplayType != .verticalScroll {
                cell.contentView.transform = CGAffineTransform(scaleX: -1, y: 1)
            } else {
                cell.contentView.transform = .identity
            }
            return cell
        }
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: NSStringFromClass(UICollectionViewCell.self), for: indexPath)
     
        return cell
    }
    
    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.dataSource?.pageCountOfReaderView(readerView: self) ?? 0
    }
    
    public func pageNum(flowLayout: RDReaderFlowLayout, pageIndex: Int) {
        currentPage = pageIndex
        
    }
    
    public func heigtOfVerticalScrollPage(flowLayout: RDReaderFlowLayout, pageIndex: Int) -> CGFloat? {
        return nil
    }
}

extension RDReaderView {
    public func register(contentView: UIView.Type, contentViewWithReuseIdentifier identifier: String) {
        contentViews[identifier] = contentView
        collectionView.register(RDReaderContentCell.self, forCellWithReuseIdentifier: identifier)
    }
    
    
    public func dequeueReusableContentView(withReuseIdentifier identifier: String, for pageNum: Int) -> UIView {
        if self.currentDisplayType != .pageCurl, let cell = self.collectionView.cellForItem(at: IndexPath(row: pageNum, section: 0)) as? RDReaderContentCell, let containerView = cell.containerView {
            return containerView
        }
        let contentViewClass = contentViews[identifier]
        assert(contentViewClass != nil, "请调用register(contentView：contentViewWithReuseIdentifier：）")
        var contentView = contentViewClass!.init()
        return contentView
    }
    
    public func pageContentView(pageNum: Int) -> UIView? {
        if currentDisplayType  == .pageCurl {
          return  (self.pageViewController.viewControllers?.first as? RDReaderPageChildViewController)?.contentView
        } else {
            let cell = collectionView.cellForItem(at: IndexPath(item: pageNum, section: 0)) as? RDReaderContentCell
            return cell?.containerView
        }
    }
}

private var cellViewKey: Int8 = 0
extension UIView {
    var ss_superViewController: UIViewController?  {
        var next = self.next
        while next != nil {
            if next is UIViewController {
                return next as? UIViewController
            } else {
                next = next!.next
            }
        }
        return nil
    }
    
}