ReadViewSDK/Sources/RDPDFReaderView/Sources/RDPDFReaderKitView.swift

import UIKit

public protocol RDPDFReaderKitViewDataSource: AnyObject {
    func numberOfPages(in readerView: RDPDFReaderKitView) -> Int
    func readerView(_ readerView: RDPDFReaderKitView, imageForPageAt index: Int) -> UIImage?
}

public protocol RDPDFReaderKitViewDelegate: AnyObject {
    func readerView(_ readerView: RDPDFReaderKitView, didMoveToPage index: Int)
}

/// 独立 PDF 阅读容器：仅处理分页和页面缩放，不依赖主工程的下载/缓存/数据库。
public final class RDPDFReaderKitView: UIView, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    public weak var dataSource: RDPDFReaderKitViewDataSource?
    public weak var delegate: RDPDFReaderKitViewDelegate?
    public private(set) var currentPage = 0

    /// 业务层可把画笔叠加到 `RDPDFZoomablePageView.contentView`；此状态禁止单指翻页，
    /// 同时保留页面的双指缩放和双指拖动。
    public var isDrawingMode = false {
        didSet { updatePagingInteraction() }
    }

    public var onConfigurePage: ((RDPDFZoomablePageView, Int) -> Void)?

    private let layout: UICollectionViewFlowLayout = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        return layout
    }()
    private lazy var collectionView: UICollectionView = {
        let view = UICollectionView(frame: .zero, collectionViewLayout: layout)
        view.backgroundColor = UIColor(white: 0.93, alpha: 1)
        view.isPagingEnabled = true
        view.showsHorizontalScrollIndicator = false
        view.dataSource = self
        view.delegate = self
        view.panGestureRecognizer.maximumNumberOfTouches = 1
        view.register(PageCell.self, forCellWithReuseIdentifier: PageCell.reuseIdentifier)
        return view
    }()
    private var isCurrentPageZoomed = false

    public override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(collectionView)
    }

    public required init?(coder: NSCoder) {
        super.init(coder: coder)
        addSubview(collectionView)
    }

    public override func layoutSubviews() {
        super.layoutSubviews()
        collectionView.frame = bounds
        layout.itemSize = bounds.size
    }

    public func reloadData() {
        let pageCount = dataSource?.numberOfPages(in: self) ?? 0
        currentPage = max(0, min(currentPage, max(0, pageCount - 1)))
        isCurrentPageZoomed = false
        collectionView.reloadData()
        collectionView.layoutIfNeeded()
        collectionView.setContentOffset(CGPoint(x: CGFloat(currentPage) * bounds.width, y: 0), animated: false)
        updatePagingInteraction()
    }

    public func go(to page: Int, animated: Bool = true) {
        let count = dataSource?.numberOfPages(in: self) ?? 0
        guard count > 0 else { return }
        let target = max(0, min(page, count - 1))
        guard !isDrawingMode, !isCurrentPageZoomed else { return }
        currentPage = target
        collectionView.setContentOffset(CGPoint(x: CGFloat(target) * bounds.width, y: 0), animated: animated)
        delegate?.readerView(self, didMoveToPage: target)
    }

    public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        dataSource?.numberOfPages(in: self) ?? 0
    }

    public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PageCell.reuseIdentifier, for: indexPath) as! PageCell
        let pageView = cell.pageView
        pageView.image = dataSource?.readerView(self, imageForPageAt: indexPath.item)
        pageView.isDrawingMode = isDrawingMode
        pageView.zoomStateChanged = { [weak self, weak pageView] zoomed in
            guard let self, let pageView, pageView.tag == self.currentPage else { return }
            self.isCurrentPageZoomed = zoomed
            self.updatePagingInteraction()
        }
        pageView.tag = indexPath.item
        onConfigurePage?(pageView, indexPath.item)
        return cell
    }

    public func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        updateCurrentPageFromOffset()
    }

    public func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
        updateCurrentPageFromOffset()
    }

    private func updateCurrentPageFromOffset() {
        guard bounds.width > 0 else { return }
        let page = Int((collectionView.contentOffset.x / bounds.width).rounded())
        guard page != currentPage else { return }
        currentPage = page
        isCurrentPageZoomed = false
        updatePagingInteraction()
        delegate?.readerView(self, didMoveToPage: page)
    }

    private func updatePagingInteraction() {
        collectionView.isScrollEnabled = !isDrawingMode && !isCurrentPageZoomed
        collectionView.visibleCells
            .compactMap { ($0 as? PageCell)?.pageView }
            .forEach { $0.isDrawingMode = isDrawingMode }
    }
}

private final class PageCell: UICollectionViewCell {
    static let reuseIdentifier = "RDPDFReaderKitView.PageCell"
    let pageView = RDPDFZoomablePageView()

    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.addSubview(pageView)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func layoutSubviews() {
        super.layoutSubviews()
        pageView.frame = contentView.bounds
    }

    override func prepareForReuse() {
        super.prepareForReuse()
        pageView.resetZoom()
        pageView.zoomStateChanged = nil
    }
}