import Foundation

final class RDEPUBChapterSummaryDiskCache {
    private let cacheDirectory: URL
    private let fileManager = FileManager.default
    private let queue = DispatchQueue(label: "com.rdreader.summarydiskcache", qos: .utility)

    init(cacheDirectory: URL) {
        self.cacheDirectory = cacheDirectory
        try? fileManager.createDirectory(at: cacheDirectory, withIntermediateDirectories: true)
    }

    // MARK: - 写入（异步）

    func write(summary: RDEPUBChapterSummary, for key: RDEPUBChapterCacheKey) {
        queue.async {
            self.writeImmediately(summary: summary, for: key)
        }
    }

    /// 同步写入：用于后台整书元数据构建完成前，确保摘要文件已经真实落盘。
    func writeSynchronously(summary: RDEPUBChapterSummary, for key: RDEPUBChapterCacheKey) {
        queue.sync {
            self.writeImmediately(summary: summary, for: key)
        }
    }

    /// 等待此前已排队的异步写入全部落盘。
    func flushPendingWrites() {
        queue.sync { }
    }

    // MARK: - 读取（同步，因为 loadChapter 已在串行队列上）

    func read(for key: RDEPUBChapterCacheKey) -> RDEPUBChapterSummary? {
        let fileURL = self.fileURL(for: key)
        let data: Data
        do {
            data = try Data(contentsOf: fileURL)
        } catch {
            let nsError = error as NSError
            if nsError.domain == NSCocoaErrorDomain && nsError.code == NSFileReadNoSuchFileError {
                // 文件不存在属于正常缓存未命中，不报错
            } else {
                #if DEBUG
                print("[RDEPUBChapterSummaryDiskCache] ⚠️ read IO error for \(fileURL.lastPathComponent): \(error.localizedDescription)")
                #endif
            }
            return nil
        }
        do {
            return try JSONDecoder().decode(RDEPUBChapterSummary.self, from: data)
        } catch {
            #if DEBUG
            print("[RDEPUBChapterSummaryDiskCache] ⚠️ decode error for \(fileURL.lastPathComponent): \(error.localizedDescription)")
            #endif
            return nil
        }
    }

    // MARK: - 批量读取：二次打开时直接从磁盘构建 BookPageMap

    /// 批量读取指定缓存键列表的摘要，返回 spineIndex → summary 映射。
    /// 同步方法，应在后台线程调用。
    /// 由调用方负责构建完整的缓存键列表（含正确的 contentHash）。
    func readAll(keys: [(key: RDEPUBChapterCacheKey, spineIndex: Int, href: String, title: String)]) -> (
        summaries: [Int: RDEPUBChapterSummary],
        mapBuilder: RDEPUBBookPageMap.Builder
    ) {
        var summaries: [Int: RDEPUBChapterSummary] = [:]
        var mapBuilder = RDEPUBBookPageMap.Builder()

        for item in keys {
            if let summary = read(for: item.key) {
                summaries[item.spineIndex] = summary
                mapBuilder.add(
                    spineIndex: item.spineIndex,
                    href: item.href,
                    title: item.title,
                    pageCount: summary.pageCount,
                    fragmentOffsets: summary.fragmentOffsets
                )
            }
        }
        return (summaries, mapBuilder)
    }

    /// 检查指定缓存键列表是否全部有对应的磁盘摘要。
    func isCacheComplete(keys: [RDEPUBChapterCacheKey]) -> Bool {
        for key in keys {
            if read(for: key) == nil {
                return false
            }
        }
        return true
    }

    /// 清空所有缓存文件
    func removeAll() {
        removeFiles(matching: { _ in true })
    }

    /// 清空指定书籍的所有缓存文件
    func removeAll(forBookID bookID: String) {
        let bookPrefix = Self.cacheNamespacePrefix(for: bookID)
        removeFiles { $0.hasPrefix(bookPrefix + "__") }
    }

    /// 清空指定渲染签名下的所有缓存文件
    func removeAll(forRenderSignature renderSignature: String) {
        let renderPrefix = "__" + Self.cacheNamespacePrefix(for: renderSignature) + "__"
        removeFiles { $0.contains(renderPrefix) }
    }

    /// 缓存统计信息
    var cacheStatistics: (fileCount: Int, totalBytes: Int64) {
        guard let files = try? fileManager.contentsOfDirectory(at: cacheDirectory, includingPropertiesForKeys: [.fileSizeKey]) else {
            return (0, 0)
        }
        var count = 0
        var totalBytes: Int64 = 0
        for fileURL in files where fileURL.pathExtension == "json" {
            count += 1
            if let size = try? fileURL.resourceValues(forKeys: [.fileSizeKey]).fileSize {
                totalBytes += Int64(size)
            }
        }
        return (count, totalBytes)
    }

