import UIKit

/// EPUB 文本书籍构建器，负责将 EPUB publication 渲染、分页并组装为 `RDEPUBTextBook`。
public final class RDEPUBTextBookBuilder {
    private let renderer: RDEPUBTextRenderer
    private let cache: RDEPUBTextBookCache?
    private let layoutConfig: RDEPUBTextLayoutConfig
    private let sampler: RDEPUBTextPerformanceSampler
    private let renderPipeline: RDEPUBChapterRenderPipeline
    private let paginationPipeline: RDEPUBChapterPaginationPipeline
    private let tailNormalizer: RDEPUBChapterTailNormalizer
    private let cacheCoordinator: RDEPUBPaginationCacheCoordinator
    private let diagnosticsReporter: RDEPUBBuildDiagnosticsReporter

    /// 最后一次构建的资源引用诊断（样式表、图片等）
    public private(set) var lastBuildResourceDiagnostics: [RDEPUBTextResourceReferenceDiagnostic] = []
    /// 最后一次构建的分页诊断（每章一页的分页原因、附件统计等）
    public private(set) var lastBuildPaginationDiagnostics: [RDEPUBTextChapterPaginationDiagnostic] = []
    /// 最后一次构建的性能采样数据
    public private(set) var lastBuildPerformanceSamples: [RDEPUBTextPerformanceSample] = []
    /// 最后一次构建的缓存命中/未命中统计
    public private(set) var lastBuildCacheStats: (hits: Int, misses: Int) = (0, 0)

    /// 创建书籍构建器。
    /// - Parameters:
    ///   - renderer: 文本渲染器
    ///   - cache: 分页缓存（可选）
    ///   - layoutConfig: 页面布局配置
    public init(
        renderer: RDEPUBTextRenderer,
        cache: RDEPUBTextBookCache? = nil,
        layoutConfig: RDEPUBTextLayoutConfig = .default
    ) {
        self.renderer = renderer
        self.cache = cache
        self.layoutConfig = layoutConfig
        self.sampler = RDEPUBTextPerformanceSampler()
        self.renderPipeline = RDEPUBChapterRenderPipeline(renderer: renderer)
        self.paginationPipeline = RDEPUBChapterPaginationPipeline()
        self.tailNormalizer = RDEPUBChapterTailNormalizer()
        self.cacheCoordinator = RDEPUBPaginationCacheCoordinator(cache: cache, layoutConfig: layoutConfig)
        self.diagnosticsReporter = RDEPUBBuildDiagnosticsReporter()
    }

    /// 默认构造器，使用 DTCoreText 渲染器
    public convenience init() {
        self.init(renderer: RDEPUBDTCoreTextRenderer())
    }

    private var isPaginationDebugEnabled: Bool {
        ProcessInfo.processInfo.arguments.contains("--demo-pagination-debug")
    }

    /// 生成最近一次构建的语义摘要，用于 Phase 7 质量检测日志
    public func phase7SemanticSummary(title: String? = nil) -> String? {
        diagnosticsReporter.phase7SemanticSummary(
            title: title,
            diagnostics: lastBuildPaginationDiagnostics
        )
    }

    /// 核心构建方法：从 EPUB publication 构建分页书籍。
    ///
    /// 流程：
    /// 1. 生成缓存键，尝试加载分页缓存
    /// 2. 遍历 spine 中的线性 HTML 章节
    /// 3. 渲染每章 HTML → NSAttributedString
    /// 4. 跳过空白的封面/扉页章节
    /// 5. 分页：缓存命中则使用缓存的页范围，否则调用 CoreText 分页引擎
    /// 6. 尾页规范化：丢弃纯空白尾页、合并过短尾页
    /// 7. 构建 RDEPUBTextBook 并保存分页缓存
    public func build(
        parser: RDEPUBParser,
        publication: RDEPUBPublication,
        pageSize: CGSize,
        style: RDEPUBTextRenderStyle
    ) throws -> RDEPUBTextBook {
        if isPaginationDebugEnabled {
            print("[PaginationDebug] build pageSize=\(NSCoder.string(for: pageSize)) layoutInsets=\(NSCoder.string(for: layoutConfig.edgeInsets))")
        }
        var chapters: [RDEPUBTextChapter] = []
        var flatPages: [RDEPUBTextPage] = []
        lastBuildResourceDiagnostics = []
        lastBuildPaginationDiagnostics = []
        lastBuildPerformanceSamples = []
        lastBuildCacheStats = (0, 0)
        sampler.reset()

        let buildStart = CFAbsoluteTimeGetCurrent()

