import UIKit

/// 页面创建、缩放状态和点击分区。与 EPUB 的 `RDEpubReaderView+ContentAccess`
/// 及 Paging 模块保持同一职责边界。
extension RDPDFReaderView {
    func makePageView(for page: Int) -> UIView {
        if usesLandscapeSpread {
            let left = dataSource?.pageContentView(readerView: self, pageNum: page) ?? UIView()
            left.tag = page
            let next = page + 1
            let right: UIView?
            if next < pageCount() {
                let view = dataSource?.pageContentView(readerView: self, pageNum: next) ?? UIView()
                view.tag = next
                right = view
            } else {
                right = nil
            }
            let spread = RDPDFReaderPageSpreadView(leftPage: left, rightPage: right)
            spread.tag = page
            configureInteraction(for: spread)
            return spread
        }
        let view = dataSource?.pageContentView(readerView: self, pageNum: page) ?? UIView()
        view.tag = page
        configureInteraction(for: view)
        return view
    }

    func configureInteraction(for view: UIView) {
        guard let page = view as? RDPDFReaderPageInteractable else { return }
        // 所有阅读模式统一由 ReaderView 决定何时进入独立放大层；页面本身不再
        // 各自接管 pinch/double-tap，避免横屏左右页出现两套缩放坐标。
        page.readerSetInternalGesturesEnabled(false)
        page.readerContentTapHandler = { [weak self, weak view] point in
            guard let self, let view else { return }
            self.handleContentTap(view.convert(point, to: self))
        }
        page.readerZoomStateChangedHandler = { [weak self, weak view] zoomed in
            guard let self, view?.tag == self.currentPage else { return }
            self.isCurrentPageZoomed = zoomed
            self.updatePagingState()
        }
        page.readerSelectionStateChangedHandler = { [weak self, weak view] active in
            guard let self, view?.tag == self.currentPage else { return }
            self.isCurrentPageTextSelectionActive = active
            self.updatePagingState()
        }
    }

    func synchronizePageState() {
        isCurrentPageZoomed = (pageContentView(pageNum: currentPage) as? RDPDFReaderPageInteractable)?.readerIsZoomed ?? false
        isCurrentPageTextSelectionActive = (pageContentView(pageNum: currentPage) as? RDPDFReaderPageInteractable)?.readerHasActiveTextSelection ?? false
        updatePagingState()
    }

    func updatePagingState() {
        let enabled = isPagingEnabled && !isCurrentPageZoomed && !isCurrentPageTextSelectionActive
        collectionView.isScrollEnabled = enabled
        collectionView.panGestureRecognizer.isEnabled = enabled
        // 仿真翻页由 UIPageViewController 自己的手势驱动，不能只关闭外层
        // collectionView。画笔模式调用 `setPagingEnabled(false)` 后一并禁用它，
        // 这样单指始终交给内容页里的 DrawingCanvas，不会卷页。
        nativeCurlPageController?.gestureRecognizers.forEach { $0.isEnabled = enabled }
        curlPanGestureRecognizer.isEnabled = nativeCurlPageController == nil && currentDisplayType == .pageCurl
            && isPagingEnabled
            && !isCurrentPageTextSelectionActive
    }

    func transitionCurl(to page: Int, animated: Bool) {
        guard let controller = nativeCurlPageController else { return }
        let left = RDPDFReaderPageChildViewController(contentView: makeIndividualPageView(for: page), page: page)
        var children = [left]
        if usesLandscapeSpread {
            let rightPage = page + 1
            let rightContent = rightPage < pageCount() ? makeIndividualPageView(for: rightPage) : UIView()
            children.append(RDPDFReaderPageChildViewController(contentView: rightContent, page: rightPage))
        }
        let direction: UIPageViewController.NavigationDirection = page >= currentPage ? .forward : .reverse
        controller.setViewControllers(children, direction: direction, animated: animated) { [weak self] _ in
            self?.updateNativeCurlBookFrame()
        }
        currentPage = page
        if !animated {
            updateNativeCurlBookFrame()
        }
    }

    func makeIndividualPageView(for page: Int) -> UIView {
        let view = dataSource?.pageContentView(readerView: self, pageNum: page) ?? UIView()
        view.tag = page
        configureSpreadAlignment(for: view, page: page)
        configureInteraction(for: view)
        return view
    }

    func configureSpreadAlignment(for view: UIView, page: Int) {
        if let pdfPage = view as? RDPDFReaderPageView {
            if usesLandscapeSpread {
                // 原生双页卷页以偶数页为左页、奇数页为右页。
                // 左页内容贴右边，右页内容贴左边，两张 PDF 的纸张边缘直接相接。
                pdfPage.setSpreadContentAlignment(page.isMultiple(of: 2) ? .trailing : .leading)
            } else {
                pdfPage.setSpreadContentAlignment(.centered)
            }
        }
    }

