import Foundation

/// 上传任务映射持久化（P3 计划 Task 8）。
///
/// `taskId → {注册参数, URLSession taskIdentifier, 执行计数}` 存 Application
/// Support 下 plist；对应 Android 侧 taskId→workId 映射由 WorkManager 自持
/// 的职责——iOS 无系统级自持映射，改为本插件显式落盘：
///
/// - App 被系统在后台拉起（或用户重启）后，`getAllTasks` 返回的系统任务经
///   taskIdentifier 反查 taskId，重挂事件归属（技术方案 §6.2「重新启动时
///   重连系统会话并校准本地任务」）；
/// - 仅存映射所需最小字段；进度快照不落盘（重联后 didSendBodyData 会
///   继续产生新进度）。
///
/// 线程模型：通道回调在主线程、session delegate 在后台队列访问——全部
/// 经 [lock] 串行化；写盘频率低（注册/终态/取消），同步写原子 plist。
final class UploadTaskStore {

    /// 单条任务映射（plist 可序列化字段）。
    struct Entry {
        var url: String
        var method: String
        var headers: [String: String]
        var filePath: String
        var uploadId: String?
        var attempt: Int
        /// 已执行传输次数（含首发；镜像 Kotlin MAX_WORK_ATTEMPTS 语义）。
        var executions: Int
        /// 对应 URLSessionTask.taskIdentifier（-1 = 尚未创建系统任务）。
        var sessionTaskIdentifier: Int
    }

    private let lock = NSLock()
    private let fileURL: URL
    private var entries: [String: Entry] = [:]

    init(directory: URL? = nil, fileName: String = "upload-task-map.plist") {
        let dir =
            directory
            ?? FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
            .appendingPathComponent("PhotoLiveUploads", isDirectory: true)
        try? FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)
        fileURL = dir.appendingPathComponent(fileName)
        if let raw = NSDictionary(contentsOf: fileURL) as? [String: [String: Any]] {
            entries = raw.mapValues { Entry(plist: $0) }
        }
    }

    // ── 读写 API（锁内） ──────────────────────────────────────────────

    func entry(taskId: String) -> Entry? {
        lock.lock()
        defer { lock.unlock() }
        return entries[taskId]
    }

    func taskId(sessionTaskIdentifier: Int) -> String? {
        lock.lock()
        defer { lock.unlock() }
        return entries.first { $0.value.sessionTaskIdentifier == sessionTaskIdentifier }?.key
    }

    func allTaskIds() -> [String] {
        lock.lock()
        defer { lock.unlock() }
        return Array(entries.keys)
    }

    func upsert(taskId: String, entry: Entry) {
        lock.lock()
        entries[taskId] = entry
        persistLocked()
        lock.unlock()
    }

    /// 原地修改并落盘（不存在则忽略）。
    func mutate(taskId: String, _ transform: (inout Entry) -> Void) {
        lock.lock()
        guard var entry = entries[taskId] else {
            lock.unlock()
            return
        }
        transform(&entry)
        entries[taskId] = entry
        persistLocked()
        lock.unlock()
    }

    func remove(taskId: String) {
        lock.lock()
        entries.removeValue(forKey: taskId)
        persistLocked()
        lock.unlock()
    }

    // ── plist 编解码 ─────────────────────────────────────────────────

    private func persistLocked() {
        let raw = entries.mapValues { $0.asPlist() } as NSDictionary
        raw.write(to: fileURL, atomically: true)
    }
}

private extension UploadTaskStore.Entry {
    init(plist raw: [String: Any]) {
        self.init(
            url: raw["url"] as? String ?? "",
            method: raw["method"] as? String ?? "PUT",
            headers: (raw["headers"] as? [String: String]) ?? [:],
            filePath: raw["filePath"] as? String ?? "",
            uploadId: raw["uploadId"] as? String,
            attempt: (raw["attempt"] as? NSNumber)?.intValue ?? 0,
            executions: (raw["executions"] as? NSNumber)?.intValue ?? 1,
            sessionTaskIdentifier: (raw["sessionTaskIdentifier"] as? NSNumber)?.intValue ?? -1
        )
    }

    func asPlist() -> [String: Any] {
        [
            "url": url,
            "method": method,
            "headers": headers,
            "filePath": filePath,
            "uploadId": uploadId ?? "",
            "attempt": attempt,
            "executions": executions,
            "sessionTaskIdentifier": sessionTaskIdentifier,
        ]
    }
}