import Foundation

struct RDEPUBResolvedPage {
    let page: RDEPUBTextPage
    let chapter: RDEPUBRuntimeChapter
    let chapterIndex: Int
}

final class RDEPUBPageResolver {
    private unowned let context: RDEPUBReaderContext
    private let store: RDEPUBChapterRuntimeStore

    init(context: RDEPUBReaderContext, store: RDEPUBChapterRuntimeStore) {
        self.context = context
        self.store = store
    }

    func resolvePage(absolutePageIndex: Int) -> RDEPUBResolvedPage? {
        guard let bookPageMap = context.bookPageMap,
              let spineIndex = bookPageMap.spineIndex(forAbsolutePage: absolutePageIndex),
              let localPageIndex = bookPageMap.localPageIndex(forAbsolutePage: absolutePageIndex),
              let chapter = store.chapterData(for: spineIndex),
              chapter.pages.indices.contains(localPageIndex),
              let chapterIndex = bookPageMap.chapterIndex(forSpineIndex: spineIndex) else {
            return nil
        }

        var page = chapter.pages[localPageIndex]
        page.absolutePageIndex = absolutePageIndex
        page.chapterIndex = chapterIndex
        page.pageIndexInChapter = localPageIndex
        page.totalPagesInChapter = chapter.pages.count
        return RDEPUBResolvedPage(page: page, chapter: chapter, chapterIndex: chapterIndex)
    }
}