        // 缓存查询 — WXRead 模式：只加载每章的页范围，不缓存富文本
        let bookID = publication.metadata.identifier ?? publication.metadata.title
        let cacheKey = cacheCoordinator.cacheKey(bookID: bookID, pageSize: pageSize, style: style)
        let cachedPagination = cacheCoordinator.load(key: cacheKey)

        for (spineIndex, item) in publication.spine.enumerated() where item.linear {
            guard let result = try buildChapter(
                parser: parser,
                publication: publication,
                spineIndex: spineIndex,
                pageSize: pageSize,
                style: style,
                chapterIndex: chapters.count,
                absolutePageStartIndex: flatPages.count,
                cachedPagination: cachedPagination
            ) else { continue }

            if isPaginationDebugEnabled,
               item.href.contains("Chapter_3.xhtml") {
                let pages = result.chapter.pages
                print("[PaginationDebug] href=\(item.href) pages=\(pages.count)")
                for page in pages {
                    let preview = debugPreview(for: page.content, limit: 36)
                    print("[PaginationDebug] absPage=\(page.absolutePageIndex + 1) localPage=\(page.pageIndexInChapter + 1) range=\(NSStringFromRange(page.contentRange)) break=\(page.metadata.breakReason.rawValue) preview=\(preview)")
                    for note in page.metadata.diagnostics.prefix(4) {
                        print("[PaginationDebug] note=\(note)")
                    }
                }
            }

            chapters.append(result.chapter)
            flatPages.append(contentsOf: result.chapter.pages)
            lastBuildResourceDiagnostics.append(contentsOf: result.resourceDiagnostics)
            lastBuildPaginationDiagnostics.append(result.paginationDiagnostic)
            sampler.record(result.performanceSample)
            if result.cacheHit {
                lastBuildCacheStats.hits += 1
            } else {
                lastBuildCacheStats.misses += 1
            }
        }

        let book = RDEPUBTextBook(chapters: chapters, pages: flatPages)

        sampler.totalBuildDuration = CFAbsoluteTimeGetCurrent() - buildStart

        // 保存分页缓存（只缓存页范围和分页原因，不缓存富文本）
        cacheCoordinator.save(chapters: chapters, key: cacheKey)

        #if DEBUG
        print(sampler.summary())
        #endif
        lastBuildPerformanceSamples = sampler.samples

        return book
    }

    /// 构建指定 spine 章节，用于大书快速首屏和后台增量补齐。
    public func buildChapter(
        parser: RDEPUBParser,
        publication: RDEPUBPublication,
        spineIndex: Int,
        pageSize: CGSize,
        style: RDEPUBTextRenderStyle,
        chapterIndex: Int = 0,
        absolutePageStartIndex: Int = 0
    ) throws -> RDEPUBTextChapterBuildResult? {
        let bookID = publication.metadata.identifier ?? publication.metadata.title
        let cacheKey = cacheCoordinator.cacheKey(bookID: bookID, pageSize: pageSize, style: style)
        let cachedPagination = cacheCoordinator.load(key: cacheKey)
        return try buildChapter(
            parser: parser,
            publication: publication,
            spineIndex: spineIndex,
            pageSize: pageSize,
            style: style,
            chapterIndex: chapterIndex,
            absolutePageStartIndex: absolutePageStartIndex,
            cachedPagination: cachedPagination
        )
    }

    private func buildChapter(
        parser: RDEPUBParser,
        publication: RDEPUBPublication,
        spineIndex: Int,
        pageSize: CGSize,
        style: RDEPUBTextRenderStyle,
        chapterIndex: Int,
        absolutePageStartIndex: Int,
        cachedPagination: [String: RDEPUBTextChapterPaginationCache]?
    ) throws -> RDEPUBTextChapterBuildResult? {
        guard publication.spine.indices.contains(spineIndex) else { return nil }
        let item = publication.spine[spineIndex]
        guard item.linear,
              item.mediaType.contains("html") || item.mediaType.contains("xhtml"),
              let rawHTML = parser.htmlString(forRelativePath: item.href) else {
            return nil
        }

        let chapterTitle = resolvedChapterTitle(for: item, toc: publication.tableOfContents)
        let request = RDEPUBTextTypesetterPipeline().makeRequest(
            from: RDEPUBTypesettingInput(
                href: item.href,
                title: chapterTitle,
                rawHTML: rawHTML,
                baseURL: parser.fileURL(forRelativePath: item.href)?.deletingLastPathComponent(),
                style: style,
                resourceResolver: publication.resourceResolver,
                contentLanguageCode: publication.metadata.language,
                pageSize: pageSize,
                layoutConfig: layoutConfig
            )
        ).request

        let renderStart = CFAbsoluteTimeGetCurrent()
        let rendered = try renderPipeline.render(request)
        let renderDuration = CFAbsoluteTimeGetCurrent() - renderStart

