391 lines
15 KiB
Swift
391 lines
15 KiB
Swift
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import UIKit
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protocol RDEpubReaderCachePolicyProviding {
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var shouldAvoidReaderPageCaching: Bool { get }
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}
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/// 页面视图被缓存彻底丢弃（旋转失效、窗口裁剪）时的即时清理钩子，
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/// 让持有重资源的页面（如活 WKWebView）不必等 dealloc 就能拆除内容。
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/// 实现方在之后再次被 configure 时必须能恢复可用。
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protocol RDEpubReaderPageResourceReleasing {
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func releaseResources()
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}
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/// 页面进入或离开当前阅读视口时的生命周期通知。
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/// 持有音视频等持续运行资源的页面应在离开时暂停，在重新进入时恢复。
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protocol RDEpubReaderPageVisibilityHandling: AnyObject {
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func readerPageVisibilityDidChange(isVisible: Bool)
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}
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final class RDEpubReaderPreloadController {
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var radius: Int = 2
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private let preloadHostView = UIView()
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private var preloadedPageViews: [Int: UIView] = [:]
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private var pageCurlCachedViews: [Int: UIView] = [:]
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private var cacheSignature: CacheSignature?
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struct Environment {
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let displayType: RDEpubReaderView.DisplayType
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let isLandscape: Bool
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let pagesPerScreen: Int
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let boundsSize: CGSize
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let landscapeDualPageEnabled: Bool
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let coverPageIndex: Int?
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let totalPages: Int
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let spreadResolver: RDEpubReaderSpreadResolver
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}
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private struct CacheSignature: Equatable {
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let displayType: RDEpubReaderView.DisplayType
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let isLandscape: Bool
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let pagesPerScreen: Int
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let boundsSize: CGSize
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}
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func setHostFrame(_ frame: CGRect) {
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preloadHostView.frame = frame
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}
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func ensureHostView(in parentView: UIView) {
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guard preloadHostView.superview == nil else { return }
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preloadHostView.isHidden = true
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preloadHostView.isUserInteractionEnabled = false
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preloadHostView.clipsToBounds = true
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preloadHostView.frame = parentView.bounds
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preloadHostView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
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parentView.insertSubview(preloadHostView, at: 0)
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}
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func initializeSignature(_ environment: Environment) {
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cacheSignature = currentCacheSignature(environment)
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}
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func invalidate(environment: Environment) {
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RDEpubReaderTapDebug.log(
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"PreloadController.invalidate",
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"clearing pageCurlCached=\(pageCurlCachedViews.keys.sorted()) preloaded=\(preloadedPageViews.keys.sorted())"
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)
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pageCurlCachedViews.values.forEach { discard($0) }
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preloadedPageViews.values.forEach { discard($0) }
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pageCurlCachedViews.removeAll()
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preloadedPageViews.removeAll()
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cacheSignature = currentCacheSignature(environment)
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}
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func pageViewForDisplay(
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pageNum: Int,
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environment: Environment,
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contentViewProvider: (Int, UIView?) -> UIView?
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) -> UIView {
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let view: UIView
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if let reusableView = detachedReusablePageView(for: pageNum) {
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view = reusableView
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RDEpubReaderTapDebug.log(
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"PreloadController.pageViewForDisplay",
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"cache HIT page=\(pageNum) view=\(RDEpubReaderTapDebug.describe(reusableView))"
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)
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} else {
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view = contentViewProvider(pageNum, nil) ?? UIView()
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RDEpubReaderTapDebug.log(
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"PreloadController.pageViewForDisplay",
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"cache MISS page=\(pageNum) created=\(RDEpubReaderTapDebug.describe(view))"
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)
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}
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if shouldCache(view: view, for: pageNum, environment: environment) {
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pageCurlCachedViews[pageNum] = view
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} else {
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pageCurlCachedViews.removeValue(forKey: pageNum)
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}
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return view
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}
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func takePreloadedView(for pageNum: Int) -> UIView? {
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let preloaded = preloadedPageViews.removeValue(forKey: pageNum)
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preloaded?.removeFromSuperview()
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RDEpubReaderTapDebug.log(
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"PreloadController.takePreloadedView",
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"cache \(preloaded == nil ? "MISS" : "HIT") page=\(pageNum) view=\(RDEpubReaderTapDebug.describe(preloaded))"
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)
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return preloaded
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}
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func updatePageVisibility(visiblePageNumbers: Set<Int>) {
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var notifiedViews = Set<ObjectIdentifier>()
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let cachedViews = pageCurlCachedViews.merging(preloadedPageViews) { current, _ in current }
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for (pageNumber, view) in cachedViews {
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let identifier = ObjectIdentifier(view)
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guard notifiedViews.insert(identifier).inserted else { continue }
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(view as? RDEpubReaderPageVisibilityHandling)?