    // MARK: - key -> 文件路径

    /// 使用确定性字符串拼接生成文件名，不依赖 Hashable.hashValue
    private func fileURL(for key: RDEPUBChapterCacheKey) -> URL {
        let bookPrefix = Self.cacheNamespacePrefix(for: key.bookID)
        let renderPrefix = Self.cacheNamespacePrefix(for: key.renderSignature)
        let rawKey = "\(key.bookID)_\(key.spineIndex)_\(key.renderSignature)_\(key.chapterContentHash)"
        let digest = rawKey.sha256Hex
        return cacheDirectory.appendingPathComponent("\(bookPrefix)__\(renderPrefix)__\(digest).json")
    }

    private func writeImmediately(summary: RDEPUBChapterSummary, for key: RDEPUBChapterCacheKey) {
        let fileURL = self.fileURL(for: key)
        let tmpURL = fileURL.appendingPathExtension("tmp")
        do {
            let data = try JSONEncoder().encode(summary)
            try data.write(to: tmpURL)
            if fileManager.fileExists(atPath: fileURL.path) {
                _ = try fileManager.replaceItemAt(fileURL, withItemAt: tmpURL)
            } else {
                try fileManager.moveItem(at: tmpURL, to: fileURL)
            }
        } catch {
            #if DEBUG
            print("[RDEPUBChapterSummaryDiskCache] ⚠️ write error for \(fileURL.lastPathComponent): \(error.localizedDescription)")
            #endif
            try? fileManager.removeItem(at: tmpURL)
        }
    }

    private func removeFiles(matching predicate: (String) -> Bool) {
        guard let files = try? fileManager.contentsOfDirectory(at: cacheDirectory, includingPropertiesForKeys: nil) else { return }
        for fileURL in files where fileURL.pathExtension == "json" && predicate(fileURL.lastPathComponent) {
            try? fileManager.removeItem(at: fileURL)
        }
    }

    private static func cacheNamespacePrefix(for rawValue: String) -> String {
        rawValue.sha256Hex.prefix(12).lowercased()
    }
}

struct RDEPUBChapterSummary: Codable {
    let pageRanges: [RangeData]
    let pageCount: Int
    let fragmentOffsets: [String: Int]
    let renderSignature: String
    let schemaVersion: Int
    let chapterContentHash: String
    let pageMetadataList: [PageMetadataSummary]

    static let currentSchemaVersion = 6

    struct RangeData: Codable {
        let location: Int
        let length: Int
        var nsRange: NSRange { NSRange(location: location, length: length) }
    }

    struct PageMetadataSummary: Codable {
        let breakReason: String
        let attachmentRanges: [RangeData]
        let attachmentKinds: [String]
        let blockKinds: [String]
        let semanticHints: [String]
        let attachmentPlacements: [String]
        let trailingFragmentID: String?

        func toPageMetadata() -> RDEPUBTextPageMetadata {
            RDEPUBTextPageMetadata(
                breakReason: RDEPUBTextPageBreakReason(rawValue: breakReason) ?? .frameLimit,
                blockRange: nil,
                attachmentRanges: attachmentRanges.map { $0.nsRange },
                attachmentKinds: attachmentKinds.compactMap { RDEPUBTextAttachmentKind(rawValue: $0) },
                blockKinds: blockKinds.compactMap { RDEPUBTextBlockKind(rawValue: $0) },
                semanticHints: semanticHints.compactMap { RDEPUBTextSemanticHint(rawValue: $0) },
                attachmentPlacements: attachmentPlacements.compactMap { RDEPUBTextAttachmentPlacement(rawValue: $0) },
                trailingFragmentID: trailingFragmentID,
                diagnostics: []
            )
        }

        static func from(_ metadata: RDEPUBTextPageMetadata) -> PageMetadataSummary {
            PageMetadataSummary(
                breakReason: metadata.breakReason.rawValue,
                attachmentRanges: metadata.attachmentRanges.map { .init(location: $0.location, length: $0.length) },
                attachmentKinds: metadata.attachmentKinds.map { $0.rawValue },
                blockKinds: metadata.blockKinds.map { $0.rawValue },
                semanticHints: metadata.semanticHints.map { $0.rawValue },
                attachmentPlacements: metadata.attachmentPlacements.map { $0.rawValue },
                trailingFragmentID: metadata.trailingFragmentID
            )
        }
    }
}