127 lines
4.6 KiB
Swift
127 lines
4.6 KiB
Swift
import Foundation
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/// BookPageMap 中的单个条目，记录一个章节的轻量元数据。
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/// 不持有 NSAttributedString，每条约 100 字节。
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struct RDEPUBBookPageMapEntry {
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let spineIndex: Int
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let href: String
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let title: String
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/// 该章节的页数
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let pageCount: Int
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/// 该章节在全书中的绝对起始页码（从 0 开始）
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let absolutePageStart: Int
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/// fragment ID → 字符偏移量映射
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let fragmentOffsets: [String: Int]
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}
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/// 全书轻量页码映射：仅存储每章的页数和起始位置，
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/// 内存成本约 100 字节/章，1000 章 ≈ 100KB。
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///
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/// 提供 spineIndex ↔ 绝对页码的双向查询，
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/// 用于进度条、目录跳转、位置恢复等不依赖内容的场景。
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struct RDEPUBBookPageMap {
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let entries: [RDEPUBBookPageMapEntry]
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/// 按 spineIndex 索引的查找表
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private let indexBySpine: [Int: Int] // spineIndex -> entries 数组下标
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/// 全书总页数
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let totalPages: Int
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init(entries: [RDEPUBBookPageMapEntry]) {
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self.entries = entries
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var mapping: [Int: Int] = [:]
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for (i, entry) in entries.enumerated() {
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mapping[entry.spineIndex] = i
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}
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self.indexBySpine = mapping
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self.totalPages = entries.last.map { $0.absolutePageStart + $0.pageCount } ?? 0
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}
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static let empty = RDEPUBBookPageMap(entries: [])
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// MARK: - 查询
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/// spineIndex + 本地页码 → 全书绝对页码
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func absolutePageIndex(spineIndex: Int, localPageIndex: Int) -> Int? {
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guard let idx = indexBySpine[spineIndex] else { return nil }
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let entry = entries[idx]
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guard localPageIndex >= 0, localPageIndex < entry.pageCount else { return nil }
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return entry.absolutePageStart + localPageIndex
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}
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/// 全书绝对页码 → spineIndex
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func spineIndex(forAbsolutePage absolutePage: Int) -> Int? {
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guard absolutePage >= 0, absolutePage < totalPages else { return nil }
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// 二分查找：entries 按 absolutePageStart 有序
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var lo = 0, hi = entries.count
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while lo < hi {
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let mid = lo + (hi - lo) / 2
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if entries[mid].absolutePageStart <= absolutePage {
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lo = mid + 1
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} else {
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hi = mid
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}
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}
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guard lo > 0 else { return nil }
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return entries[lo - 1].spineIndex
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}
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/// 全书绝对页码 → 本地页码（章节内偏移）
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func localPageIndex(forAbsolutePage absolutePage: Int) -> Int? {
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guard let si = spineIndex(forAbsolutePage: absolutePage),
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let idx = indexBySpine[si] else { return nil }
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let entry = entries[idx]
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let local = absolutePage - entry.absolutePageStart
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guard local >= 0, local < entry.pageCount else { return nil }
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return local
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}
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/// 获取指定 spineIndex 的条目
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func entry(forSpineIndex spineIndex: Int) -> RDEPUBBookPageMapEntry? {
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guard let idx = indexBySpine[spineIndex] else { return nil }
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return entries[idx]
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}
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/// 获取指定 spineIndex 在 entries 中的章节序号。
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func chapterIndex(forSpineIndex spineIndex: Int) -> Int? {
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indexBySpine[spineIndex]
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}
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/// 获取指定 spineIndex 的页数
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func pageCount(forSpineIndex spineIndex: Int) -> Int? {
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entry(forSpineIndex: spineIndex)?.pageCount
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}
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/// 全书总章节数
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var totalChapters: Int { entries.count }
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// MARK: - 构建
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/// Builder：从各章的 pageCount 逐步构建 BookPageMap
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struct Builder {
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private var items: [(spineIndex: Int, href: String, title: String, pageCount: Int, fragmentOffsets: [String: Int])] = []
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mutating func add(spineIndex: Int, href: String, title: String, pageCount: Int, fragmentOffsets: [String: Int]) {
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items.append((spineIndex, href, title, pageCount, fragmentOffsets))
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}
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func build() -> RDEPUBBookPageMap {
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// 按 spineIndex 排序
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let sorted = items.sorted { $0.spineIndex < $1.spineIndex }
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var entries: [RDEPUBBookPageMapEntry] = []
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var absolutePageStart = 0
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for item in sorted {
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entries.append(RDEPUBBookPageMapEntry(
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spineIndex: item.spineIndex,
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href: item.href,
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title: item.title,
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pageCount: item.pageCount,
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absolutePageStart: absolutePageStart,
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fragmentOffsets: item.fragmentOffsets
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))
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absolutePageStart += item.pageCount
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}
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return RDEPUBBookPageMap(entries: entries)
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}
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}
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}
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