import Foundation

/// 上传事件总线（session delegate → EventChannel，P3 计划 Task 8）。
///
/// 与 Android 侧 `UploadEventBus.kt` 同语义：
/// - 事件带单调 seq；**终态**（completed / needsRenew / failed）在 Dart
///   ack 前缓存（上限 [maxBuffered]，超出丢最老），EventChannel 重新
///   listen 时重放——App 切后台恢复 / 引擎重建后不丢完成信号；
/// - 进度事件瞬态，不缓存不重放；
/// - 任务重新注册（renew 换 URL）或取消时 [purgeTask] 作废其缓存终态。
///
/// **进程死亡语义（iOS 增强并落盘）**：iOS 后台会话完成后系统可能在后台
/// 拉起 App（Dart 引擎未启动、无人监听事件）投递回调——终态事件除内存
/// 缓存外同步持久化到 Application Support plist（seq 计数器随行），下次
/// 进程内 EventChannel onListen 时一并重放（技术方案 §6.2「传输完成后
/// 持久记录原生回调」）。Android 侧等价场景由 WorkManager 自持任务、
/// 进程重启后 worker 重跑再发事件，无需落盘。
///
/// 事件负载为 [String: Any] 字典：null 值（etag/status 等）以 NSNull 表达
/// ——Flutter 标准编解码两侧均映射为 Dart null，与 Kotlin 显式 null 等价。
///
/// 线程模型：emit 可来自 session delegate 的后台队列；sink 由插件层包装
/// 为主线程投递（EventChannel 契约）。投递在锁内进行——sink 实现为非
/// 阻塞 DispatchQueue.main.async，锁内投递保证 seq 顺序。
final class UploadEventBus {

    static let shared = UploadEventBus()

    /// 缓存终态上限（防无限增长；超量丢最老——极端下 Dart 用 queryTask 校准）。
    static let maxBuffered = 200

    private let lock = NSLock()
    private var sink: (([String: Any]) -> Void)?
    private var seqGen = 0
    private var unacked: [[String: Any]] = []
    private let fileURL: URL

    init(directory: URL? = nil) {
        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("upload-unacked-events.plist")
        loadPersisted()
    }

    // ── 事件出口（镜像 Kotlin UploadEventBus） ───────────────────────

    func emitProgress(taskId: String, sent: Int64, total: Int64) {
        emit(
            [
                "event": UploadBridge.eventProgress,
                "taskId": taskId,
                "sent": NSNumber(value: sent),
                "total": NSNumber(value: total),
            ],
            terminal: false
        )
    }

    func emitCompleted(taskId: String, etag: String?) {
        emit(
            [
                "event": UploadBridge.eventCompleted,
                "taskId": taskId,
                "etag": etag ?? NSNull(),
            ],
            terminal: true
        )
    }

    func emitNeedsRenew(taskId: String) {
        emit(
            [
                "event": UploadBridge.eventNeedsRenew,
                "taskId": taskId,
            ],
            terminal: true
        )
    }

    func emitFailed(taskId: String, code: String, status: Int? = nil) {
        emit(
            [
                "event": UploadBridge.eventFailed,
                "taskId": taskId,
                "code": code,
                "status": status.map { NSNumber(value: $0) } ?? NSNull(),
            ],
            terminal: true
        )
    }

    private func emit(_ event: [String: Any], terminal: Bool) {
        lock.lock()
        seqGen += 1
        var stamped = event
        stamped["seq"] = NSNumber(value: seqGen)
        if terminal {
            unacked.append(stamped)
            while unacked.count > UploadEventBus.maxBuffered {
                unacked.removeFirst()
            }
            persistLocked()
        }
        if let sink = sink {
            sink(stamped)
        }
        lock.unlock()
    }

    /// EventChannel onListen：接管 sink 并重放缓存的终态事件。
    func attach(_ sink: @escaping ([String: Any]) -> Void) {
        lock.lock()
        self.sink = sink
        for event in unacked {
            sink(event)
        }
        lock.unlock()
    }

    /// EventChannel onCancel。
    func detach() {
        lock.lock()
        sink = nil
        lock.unlock()
    }

    /// Dart ack：丢弃 seq ≤ 给定值的缓存终态。
    func ack(seq: Int) {
        lock.lock()
        unacked.removeAll { (($0["seq"] as? NSNumber)?.intValue ?? 0) <= seq }
        persistLocked()
        lock.unlock()
    }

    /// 任务重新注册/取消：其缓存终态作废。
    func purgeTask(taskId: String) {
        lock.lock()
        unacked.removeAll { $0["taskId"] as? String == taskId }
        persistLocked()
        lock.unlock()
    }

    // ── 终态落盘 / 恢复（进程死亡重放语义） ──────────────────────────

    /// plist 不支持 null 值——持久化前剔除 NSNull（Dart 侧以缺失等同 null）。
    private func persistLocked() {
        let storable = unacked.map { event -> [String: Any] in
            var out: [String: Any] = [:]
            for (key, value) in event {
                if let number = value as? NSNumber {
                    out[key] = number
                } else if let string = value as? String {
                    out[key] = string
                }
                // NSNull（null 值）跳过。
            }
            return out
        }
        let raw: [String: Any] = ["seq": NSNumber(value: seqGen), "unacked": storable]
        (raw as NSDictionary).write(to: fileURL, atomically: true)
    }

    private func loadPersisted() {
        guard let raw = NSDictionary(contentsOf: fileURL) as? [String: Any] else {
            return
        }
        seqGen = (raw["seq"] as? NSNumber)?.intValue ?? 0
        unacked = raw["unacked"] as? [[String: Any]] ?? []
    }
}