        let plainText = rendered.attributedString.string.trimmingCharacters(in: .whitespacesAndNewlines)
        if item.href.lowercased().contains("cover") {
            #if DEBUG
            print("[EPUB][Cover] rendered href=\(item.href) textLength=\(plainText.count) attrLength=\(rendered.attributedString.length) attachments=\(attachmentCount(in: rendered.attributedString))")
            #endif
        }
        if shouldSkipChapter(item: item, content: rendered.attributedString, text: plainText) {
            if item.href.lowercased().contains("cover") {
                #if DEBUG
                print("[EPUB][Cover] skipped href=\(item.href)")
                #endif
            }
            return nil
        }

        let content = NSMutableAttributedString(attributedString: rendered.attributedString)
        let paginateStart = CFAbsoluteTimeGetCurrent()
        let layoutFrames: [RDEPUBTextLayoutFrame]
        let isCacheHit: Bool

        if isAttachmentOnlyCoverChapter(item: item, content: content, plainText: plainText) {
            layoutFrames = [
                RDEPUBTextLayoutFrame(
                    contentRange: NSRange(location: 0, length: content.length),
                    breakReason: .chapterEnd,
                    blockRange: nil,
                    attachmentRanges: attachmentRanges(in: content),
                    attachmentKinds: [],
                    blockKinds: [],
                    semanticHints: [],
                    attachmentPlacements: [],
                    trailingFragmentID: nil,
                    diagnostics: [
                        "page break: chapterEnd",
                        "cover fallback: single attachment page",
                        "page range: \(NSStringFromRange(NSRange(location: 0, length: content.length)))"
                    ]
                )
            ]
            isCacheHit = false
        } else if let cached = cachedPagination?[item.href] {
            layoutFrames = cached.pageRanges.enumerated().map { idx, range in
                let breakReason = idx < cached.breakReasons.count ? cached.breakReasons[idx] : .frameLimit
                return RDEPUBTextLayoutFrame(
                    contentRange: range,
                    breakReason: breakReason,
                    blockRange: nil,
                    attachmentRanges: [],
                    attachmentKinds: [],
                    blockKinds: [],
                    semanticHints: cached.semanticHints,
                    attachmentPlacements: [],
                    trailingFragmentID: nil,
                    diagnostics: [
                        "page break: \(breakReason.rawValue)",
                        "page range: \(NSStringFromRange(range))",
                        "source: cache hit"
                    ]
                )
            }
            isCacheHit = true
        } else {
            layoutFrames = content.length > 0
                ? paginationPipeline.frames(
                    for: content,
                    pageSize: pageSize,
                    config: layoutConfig,
                    fragmentOffsets: rendered.fragmentOffsets
                )
                : []
            isCacheHit = false
        }

        let paginateDuration = CFAbsoluteTimeGetCurrent() - paginateStart
        let normalizedFrames = tailNormalizer.normalize(
            layoutFrames,
            content: content,
            href: item.href
        )
        let effectiveFrames = normalizedFrames.isEmpty && content.length > 0
            ? [
                RDEPUBTextLayoutFrame(
                    contentRange: NSRange(location: 0, length: content.length),
                    breakReason: .chapterEnd,
                    blockRange: nil,
                    attachmentRanges: [],
                    attachmentKinds: [],
                    blockKinds: [],
                    semanticHints: [],
                    attachmentPlacements: [],
                    trailingFragmentID: nil,
                    diagnostics: [
                        "page break: chapterEnd",
                        "page range: \(NSStringFromRange(NSRange(location: 0, length: content.length)))"
                    ]
                )
            ]
            : normalizedFrames

        if item.href.lowercased().contains("cover") {
            #if DEBUG
            print("[EPUB][Cover] paginated href=\(item.href) pages=\(effectiveFrames.count) firstRange=\(effectiveFrames.first.map { NSStringFromRange($0.contentRange) } ?? "none")")
            #endif
        }

        let chapterAttributedContent = content.copy() as! NSAttributedString
        let pages = effectiveFrames.enumerated().map { localPageIndex, frame in
            let range = frame.contentRange
            return RDEPUBTextPage(
                absolutePageIndex: absolutePageStartIndex + localPageIndex,
                chapterIndex: chapterIndex,
                spineIndex: spineIndex,
                href: item.href,
                chapterTitle: chapterTitle,
                pageIndexInChapter: localPageIndex,
                totalPagesInChapter: effectiveFrames.count,
                chapterContent: chapterAttributedContent,
                content: content.attributedSubstring(from: range),
                contentRange: range,
                pageStartOffset: range.location,
                pageEndOffset: range.location + max(range.length - 1, 0),
                metadata: frame.metadata
            )
        }

