ReadViewSDK/Sources/RDReaderView/EPUBUI/RDEPUBReaderController+LocationResolution.swift

import UIKit

extension RDEPUBReaderController {

    func pageNumber(for location: RDEPUBLocation, rangeInfo: String? = nil) -> Int? {
        if let publication,
           let bookPageMap = readerContext.bookPageMap,
           let spineIndex = readerContext.normalizedSpineIndex(for: location),
           let entry = bookPageMap.entry(forSpineIndex: spineIndex) {
            let normalizedLocation = publication.resourceResolver.normalizedLocation(
                location,
                relativeToSpineIndex: nil,
                bookIdentifier: currentBookIdentifier
            ) ?? location
            let localPageIndex = resolvedLocalPageIndex(
                for: normalizedLocation,
                spineIndex: spineIndex,
                fallbackEntry: entry,
                rangeInfo: rangeInfo
            ) ?? fallbackLocalPageIndex(for: normalizedLocation, pageCount: entry.pageCount)
            return bookPageMap.absolutePageIndex(
                spineIndex: spineIndex,
                localPageIndex: min(max(localPageIndex, 0), max(entry.pageCount - 1, 0))
            ).map { $0 + 1 }
        }

        if let textBook {
            let normalizedLocation = publication?.resourceResolver.normalizedLocation(
                location,
                relativeToSpineIndex: nil,
                bookIdentifier: currentBookIdentifier
            ) ?? location

            if let pageNumber = pageNumberFromRangeInfo(rangeInfo, in: textBook, matching: normalizedLocation) {
                return pageNumber
            }

            if let anchor = normalizedLocation.rangeAnchor?.start {
                if let page = textBook.indexTable.pageNumber(for: anchor, in: textBook) {
                    return page + 1
                }
            }

            if let publication {
                return textBook.pageNumber(
                    for: normalizedLocation,
                    resolver: publication.resourceResolver,
                    bookIdentifier: currentBookIdentifier
                )
            }
            // External text books have no resolver; hrefs match verbatim.
            return textBook.chapterData(for: normalizedLocation.href)?
                .pageNumber(for: normalizedLocation)
        }

        return readingSession?.queueNavigation(
            to: location,
            relativeToSpineIndex: nil,
            bookIdentifier: currentBookIdentifier
        )
    }

    func resolvedTextLocation(forPageNumber pageNumber: Int) -> RDEPUBLocation? {
        if let resolvedPage = resolvedRuntimePage(forPageNumber: pageNumber) {
            let startOffset = resolvedPage.page.pageStartOffset
            let endOffset = max(startOffset, resolvedPage.page.pageEndOffset)
            let chapterData = makeRuntimeChapterData(from: resolvedPage)
            let location = chapterData.location(
                for: NSRange(location: startOffset, length: max(endOffset - startOffset + 1, 1)),
                bookIdentifier: currentBookIdentifier
            )
            if let publication {
                return publication.resourceResolver.normalizedLocation(
                    location,
                    relativeToSpineIndex: nil,
                    bookIdentifier: currentBookIdentifier
                ) ?? location
            }
            return location
        }

        guard let textBook,
              let page = textBook.page(at: pageNumber) else {
            return nil
        }

        let location = textBook.chapterData(forPageNumber: pageNumber)?.location(forPage: page, bookIdentifier: currentBookIdentifier)
            ?? textBook.location(forPageNumber: pageNumber, bookIdentifier: currentBookIdentifier)
        guard let location else { return nil }

        if let publication {
            return publication.resourceResolver.normalizedLocation(
                location,
                relativeToSpineIndex: nil,
                bookIdentifier: currentBookIdentifier
            ) ?? location
        }
        return location
    }

    func currentVisibleRangeInfo() -> String? {
        guard let pageNumber = currentPageNumber else {
            return nil
        }

        if let resolvedPage = resolvedRuntimePage(forPageNumber: pageNumber) {
            let startOffset = resolvedPage.page.pageStartOffset
            let endOffset = max(startOffset + 1, resolvedPage.page.pageEndOffset + 1)
            return RDEPUBTextOffsetRangeInfo(
                href: resolvedPage.chapter.href,
                start: startOffset,
                end: endOffset
            ).jsonString()
        }

