import Foundation

// MARK: - 持久化协议

/// 阅读器持久化协议
/// 定义了阅读位置、书签、高亮和用户设置的存储接口
/// 调用方可实现此协议以对接自定义存储（如数据库、云端同步等）
public protocol RDEPUBReaderPersistence: AnyObject {
    /// 加载指定书籍的上次阅读位置
    /// - Parameter bookIdentifier: 书籍唯一标识符
    /// - Returns: 保存的阅读位置，nil 表示首次打开
    func loadLocation(for bookIdentifier: String) -> RDEPUBLocation?

    /// 保存指定书籍的当前阅读位置
    /// - Parameters:
    ///   - location: 阅读位置
    ///   - bookIdentifier: 书籍唯一标识符
    func saveLocation(_ location: RDEPUBLocation, for bookIdentifier: String)

    /// 加载指定书籍的所有书签
    func loadBookmarks(for bookIdentifier: String) -> [RDEPUBBookmark]

    /// 保存指定书籍的所有书签
    func saveBookmarks(_ bookmarks: [RDEPUBBookmark], for bookIdentifier: String)

    /// 加载指定书籍的所有高亮标注
    func loadHighlights(for bookIdentifier: String) -> [RDEPUBHighlight]

    /// 保存指定书籍的所有高亮标注
    func saveHighlights(_ highlights: [RDEPUBHighlight], for bookIdentifier: String)

    /// 加载全局阅读器用户设置（字号、行距、主题等）
    func loadReaderSettings() -> RDEPUBReaderSettings?

    /// 保存全局阅读器用户设置
    func saveReaderSettings(_ settings: RDEPUBReaderSettings)
}

// MARK: - 默认实现

/// 协议的默认空实现，书签/高亮/设置为可选功能
/// DEBUG 模式下会对 no-op 行为输出警告，便于发现未对接持久化层的误用
public extension RDEPUBReaderPersistence {
    func loadBookmarks(for bookIdentifier: String) -> [RDEPUBBookmark] {
        #if DEBUG
        print("[RDEPUBReaderPersistence] ⚠️ loadBookmarks called on default no-op implementation for: \(bookIdentifier)")
        #endif
        return []
    }

    func saveBookmarks(_ bookmarks: [RDEPUBBookmark], for bookIdentifier: String) {
        #if DEBUG
        print("[RDEPUBReaderPersistence] ⚠️ saveBookmarks(\(bookmarks.count) items) called on default no-op implementation for: \(bookIdentifier)")
        #endif
    }

    func loadReaderSettings() -> RDEPUBReaderSettings? {
        #if DEBUG
        print("[RDEPUBReaderPersistence] ⚠️ loadReaderSettings called on default no-op implementation")
        #endif
        return nil
    }

    func saveReaderSettings(_ settings: RDEPUBReaderSettings) {
        #if DEBUG
        print("[RDEPUBReaderPersistence] ⚠️ saveReaderSettings called on default no-op implementation")
        #endif
    }
}

// MARK: - UserDefaults 持久化实现

/// 基于 UserDefaults 的持久化实现
/// 数据以 JSON 格式存储，按书籍标识符分隔存储位置
/// 适合轻量级场景，大量数据建议改用 SQLite 或文件系统
public final class RDEPUBUserDefaultsPersistence: RDEPUBReaderPersistence {
    /// UserDefaults 实例
    private let defaults: UserDefaults
    /// 阅读位置的 key 前缀
    private let locationPrefix: String
    /// 书签列表的 key 前缀
    private let bookmarksPrefix: String
    /// 高亮列表的 key 前缀
    private let highlightsPrefix: String
    /// 用户设置的 key
    private let settingsKey: String

    /// 初始化 UserDefaults 持久化策略
    /// - Parameters:
    ///   - defaults: UserDefaults 实例，默认 .standard
    ///   - locationPrefix: 阅读位置 key 前缀
    ///   - bookmarksPrefix: 书签 key 前缀
    ///   - highlightsPrefix: 高亮 key 前缀
    ///   - settingsKey: 用户设置 key
    public init(
        defaults: UserDefaults = .standard,
        locationPrefix: String = "ssreader.epub.location.",
        bookmarksPrefix: String = "ssreader.epub.bookmarks.",
        highlightsPrefix: String = "ssreader.epub.highlights.",
        settingsKey: String = "ssreader.epub.settings"
    ) {
        self.defaults = defaults
        self.locationPrefix = locationPrefix
        self.bookmarksPrefix = bookmarksPrefix
        self.highlightsPrefix = highlightsPrefix
        self.settingsKey = settingsKey
    }

    public func loadLocation(for bookIdentifier: String) -> RDEPUBLocation? {
        guard let data = defaults.data(forKey: locationPrefix + bookIdentifier) else {
            return nil
        }
        return try? JSONDecoder().decode(RDEPUBLocation.self, from: data)
    }

    public func saveLocation(_ location: RDEPUBLocation, for bookIdentifier: String) {
        guard let data = try? JSONEncoder().encode(location) else {
            return
        }
        defaults.set(data, forKey: locationPrefix + bookIdentifier)
    }

    public func loadBookmarks(for bookIdentifier: String) -> [RDEPUBBookmark] {
        guard let data = defaults.data(forKey: bookmarksPrefix + bookIdentifier) else {
            return []
        }
        return (try? JSONDecoder().decode([RDEPUBBookmark].self, from: data)) ?? []
    }

    public func saveBookmarks(_ bookmarks: [RDEPUBBookmark], for bookIdentifier: String) {
        guard let data = try? JSONEncoder().encode(bookmarks) else {
            return
        }
        defaults.set(data, forKey: bookmarksPrefix + bookIdentifier)
    }

    public func loadHighlights(for bookIdentifier: String) -> [RDEPUBHighlight] {
        guard let data = defaults.data(forKey: highlightsPrefix + bookIdentifier) else {
            return []
        }
        return (try? JSONDecoder().decode([RDEPUBHighlight].self, from: data)) ?? []
    }

    public func saveHighlights(_ highlights: [RDEPUBHighlight], for bookIdentifier: String) {
        guard let data = try? JSONEncoder().encode(highlights) else {
            return
        }
        if data.count > 1_048_576 {
            #if DEBUG
            print("[RDEPUBUserDefaultsPersistence] ⚠️ saveHighlights data size (\(data.count) bytes) exceeds 1MB for: \(bookIdentifier)")
            #endif
        }
        defaults.set(data, forKey: highlightsPrefix + bookIdentifier)
    }

    public func loadReaderSettings() -> RDEPUBReaderSettings? {
        guard let data = defaults.data(forKey: settingsKey) else {
            return nil
        }
        return try? JSONDecoder().decode(RDEPUBReaderSettings.self, from: data)
    }

    public func saveReaderSettings(_ settings: RDEPUBReaderSettings) {
        guard let data = try? JSONEncoder().encode(settings) else {
            return
        }
        defaults.set(data, forKey: settingsKey)
    }
}