        let chapter = RDEPUBTextChapter(
            chapterIndex: chapterIndex,
            spineIndex: spineIndex,
            href: item.href,
            title: chapterTitle,
            attributedContent: chapterAttributedContent,
            fragmentOffsets: rendered.fragmentOffsets,
            pageBreakReasons: pages.map(\.metadata.breakReason),
            pages: pages
        )
        let performanceSample = RDEPUBTextPerformanceSample(
            chapterHref: item.href,
            renderDuration: renderDuration,
            paginateDuration: paginateDuration,
            pageCount: effectiveFrames.count,
            attributedStringLength: content.length,
            cacheHit: isCacheHit
        )
        let diagnostic = diagnosticsReporter.chapterDiagnostic(
            href: item.href,
            title: chapterTitle,
            pages: pages
        )

        return RDEPUBTextChapterBuildResult(
            chapter: chapter,
            resourceDiagnostics: rendered.resourceDiagnostics,
            paginationDiagnostic: diagnostic,
            performanceSample: performanceSample,
            cacheHit: isCacheHit
        )
    }

    // MARK: - 章节标题解析

    /// 从目录表中查找章节标题，找不到则回退到 spine item 的 title 或 href
    private func resolvedChapterTitle(for item: RDEPUBSpineItem, toc: [EPUBTableOfContentsItem]) -> String {
        if let title = flattenedTOCItems(from: toc).first(where: { tocItem in
            tocItem.href.components(separatedBy: "#").first == item.href
        })?.title.trimmingCharacters(in: .whitespacesAndNewlines), !title.isEmpty {
            return title
        }
        let trimmedTitle = item.title.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmedTitle.isEmpty ? item.href : trimmedTitle
    }

    /// 递归展开嵌套目录为扁平列表
    private func flattenedTOCItems(from items: [EPUBTableOfContentsItem]) -> [EPUBTableOfContentsItem] {
        items.flatMap { item in
            [item] + flattenedTOCItems(from: item.children)
        }
    }

    // MARK: - 章节过滤

    /// 判断是否应跳过该章节（空白的封面/扉页，无文本且无附件）
    private func shouldSkipChapter(item: RDEPUBSpineItem, content: NSAttributedString, text: String) -> Bool {
        let lowercasedHref = item.href.lowercased()
        var hasAttachment = false
        if content.length > 0 {
            content.enumerateAttribute(.attachment, in: NSRange(location: 0, length: content.length)) { value, _, stop in
                guard value != nil else { return }
                hasAttachment = true
                stop.pointee = true
            }
        }
        if text.isEmpty && !hasAttachment && (lowercasedHref.contains("cover") || lowercasedHref.contains("title")) {
            return true
        }
        return false
    }

    // MARK: - 附件统计

    /// 统计富文本中的附件数量
    private func attachmentCount(in content: NSAttributedString) -> Int {
        guard content.length > 0 else { return 0 }
        var count = 0
        content.enumerateAttribute(.attachment, in: NSRange(location: 0, length: content.length)) { value, _, _ in
            if value != nil {
                count += 1
            }
        }
        return count
    }

    /// 获取富文本中所有附件的 NSRange 列表
    private func attachmentRanges(in content: NSAttributedString) -> [NSRange] {
        guard content.length > 0 else { return [] }
        var ranges: [NSRange] = []
        content.enumerateAttribute(.attachment, in: NSRange(location: 0, length: content.length)) { value, range, _ in
            if value != nil {
                ranges.append(range)
            }
        }
        return ranges
    }

    // MARK: - 封面章节检测

    /// 判断是否为纯图片封面章节（href 包含 cover 且有附件但几乎无文本）
    private func isAttachmentOnlyCoverChapter(
        item: RDEPUBSpineItem,
        content: NSAttributedString,
        plainText: String
    ) -> Bool {
        let lowercasedHref = item.href.lowercased()
        guard lowercasedHref.contains("cover") else { return false }
        let trimmed = plainText.trimmingCharacters(in: .whitespacesAndNewlines)
        return attachmentCount(in: content) > 0 && trimmed.count <= 1
    }

    private func debugPreview(for content: NSAttributedString, limit: Int) -> String {
        let collapsed = content.string
            .replacingOccurrences(of: "\n", with: " ")
            .replacingOccurrences(of: "\r", with: " ")
            .replacingOccurrences(of: "\t", with: " ")
            .trimmingCharacters(in: .whitespacesAndNewlines)
        guard !collapsed.isEmpty else { return "<empty>" }
        if collapsed.count <= limit {
            return collapsed
        }
        let head = collapsed.prefix(limit)
        return "\(head)…"
    }

}