    @objc func handleCurlPan(_ gesture: UIPanGestureRecognizer) {
        guard let page = curlContentView as? RDPDFReaderPageInteractable else { return }
        switch gesture.state {
        case .began:
            guard !page.readerHasActiveTextSelection else {
                curlPanInteraction = .idle
                return
            }
            if page.readerIsZoomed {
                curlPanInteraction = .contentPan
                page.readerBeginExternalPan()
            } else {
                curlPanInteraction = .pageTurn(startPage: currentPage)
            }
        case .changed:
            guard !page.readerHasActiveTextSelection else {
                curlPanInteraction = .idle
                return
            }
            if case .contentPan = curlPanInteraction {
                page.readerUpdateExternalPan(translation: gesture.translation(in: curlHostView))
            }
        case .ended:
            guard !page.readerHasActiveTextSelection else {
                curlPanInteraction = .idle
                return
            }
            finishCurlPan(gesture, page: page, cancelled: false)
        case .cancelled, .failed:
            finishCurlPan(gesture, page: page, cancelled: true)
        default:
            break
        }
    }

    private func finishCurlPan(
        _ gesture: UIPanGestureRecognizer,
        page: RDPDFReaderPageInteractable,
        cancelled: Bool
    ) {
        let interaction = curlPanInteraction
        curlPanInteraction = .idle
        switch interaction {
        case .contentPan:
            page.readerEndExternalPan()
        case let .pageTurn(startPage):
            guard !cancelled, currentPage == startPage else { return }
            let translation = gesture.translation(in: curlHostView)
            let velocity = gesture.velocity(in: curlHostView)
            guard abs(translation.x) > abs(translation.y) else { return }
            let crossedDistance = abs(translation.x) >= max(44, curlHostView.bounds.width * 0.12)
            let crossedVelocity = abs(velocity.x) >= 450
            guard crossedDistance || crossedVelocity else { return }
            let direction = abs(translation.x) >= 4 ? translation.x : velocity.x
            let step = usesLandscapeSpread ? 2 : 1
            transitionToPage(pageNum: startPage + (direction < 0 ? step : -step), animated: true)
        case .idle:
            break
        case .pinching:
            // 捏合拥有当前触摸序列，pan 的结束事件不能改变它的状态。
            curlPanInteraction = .pinching
        }
    }

    @objc func handleCurlPinch(_ gesture: UIPinchGestureRecognizer) {
        guard currentDisplayType == .pageCurl,
              let contentView = curlContentView,
              let page = contentView as? RDPDFReaderPageInteractable else { return }
        let point = gesture.location(in: contentView)
        switch gesture.state {
        case .began:
            if case .contentPan = curlPanInteraction {
                page.readerEndExternalPan()
            }
            // 第二根手指到来后，捏合优先，已产生的单指翻页候选立即失效。
            curlPanInteraction = .pinching
            page.readerBeginExternalPinch(at: point)
        case .changed:
            if case .pinching = curlPanInteraction {
                page.readerUpdateExternalPinch(scale: gesture.scale, at: point)
            }
        case .ended, .cancelled, .failed:
            page.readerEndExternalPinch()
            // 重置 recognizer，确保捏合结束后仍留在屏幕上的单根手指不会在
            // 同一触摸序列中重新变成翻页或内容拖动。
            curlPanGestureRecognizer.isEnabled = false
            curlPanInteraction = .idle
            curlPanGestureRecognizer.isEnabled = currentDisplayType == .pageCurl && isPagingEnabled
        default:
            break
        }
    }

    func handleContentTap(_ point: CGPoint) {
        if isCurrentPageTextSelectionActive {
            (curlContentView as? RDPDFReaderPageInteractable)?.readerClearTextSelection()
            return
        }
        // EPUB 的仿真模式由 UIPageViewController 接管翻页；内容点击只负责显隐工具栏。
        // PDF 的自定义仿真容器保持相同语义，避免边缘点击绕开横向翻页手势。
        guard currentDisplayType != .pageCurl else {
            toggleToolbars()
            return
        }
        // 手机横屏单页是连续竖滑阅读，翻页由滚动完成；点击不跳页，只显隐工具栏。
        guard !usesWidthFitVerticalScroll else {
            toggleToolbars()
            return
        }
        if isToolViewVisible {
            toggleToolbars()
        } else if point.x < bounds.width / 3 {
            transitionToPage(pageNum: currentPage - (usesLandscapeSpread ? 2 : 1), animated: true)
        } else if point.x > bounds.width * 2 / 3 {
            transitionToPage(pageNum: currentPage + (usesLandscapeSpread ? 2 : 1), animated: true)
        } else {
            toggleToolbars()
        }
    }
}

extension RDPDFReaderView: UIPageViewControllerDataSource, UIPageViewControllerDelegate {
    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let child = viewController as? RDPDFReaderPageChildViewController else { return nil }
        let page = child.page - 1
        guard page >= 0 else { return nil }
        return RDPDFReaderPageChildViewController(contentView: makeIndividualPageView(for: page), page: page)
    }

    public func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let child = viewController as? RDPDFReaderPageChildViewController else { return nil }
        let page = child.page + 1
        guard page < pageCount() else { return nil }
        return RDPDFReaderPageChildViewController(contentView: makeIndividualPageView(for: page), page: page)
    }

    public func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        guard completed, let child = pageViewController.viewControllers?.first as? RDPDFReaderPageChildViewController else { return }
        currentPage = child.page
        updateNativeCurlBookFrame()
    }
}