import Foundation

final class RDEPUBReaderLocationCoordinator {
    private unowned let context: RDEPUBReaderContext

    private var lastPageChangeSpineIndex: Int?

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

    @discardableResult
    func restoreReadingLocation(
        _ location: RDEPUBLocation,
        animated: Bool = false,
        targetHighlightRangeInfo: String? = nil
    ) -> Bool {
        guard let controller = context.controller,
              let readerView = context.readerView else { return false }
        if context.bookPageMap != nil {
            _ = context.runtime?.ensureOnDemandNavigationTargetAvailable(for: location)
        }
        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,
                targetHighlightRangeInfo: targetHighlightRangeInfo
            )
        } else if context.textBook == nil {
            _ = context.readingSession?.queueNavigation(
                to: location,
                relativeToSpineIndex: nil,
                bookIdentifier: context.currentBookIdentifier,
                targetHighlightRangeInfo: targetHighlightRangeInfo
            )
        } else {
            context.readingSession?.transition(to: .jumping)
        }
        readerView.transitionToPage(pageNum: max(targetPageNumber - 1, 0), animated: animated)

        recordPageChangeIfNeeded()

        return true
    }

    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
            }

            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)
    }

    func persistenceLocation() -> RDEPUBLocation? {
        guard let controller = context.controller,
              let currentBookIdentifier = context.currentBookIdentifier else {
            return nil
        }
        return controller.persistence?.loadLocation(for: currentBookIdentifier)
    }

    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.updateReaderChrome()
    }

    func recordPageChangeIfNeeded() {
        guard let runtime = context.runtime,
              let bookPageMap = context.bookPageMap,
              let readerView = context.readerView else { return }

        let currentPageNumber = readerView.currentPage + 1
        guard let currentSpineIndex = bookPageMap.spineIndex(forAbsolutePage: currentPageNumber - 1) else {
            return
        }

        if let lastSpineIndex = lastPageChangeSpineIndex,
           lastSpineIndex != currentSpineIndex {
            runtime.jumpSessionManager.recordPageChange(
                fromSpineIndex: lastSpineIndex,
                toSpineIndex: currentSpineIndex
            )
        }

        lastPageChangeSpineIndex = currentSpineIndex

        let isIdle = context.secondsSinceLastUserNavigation() > 2.0
        if let endReason = runtime.jumpSessionManager.checkSessionEnd(
            currentSpineIndex: currentSpineIndex,
            isIdle: isIdle
        ) {
            runtime.jumpSessionManager.endSession(endReason)
        }
    }

    func resetPageChangeState() {
        lastPageChangeSpineIndex = nil
    }
}