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.readerPageVisibilityDidChange(isVisible: visiblePageNumbers.contains(pageNumber))
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}
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}
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func prime(
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around pageNum: Int,
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preferredForward: Bool? = nil,
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parentView: UIView,
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environment: Environment,
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contentViewProvider: (Int, UIView?) -> UIView?
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) {
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refreshCacheSignatureIfNeeded(environment)
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let targets = forecastTargets(around: pageNum, preferredForward: preferredForward, environment: environment)
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let keepSet = Set(targets).union(visiblePageNumbers(for: pageNum, environment: environment))
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trimCachedPageViews(keeping: keepSet)
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guard !targets.isEmpty else { return }
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ensureHostView(in: parentView)
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preloadHostView.frame = parentView.bounds
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for targetPage in targets {
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if let liveCached = pageCurlCachedViews[targetPage],
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liveCached.superview != nil,
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liveCached.superview !== preloadHostView {
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// 该页视图仍挂在翻页控制器的相邻页缓存上，内容已就绪。
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// 以前这里会误删缓存条目并创建一个从零加载的副本顶替，
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// 重内容页翻过去时拿到的是仍在加载的副本，表现为翻页后闪烁重置。
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RDEpubReaderTapDebug.log(
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"PreloadController.prime",
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"skip live page=\(targetPage) view=\(RDEpubReaderTapDebug.describe(liveCached))"
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)
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continue
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}
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let contentView: UIView
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if let existing = preloadedPageViews[targetPage], existing.superview === preloadHostView {
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contentView = existing
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RDEpubReaderTapDebug.log(
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"PreloadController.prime",
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"cache HIT(preloaded) page=\(targetPage) view=\(RDEpubReaderTapDebug.describe(existing))"
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)
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} else if let cached = pageCurlCachedViews.removeValue(forKey: targetPage), cached.superview == nil {
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contentView = cached
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RDEpubReaderTapDebug.log(
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"PreloadController.prime",
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"cache HIT(pageCurl) page=\(targetPage) view=\(RDEpubReaderTapDebug.describe(cached))"
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)
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} else {
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guard let providedView = contentViewProvider(targetPage, nil) else {
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// 页面提供者明确禁止预加载时不能塞入空白占位缓存，
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// 否则真实展示会直接命中白页而不再请求实际内容。
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preloadedPageViews.removeValue(forKey: targetPage)
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pageCurlCachedViews.removeValue(forKey: targetPage)
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continue
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}
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contentView = providedView
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RDEpubReaderTapDebug.log(
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"PreloadController.prime",
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"cache MISS page=\(targetPage) created=\(RDEpubReaderTapDebug.describe(contentView))"
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)
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}
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let shouldCacheContentView = shouldCache(view: contentView, for: targetPage, environment: environment)
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if shouldCacheContentView {
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preloadedPageViews[targetPage] = contentView
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} else {
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preloadedPageViews.removeValue(forKey: targetPage)
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}
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if contentView.superview !== preloadHostView {
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contentView.removeFromSuperview()
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preloadHostView.addSubview(contentView)
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}
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contentView.frame = preloadHostView.bounds
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if !shouldCacheContentView {
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contentView.removeFromSuperview()
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}
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}
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}
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private func currentCacheSignature(_ environment: Environment) -> CacheSignature {
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CacheSignature(
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displayType: environment.displayType,
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isLandscape: environment.isLandscape,
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pagesPerScreen: environment.pagesPerScreen,
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boundsSize: environment.boundsSize
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)
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}
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private func refreshCacheSignatureIfNeeded(_ environment: Environment) {
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let signature = currentCacheSignature(environment)
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if cacheSignature != signature {
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invalidate(environment: environment)
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} else if cacheSignature == nil {
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cacheSignature = signature
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}
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}
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private func shouldCachePage(_ pageNum: Int, environment: Environment) -> Bool {
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pageNum >= 0
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&& pageNum != RDEpubReaderView.blankPageNum
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&& pageNum != RDEpubReaderView.blankEndPageNum
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&& pageNum < environment.totalPages
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}
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private func shouldCache(view: UIView, for pageNum: Int, environment: Environment) -> Bool {
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guard shouldCachePage(pageNum, environment: environment) else { return false }
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if let policyProvider = view as? RDEpubReaderCachePolicyProviding {
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return !policyProvider.shouldAvoidReaderPageCaching
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}
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return true
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}
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private func isDualPage(environment: Environment) -> Bool {
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environment.landscapeDualPageEnabled
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&& environment.isLandscape
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&& environment.displayType != .verticalScroll
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}
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private func spreadStart(for pageNum: Int, environment: Environment) -> Int? {
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guard shouldCachePage(pageNum, environment: environment) else { return nil }
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guard isDualPage(environment: environment) else { return pageNum }
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return environment.spreadResolver.dualPagePair(
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for: pageNum,
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totalPages: environment.totalPages,
