import Foundation

/// EPUB 阅读器位置协调器：负责阅读位置的恢复、查询和持久化。
///
/// 职责：
/// - 根据保存的位置恢复阅读进度
/// - 获取当前可见页面的阅读位置
/// - 从持久化存储加载已保存位置
/// - 持久化当前位置并通知委托
final class RDEPUBReaderLocationCoordinator {
    private unowned let context: RDEPUBReaderContext

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

    /// 恢复到指定阅读位置，返回是否成功跳转。
    @discardableResult
    func restoreReadingLocation(_ location: RDEPUBLocation, animated: Bool = false) -> Bool {
        guard let controller = context.controller,
              let readerView = context.readerView else { return false }
        guard let targetPageNumber = controller.pageNumber(for: location) else {
            readerView.transitionToPage(pageNum: 0)
            context.readingSession?.transition(to: .idle)
            return false
        }

        if context.bookPageMap != nil {
            guard context.runtime?.prepareOnDemandChapter(forAbsolutePageNumber: targetPageNumber) == true else {
                return false
            }
            _ = context.readingSession?.queueNavigation(
                to: location,
                relativeToSpineIndex: nil,
                bookIdentifier: context.currentBookIdentifier
            )
        } else if context.textBook == nil {
            _ = context.readingSession?.queueNavigation(
                to: location,
                relativeToSpineIndex: nil,
                bookIdentifier: context.currentBookIdentifier
            )
        } else {
            context.readingSession?.transition(to: .jumping)
        }
        readerView.transitionToPage(pageNum: max(targetPageNumber - 1, 0), animated: animated)
        return true
    }

    /// 获取当前可见页面对应的阅读位置。
    func currentVisibleLocation() -> RDEPUBLocation? {
        guard let controller = context.controller,
              let readerView = context.readerView else {
            return nil
        }
        let pageNumber = readerView.currentPage + 1
        if (context.textBook != nil || context.bookPageMap != nil), readerView.currentPage >= 0 {
            if let location = controller.resolvedTextLocation(forPageNumber: pageNumber) {
                return location
            }
            // resolvedTextLocation 可能因章节数据未加载而返回 nil，
            // 通过 readingSession 的 activePages 构建回退位置
            if let readingSession = context.readingSession,
               readingSession.activePages.indices.contains(readerView.currentPage) {
                return readingSession.fallbackLocation(
                    for: readingSession.activePages[readerView.currentPage],
                    bookIdentifier: context.currentBookIdentifier
                )
            }
        }
        return context.readingSession?.currentReadingLocation(bookIdentifier: context.currentBookIdentifier)
    }

    /// 从持久化存储加载上次保存的阅读位置。
    func persistenceLocation() -> RDEPUBLocation? {
        guard let controller = context.controller,
              let currentBookIdentifier = context.currentBookIdentifier else {
            return nil
        }
        return controller.persistence?.loadLocation(for: currentBookIdentifier)
    }

    /// 持久化阅读位置，并通知委托更新目录项和书签状态。
    func persist(location: RDEPUBLocation) {
        guard let controller = context.controller,
              let currentBookIdentifier = context.currentBookIdentifier else { return }
        controller.persistence?.saveLocation(location, for: currentBookIdentifier)
        controller.delegate?.epubReader(controller, didUpdateLocation: location)
        controller.delegate?.epubReader(controller, didUpdateCurrentTableOfContentsItem: controller.currentTableOfContentsItem)
        controller.updateBookmarkChrome()
    }
}