import Foundation

/// EPUB 阅读器分页协调器：负责出版物的分页计算和页面数据更新。
///
/// 职责：
/// - 根据出版物类型（文本重排/Fixed Layout/Web 内容）选择分页策略
/// - 后台构建文本图书模型并应用分页快照
/// - 重新分页时保持当前阅读位置
/// - 刷新可见内容并保持位置
/// - 重建外部纯文本图书
final class RDEPUBReaderPaginationCoordinator {
    private unowned let context: RDEPUBReaderContext

    init(context: RDEPUBReaderContext) {
        self.context = context
    }

    /// 对出版物执行分页：文本重排走 TextBookBuilder，Fixed Layout 直接生成快照，Web 内容走 Paginator。
    func paginatePublication(restoreLocation: RDEPUBLocation?) {
        guard let controller = context.controller,
              let parser = context.parser,
              let publication = context.publication,
              let readingSession = context.readingSession else {
            return
        }

        controller.isRepaginating = true
        controller.errorLabel.isHidden = true
        controller.showLoading()
        let token = UUID()
        context.paginationToken = token

        if publication.readingProfile == .textReflowable {
            let pageSize = controller.currentTextPageSize()
            context.lastTextPaginationPageSize = pageSize
            let layoutConfig = controller.currentTextLayoutConfig(pageSize: pageSize)
            let builder = context.makeTextBookBuilder(layoutConfig: layoutConfig)
            let renderStyle = controller.currentTextRenderStyle()

            DispatchQueue.global(qos: .userInitiated).async { [weak controller] in
                guard let controller else { return }
                do {
                    let textBook = try builder.build(
                        parser: parser,
                        publication: publication,
                        pageSize: pageSize,
                        style: renderStyle
                    )
                    DispatchQueue.main.async {
                        guard self.context.paginationToken == token else { return }
                        self.context.runtime?.applyTextBook(textBook, restoreLocation: restoreLocation)
                    }
                } catch {
                    DispatchQueue.main.async {
                        guard self.context.paginationToken == token else { return }
                        self.context.handle(error: error)
                    }
                }
            }
            return
        }

        if publication.layout == .fixed {
            let snapshot = readingSession.makePaginationSnapshot(
                pageCounts: Array(repeating: 1, count: publication.spine.count),
                preferences: controller.currentPreferences(),
                layoutContext: controller.currentLayoutContext()
            )
            context.runtime?.applyPaginationSnapshot(snapshot, restoreLocation: restoreLocation)
            return
        }

        let paginator = context.makePaginator()
        context.paginator = paginator
        paginator.calculate(
            parser: parser,
            hostingView: controller.ensurePaginationHostView(),
            presentation: controller.currentPreferences().presentationStyle(viewportSize: controller.currentLayoutContext().viewportSize)
        ) { [weak controller] pageCounts in
            guard let controller, self.context.paginationToken == token else { return }
            let snapshot = readingSession.makePaginationSnapshot(
                pageCounts: pageCounts,
                preferences: controller.currentPreferences(),
                layoutContext: controller.currentLayoutContext()
            )
            self.context.paginator = nil
            self.context.runtime?.applyPaginationSnapshot(snapshot, restoreLocation: restoreLocation)
        }
    }

    /// 应用文本图书模型：生成分页快照并完成分页流程。
    func applyTextBook(_ textBook: RDEPUBTextBook, restoreLocation: RDEPUBLocation?) {
        guard let controller = context.controller else { return }
        context.textBook = textBook
        let snapshot = controller.nativeTextSnapshot(from: textBook)
        context.replaceActiveSnapshot(snapshot)

        guard !textBook.pages.isEmpty else {
            context.handle(error: RDEPUBParserError.emptySpine)
            return
        }

        finishPagination(restoreLocation: restoreLocation)
    }

    /// 应用分页快照（Fixed Layout 或 Web 内容），并完成分页流程。
    func applyPaginationSnapshot(
        _ snapshot: (pages: [EPUBPage], chapters: [EPUBChapterInfo]),
        restoreLocation: RDEPUBLocation?
    ) {
        guard let controller = context.controller else { return }
        context.textBook = nil
        context.replaceActiveSnapshot(snapshot)

        guard !snapshot.pages.isEmpty else {
            context.handle(error: RDEPUBParserError.emptySpine)
            return
        }

        finishPagination(restoreLocation: restoreLocation)
    }

    /// 分页完成后的收尾：刷新视图、恢复阅读位置、处理待定视口变更。
    func finishPagination(restoreLocation: RDEPUBLocation?) {
        guard let controller = context.controller,
              let readerView = context.readerView else { return }
        controller.isRepaginating = false
        controller.hideLoading()
        readerView.reloadData()
        if let targetLocation = restoreLocation {
            controller.restoreReadingLocation(targetLocation)
        } else {
            readerView.transitionToPage(pageNum: 0)
            context.readingSession?.transition(to: .idle)
        }

        context.runtime?.viewportMonitor.processPendingChangeAfterPagination()
    }

    /// 重新分页并保持当前阅读位置（优先使用待恢复位置，其次当前位置，最后持久化位置）。
    func repaginatePreservingCurrentLocation() {
        guard context.publication != nil else { return }
        let restoreLocation = context.runtime?.viewportMonitor.consumePendingPresentationRestoreLocation()
            ?? context.currentVisibleLocation()
            ?? context.persistenceLocation()
        paginatePublication(restoreLocation: restoreLocation)
    }

    /// 刷新可见内容并保持当前阅读位置不变。
    func refreshVisibleContentPreservingLocation() {
        guard let readerView = context.readerView else { return }
        let restoreLocation = context.currentVisibleLocation() ?? context.persistenceLocation()
        readerView.reloadData()
        if let restoreLocation {
            _ = context.restoreReadingLocation(restoreLocation)
        }
    }

    /// 重建外部纯文本图书（布局变更后重新排版）。
    func rebuildExternalTextBook() {
        guard let controller = context.controller,
              let textFileURL = controller.textFileURL else { return }
        let restoreLocation = context.currentVisibleLocation() ?? context.persistenceLocation()
        let pageSize = controller.currentTextPageSize()
        let style = controller.currentTextRenderStyle()
        let builder = context.makePlainTextBookBuilder(layoutConfig: controller.currentTextLayoutConfig(pageSize: pageSize))
        if let newBook = try? builder.build(textFileURL: textFileURL, pageSize: pageSize, style: style) {
            context.runtime?.applyTextBook(newBook, restoreLocation: restoreLocation)
        }
    }
}