        guard let textBook,
              let page = textBook.page(at: pageNumber) else {
            return nil
        }

        let startOffset = page.pageStartOffset
        let endOffset = max(startOffset + 1, page.pageEndOffset + 1)
        return RDEPUBTextOffsetRangeInfo(
            href: page.href,
            start: startOffset,
            end: endOffset
        ).jsonString()
    }

    func synchronizeTextReadingState(pageNumber: Int, location: RDEPUBLocation) {
        if let resolvedPage = resolvedRuntimePage(forPageNumber: pageNumber) {
            readingSession?.updateReadingContext(
                pageNumber: pageNumber,
                location: location,
                spineIndex: resolvedPage.page.spineIndex,
                chapterIndex: resolvedPage.chapterIndex,
                bookIdentifier: currentBookIdentifier
            )
            return
        }

        guard let textBook,
              let page = textBook.page(at: pageNumber) else {
            return
        }

        readingSession?.updateReadingContext(
            pageNumber: pageNumber,
            location: location,
            spineIndex: page.spineIndex,
            chapterIndex: page.chapterIndex,
            bookIdentifier: currentBookIdentifier
        )
    }

    func nativeTextSnapshot(from textBook: RDEPUBTextBook) -> RDEPUBNativeTextSnapshot {
        let chapters = textBook.chapterInfos
        let pages = textBook.pages.map {
            EPUBPage(
                spineIndex: $0.spineIndex,
                chapterIndex: $0.chapterIndex,
                pageIndexInChapter: $0.pageIndexInChapter,
                totalPagesInChapter: $0.totalPagesInChapter,
                chapterTitle: $0.chapterTitle,
                fixedSpread: nil
            )
        }
        return (pages, chapters)
    }

    func chapterOffset(for location: RDEPUBLocation, fallbackEntry: RDEPUBBookPageMapEntry, rangeInfo: String? = nil) -> Int {
        if let decodedRangeInfo = decodedRangeInfo(from: rangeInfo, matching: location) {
            return decodedRangeInfo.start
        }
        // Native text anchors carry the exact UTF-16 chapter offset and remain
        // stable across font/layout changes. Prefer them over CFI recovery,
        // which may temporarily resolve to the chapter's first marker while a
        // new CFI map is still being prepared.
        if let anchor = location.rangeAnchor?.start {
            return anchor.chapterOffset
        }
        if let spineIndex = readerContext.normalizedSpineIndex(for: location),
           let runtimeChapter = runtime.chapterRuntimeStore.chapterData(for: spineIndex),
           let cfi = primaryLocationCFI(for: location),
           let offset = runtimeChapter.chapterOffsetMap.chapterOffset(forCFI: cfi) {
            return offset
        }
        if let rawCFI = primaryLocationCFI(for: location),
           let cfi = RDEPUBCFICompatibility.parseLossy(rawCFI),
           let cfiOffset = RDEPUBCFIResolver.resolve(cfi).chapterOffset {
            return cfiOffset
        }
        if let fragment = location.fragment,
           let offset = fallbackEntry.fragmentOffsets[fragment] {
            return offset
        }
        return 0
    }

    func fallbackLocalPageIndex(for location: RDEPUBLocation, pageCount: Int) -> Int {
        guard pageCount > 1 else { return 0 }
        return min(
            pageCount - 1,
            max(0, Int(round(location.navigationProgression * Double(pageCount - 1))))
        )
    }

    private func resolvedRuntimePage(forPageNumber pageNumber: Int) -> RDEPUBResolvedPage? {
        runtime.pageResolver.resolvePage(absolutePageIndex: pageNumber - 1)
    }

    private func resolvedLocalPageIndex(
        for location: RDEPUBLocation,
        spineIndex: Int,
        fallbackEntry: RDEPUBBookPageMapEntry,
        rangeInfo: String? = nil
    ) -> Int? {
        let offset = chapterOffset(for: location, fallbackEntry: fallbackEntry, rangeInfo: rangeInfo)