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coverPageIndex: environment.coverPageIndex
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).left
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}
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private func spreadPageNumbers(startingAt pageNum: Int, environment: Environment) -> Set<Int> {
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guard shouldCachePage(pageNum, environment: environment) else { return [] }
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guard isDualPage(environment: environment) else { return [pageNum] }
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let pair = environment.spreadResolver.dualPagePair(
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for: pageNum,
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totalPages: environment.totalPages,
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coverPageIndex: environment.coverPageIndex
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)
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var pages: Set<Int> = [pair.left]
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if let right = pair.right, shouldCachePage(right, environment: environment) {
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pages.insert(right)
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}
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return pages
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}
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private func adjacentSpreadStart(from pageNum: Int, forward: Bool, environment: Environment) -> Int? {
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guard environment.totalPages > 0,
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let spreadStart = spreadStart(for: pageNum, environment: environment) else {
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return nil
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}
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guard isDualPage(environment: environment) else {
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let target = forward ? spreadStart + 1 : spreadStart - 1
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return shouldCachePage(target, environment: environment) ? target : nil
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}
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if forward {
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return environment.spreadResolver.adjacentDualPage(
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from: spreadStart,
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totalPages: environment.totalPages,
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coverPageIndex: environment.coverPageIndex,
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forward: true
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)
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}
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let pair = environment.spreadResolver.dualPagePair(
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for: spreadStart,
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totalPages: environment.totalPages,
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coverPageIndex: environment.coverPageIndex
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)
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let prevEnd = pair.left - 1
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guard prevEnd >= 0 else { return nil }
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return environment.spreadResolver.dualPagePair(
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for: prevEnd,
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totalPages: environment.totalPages,
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coverPageIndex: environment.coverPageIndex
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).left
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}
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private func visiblePageNumbers(for anchorPage: Int, environment: Environment) -> Set<Int> {
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spreadPageNumbers(startingAt: anchorPage, environment: environment)
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}
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private func detachedReusablePageView(for pageNum: Int) -> UIView? {
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if let preloaded = preloadedPageViews.removeValue(forKey: pageNum) {
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preloaded.removeFromSuperview()
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return preloaded
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}
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guard let cached = pageCurlCachedViews[pageNum], cached.superview == nil else {
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return nil
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}
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pageCurlCachedViews.removeValue(forKey: pageNum)
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return cached
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}
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private func trimCachedPageViews(keeping pageNumbers: Set<Int>) {
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pageCurlCachedViews = pageCurlCachedViews.filter { key, value in
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let keep = pageNumbers.contains(key)
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if !keep {
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discard(value)
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}
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return keep
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}
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preloadedPageViews = preloadedPageViews.filter { key, value in
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let keep = pageNumbers.contains(key)
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if !keep {
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discard(value)
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}
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return keep
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}
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}
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private func discard(_ view: UIView) {
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// 只有闲置视图（未挂载或还在预加载宿主里）才能立即拆除内容；
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// 挂在子 VC / cell 上的视图可能正在展示或会被 UIPageViewController
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// 的缓存重新呈现，提前拆除会让翻页露出空白页。这类视图交由持有方
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// 释放后经 deinit 自然回收（弱代理已保证无保留环）。
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let isHeldOutsidePreloadHost = view.superview != nil && view.superview !== preloadHostView
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view.removeFromSuperview()
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if !isHeldOutsidePreloadHost {
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(view as? RDEpubReaderPageResourceReleasing)?.releaseResources()
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}
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}
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private func forecastTargets(around pageNum: Int, preferredForward: Bool?, environment: Environment) -> [Int] {
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guard environment.totalPages > 0,
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shouldCachePage(pageNum, environment: environment) else {
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return []
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}
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var targets = Set<Int>()
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var previousAnchor = pageNum
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for _ in 0..<max(radius, 0) {
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guard let previous = adjacentSpreadStart(from: previousAnchor, forward: false, environment: environment) else { break }
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targets.formUnion(spreadPageNumbers(startingAt: previous, environment: environment))
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previousAnchor = previous
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}
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var nextAnchor = pageNum
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for _ in 0..<max(radius, 0) {
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guard let next = adjacentSpreadStart(from: nextAnchor, forward: true, environment: environment) else { break }
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targets.formUnion(spreadPageNumbers(startingAt: next, environment: environment))
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nextAnchor = next
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}
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if let preferredForward,
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let edgeAnchor = preferredForward ? adjacentSpreadStart(from: nextAnchor, forward: true, environment: environment)
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: adjacentSpreadStart(from: previousAnchor, forward: false, environment: environment) {
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targets.formUnion(spreadPageNumbers(startingAt: edgeAnchor, environment: environment))
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}
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return targets.sorted()
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}
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}
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