import UIKit

/// Keeps pagination cache key generation and cache IO in one BuildPipeline role.
struct RDEPUBPaginationCacheCoordinator {
    private let cache: RDEPUBTextBookCache?
    private let layoutConfig: RDEPUBTextLayoutConfig

    init(cache: RDEPUBTextBookCache?, layoutConfig: RDEPUBTextLayoutConfig) {
        self.cache = cache
        self.layoutConfig = layoutConfig
    }

    func cacheKey(
        bookID: String,
        pageSize: CGSize,
        style: RDEPUBTextRenderStyle
    ) -> String? {
        guard let cache else { return nil }
        return cache.cacheKey(
            bookID: bookID,
            fontSize: style.font.pointSize,
            lineHeightMultiple: style.lineSpacing,
            contentInsets: layoutConfig.edgeInsets,
            pageSize: pageSize,
            layoutConfigSignature: "\(layoutConfig.cacheSignature)|font=\(style.font.fontName)"
        )
    }

    func load(key: String?) -> [String: RDEPUBTextChapterPaginationCache]? {
        key.flatMap { cache?.load(key: $0) }
    }

    func save(chapters: [RDEPUBTextChapter], key: String?) {
        guard let key else { return }
        let paginationCache = chapters.map { chapter in
            RDEPUBTextChapterPaginationCache(
                href: chapter.href,
                pageRanges: chapter.pages.map(\.contentRange),
                breakReasons: chapter.pages.map(\.metadata.breakReason),
                semanticHints: Array(Set(chapter.pages.flatMap(\.metadata.semanticHints)))
            )
        }
        cache?.save(paginationCache, key: key)
    }
}