        if let runtimeChapter = runtime.chapterRuntimeStore.chapterData(for: spineIndex),
           let pageIndex = runtimeChapter.chapterOffsetMap.pageIndex(forChapterOffset: offset) {
            return pageIndex
        }

        if let summary = readerContext.chapterSummary(forSpineIndex: spineIndex) {
            return summary.pageRanges.firstIndex {
                let range = $0.nsRange
                return offset >= range.location && offset <= max(range.location + range.length - 1, range.location)
            }
        }

        return nil
    }

    private func primaryLocationCFI(for location: RDEPUBLocation) -> String? {
        if let rangeCFI = RDEPUBCFICompatibility.parseRangeLossy(location.rangeCFI) {
            return rangeCFI.start.rawValue
        }
        return location.cfi
    }

    private func pageNumberFromRangeInfo(
        _ rangeInfo: String?,
        in textBook: RDEPUBTextBook,
        matching location: RDEPUBLocation
    ) -> Int? {
        guard let decodedRangeInfo = decodedRangeInfo(from: rangeInfo, matching: location),
              let chapterData = chapterData(in: textBook, for: decodedRangeInfo),
              let page = chapterData.page(containing: decodedRangeInfo.start) else {
            return nil
        }
        return page.absolutePageIndex + 1
    }

    private func decodedRangeInfo(
        from rangeInfo: String?,
        matching location: RDEPUBLocation
    ) -> RDEPUBTextOffsetRangeInfo? {
        guard let decodedRangeInfo = RDEPUBTextOffsetRangeInfo.decode(from: rangeInfo),
              normalizedHref(decodedRangeInfo.href) == normalizedHref(location.href) else {
            return nil
        }
        return decodedRangeInfo
    }

    private func chapterData(
        in textBook: RDEPUBTextBook,
        for rangeInfo: RDEPUBTextOffsetRangeInfo
    ) -> RDEPUBChapterData? {
        if let chapterData = textBook.chapterData(for: rangeInfo.href) {
            return chapterData
        }

        let targetHref = normalizedHref(rangeInfo.href)
        if let chapterData = textBook.chapterData(for: targetHref) {
            return chapterData
        }

        guard let chapter = textBook.chapters.first(where: { normalizedHref($0.href) == targetHref }) else {
            return nil
        }
        return textBook.chapterData(for: chapter.href)
    }

    private func normalizedHref(_ href: String) -> String {
        publication?.resourceResolver.normalizedHref(href)
            ?? href.components(separatedBy: "#").first
            ?? href
    }

    private func nearestFragmentID(beforeOrAt offset: Int, fragmentOffsets: [String: Int]) -> String? {
        var bestID: String?
        var bestOffset = Int.min
        for (fragmentID, fragmentOffset) in fragmentOffsets where fragmentOffset <= offset && fragmentOffset > bestOffset {
            bestOffset = fragmentOffset
            bestID = fragmentID
        }
        return bestID
    }

    private func makeRuntimeChapterData(from resolvedPage: RDEPUBResolvedPage) -> RDEPUBChapterData {
        let textChapter = RDEPUBTextChapter(
            chapterIndex: resolvedPage.chapterIndex,
            spineIndex: resolvedPage.chapter.spineIndex,
            href: resolvedPage.chapter.href,
            title: resolvedPage.chapter.title,
            attributedContent: resolvedPage.chapter.typesetAttributedString,
            fragmentOffsets: resolvedPage.chapter.chapterOffsetMap.fragmentOffsets,
            cfiMap: resolvedPage.chapter.chapterOffsetMap.cfiMap,
            pageBreakReasons: resolvedPage.chapter.pages.map(\.metadata.breakReason),
            pages: resolvedPage.chapter.pages
        )
        return RDEPUBChapterData(
            chapter: textChapter,
            indexTable: RDEPUBTextIndexTable(chapters: [textChapter])
        )
    }
}