//
//  MP_CacheManager.swift
//  MusicPlayer
//
//  Created by Mr.Zhou on 2024/5/23.
//

import Foundation
///缓存实体资源
class CachedMedia: NSObject, Codable {
    //数据
    let data: Data
    //数据块
    let dataBlocks:[MediaDataBlock]
    //是否完整
    let isComplete: Bool
    //最大长度
    let maxCount:Int64
    init(data: Data, dataBlocks:[MediaDataBlock], isComplete: Bool, maxCount:Int64) {
        self.data = data
        self.dataBlocks = dataBlocks
        self.isComplete = isComplete
        self.maxCount = maxCount
    }
}
///缓存管理工具
class MP_CacheManager {
    // 单例模式，提供全局访问点
    static let shared = MP_CacheManager()
    // 缓存实体，字典形式，键值1为videoID，键值2为对应的资源数据
    private let memoryCache = NSCache<NSString, CachedMedia>()
    //文件管理器
    private let fileManager = FileManager.default
    //缓存文件地址
    private let cacheDirectory: URL
    //缓存专用线程
    private var cacheQueue = DispatchQueue(label: "com.MP_CacheManager.cacheQueue")
    //缓存专用
    private var cacheOperations: [String: DispatchWorkItem] = [:]
    //专用节流时间间隔
    private let throttleInterval: TimeInterval = 1.0
    //固定缓存时间
    private let expirationInterval: TimeInterval = 86400 // 24小时
    private init() {
        //获取全部文件地址
        let urls = fileManager.urls(for: .cachesDirectory, in: .userDomainMask)
        //设置缓存文件地址
        cacheDirectory = urls[0].appendingPathComponent("MyAssetCacheManager")
        //检查缓存文件地址是否存在
        if !fileManager.fileExists(atPath: cacheDirectory.path) {
            //不存在就创建一个
            try? fileManager.createDirectory(at: cacheDirectory, withIntermediateDirectories: true, attributes: nil)
        }
    }
    
    /// 保存缓存数据
    /// - Parameters:
    ///   - data: 数据本身
    ///   - key: 使用videoId作为对应的键值
    func cacheData(_ data: Data, dataBlocks:[MediaDataBlock], forKey key: String, isComplete: Bool = false, maxCount:Int64) {
        // 在你的 cacheQueue 里执行操作来确保线程安全
        cacheQueue.async { [weak self] in
            // 取消这个 key 的任何现有缓存操作
            self?.cacheOperations[key]?.cancel()
            
            // 创建一个新的缓存操作
            let operation = DispatchWorkItem {
                self?.performCacheData(data, dataBlocks: dataBlocks, forKey: key, isComplete: isComplete, maxCount: maxCount)
                // 甚至删除值也包含在cacheQueue的异步调用中
                self?.cacheQueue.async {
                    self?.cacheOperations.removeValue(forKey: key)
                }
            }
            
            // 把 operation 保存进字典
            self?.cacheOperations[key] = operation
            
            // 安排 operation 在节流间隔后运行
            self?.cacheQueue.asyncAfter(deadline: .now() + self!.throttleInterval, execute: operation)
        }
    }
    //保存缓存数据
    private func performCacheData(_ data: Data, dataBlocks:[MediaDataBlock], forKey key: String, isComplete: Bool = false, maxCount:Int64) {
        let contentToCache = CachedMedia(data: data, dataBlocks: dataBlocks, isComplete: isComplete, maxCount: maxCount)
        memoryCache.setObject(contentToCache, forKey: key as NSString)
        //文件路径
        let fileURL = self.cacheDirectory.appendingPathComponent(key)
        //临时文件
        let tempURL = fileURL.appendingPathExtension("tmp")
        let encoder = JSONEncoder()
        do {
            let newData = try encoder.encode(contentToCache)
            // 写入到文件
            try newData.write(to: tempURL, options: .atomicWrite)
            // 检查目标位置是否已经存在文件，如果存在，则删除
            if self.fileManager.fileExists(atPath: fileURL.path) {
                try self.fileManager.removeItem(at: fileURL)
            }
            // 然后将临时文件移动到最终位置
            try self.fileManager.moveItem(at: tempURL, to: fileURL)
            // 设置过期时间元数据
            let expirationDate = Date().addingTimeInterval(self.expirationInterval)
            try self.fileManager.setAttributes([.modificationDate: expirationDate], ofItemAtPath: fileURL.path)
        } catch {
            // 如果发生错误，删除临时文件
            try? self.fileManager.removeItem(at: tempURL)
            print("无法将密钥数据写入磁盘 \(key) - 错误: \(error)")
        }
    }
    /// 取出数据
    /// - Parameter key: 使用videoId作为对应的键值
    /// - Returns: 返回的数据
    func data(forKey key: String) -> CachedMedia? {
        if let cachedContent = memoryCache.object(forKey: key as NSString){
            return cachedContent
        }
        return cacheQueue.sync {
            [weak self] in
            guard let self = self else { return nil }
            let fileURL = self.cacheDirectory.appendingPathComponent(key)
            guard let jsonData = try? Data(contentsOf: fileURL) else { return nil }
            // 将从磁盘中读取到的 JSON 数据反序列化为 CachedMedia 对象
            let decoder = JSONDecoder()
            do{
                let cachedContent = try decoder.decode(CachedMedia.self, from: jsonData)
                // 检查数据是否过期（同时可以在此处加入完整性检查）
                let attributes = try fileManager.attributesOfItem(atPath: fileURL.path)
                guard let modificationDate = attributes[.modificationDate] as? Date else { return nil }
                if Date().timeIntervalSince(modificationDate) < expirationInterval{
                    // 数据未过期，返回数据并更新内存缓存
                    memoryCache.setObject(cachedContent, forKey: key as NSString)
                    return cachedContent
                } else {
                    // 数据已过期，删除缓存文件
                    try fileManager.removeItem(at: fileURL)
                }
            } catch {
                print("读取缓存数据失败 \(key) - 错误: \(error)")
            }
            return nil
        }
    }
}