using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using FATrace.Com;
using FATrace.Model;
using FATrace.HKNetLib.Wrapper;
using NLog;
using FATrace.OEMApp;
using TaskStatus = FATrace.Model.TaskStatus;

namespace FATrace.OEMApp.Services
{
    /// <summary>
    /// 下载任务队列（单例）。
    /// 负责：
    /// 1. 将按钮入队的下载请求持久化为 DownloadTask（Pending）
    /// 2. 后台循环按顺序逐条下载（同一时刻仅一个下载 Running）
    /// 3. 根据海康 SDK 进度事件回写 DownloadTask.Progress，便于 UI/调试观察
    /// 4. 下载完成后创建 OEMRawUse 与 JellyfinMonitorTask，为后续 Jellyfin 监听做准备
    /// 5. 异常失败时写入错误并标记 Failed，循环不中断
    /// </summary>
    public sealed class DownloadTaskWorker
    {
        private static readonly Lazy<DownloadTaskWorker> _lazy = new(() => new DownloadTaskWorker());
        public static DownloadTaskWorker Instance => _lazy.Value;

        private readonly Logger _logger = LogManager.GetCurrentClassLogger();
        private readonly SemaphoreSlim _singleRunner = new(1, 1); // 保证同一时间只有一个下载
        private CancellationTokenSource? _cts;
        private Task? _loopTask;

        private HkCamera? _hk;

        private DownloadTaskWorker() { }

        /// <summary>
        /// 启动下载队列后台循环。
        /// </summary>
        /// <param name="hk">已初始化的 HkCamera 客户端，用于发起下载与接收事件。</param>
        /// <remarks>
        /// - 该方法幂等，重复调用不会重复启动。
        /// - 启动时会将上次异常退出时处于 Running 的任务重置为 Pending，避免任务丢失。
        /// </remarks>
        public void Start(HkCamera hk)
        {
            _hk = hk ?? throw new ArgumentNullException(nameof(hk));
            if (_cts != null) return; // 已启动
            // 恢复上次未完成的运行中任务为待处理
            try
            {
                var db = FSqlContext.FDb;
                db.Update<DownloadTask>()
                  .Set(a => a.Status, TaskStatus.Pending)
                  .Set(a => a.Progress, 0)
                  .Set(a => a.UpdateTime, DateTime.Now)
                  .Where(a => a.Status == TaskStatus.Running)
                  .ExecuteAffrows();

                // 将失败的任务按最大重试次数重置为 Pending，程序重启后可自动再次尝试
                // 最大重试次数从配置读取（appSettings: DownloadTaskMaxRetry，默认 3）
                var maxRetry = ConfigHelper.GetIntOrDefault("DownloadTaskMaxRetry", 3);
                db.Update<DownloadTask>()
                  .Set(a => a.Status, TaskStatus.Pending)
                  .Set(a => a.Error, "")
                  .Set(a => a.Progress, 0)
                  .Set(a => a.UpdateTime, DateTime.Now)
                  .Where(a => a.Status == TaskStatus.Failed && a.TryCount < maxRetry)
                  .ExecuteAffrows();

            }
            catch { }
            _cts = new CancellationTokenSource();
            _loopTask = Task.Run(() => RunAsync(_cts.Token));
            _logger.Info("[DownloadTaskWorker] 已启动");
        }

        /// <summary>
        /// 停止下载队列后台循环（尽力而为）。
        /// </summary>
        public void Stop()
        {
            try
            {
                _cts?.Cancel();
            }
            catch { }
            finally
            {
                _cts = null;
            }
        }

        /// <summary>
        /// 入队一个下载任务（同时持久化到数据库）。
        /// </summary>
        /// <param name="code">业务条码/编号，关联 OEMRawUse.Code 与 VideoAction.Code。</param>
        /// <param name="rawName">原料名称。</param>
        /// <param name="user">操作用户。</param>
        /// <param name="start">NVR 下载开始时间（默认当前时间-5 分钟）。</param>
        /// <param name="end">NVR 下载结束时间（默认当前时间）。</param>
        /// <returns>新增 DownloadTask 的自增 Id。</returns>
        public long Enqueue(string code, string rawName, string user, DateTime? start = null, DateTime? end = null)
        {
            if (string.IsNullOrWhiteSpace(code)) throw new ArgumentException("code 不能为空");
            if (string.IsNullOrWhiteSpace(rawName)) throw new ArgumentException("rawName 不能为空");
            if (string.IsNullOrWhiteSpace(user)) throw new ArgumentException("user 不能为空");

            var now = DateTime.Now;
            var task = new DownloadTask
            {
                Code = code,
                RawName = rawName,
                User = user,
                Status = TaskStatus.Pending,
                Progress = 0,
                NvrStartTime = start ?? now.AddMinutes(-5),
                NvrEndTime = end ?? now,
                CreateTime = now,
                UpdateTime = now
            };

            var id = FSqlContext.FDb.Insert<DownloadTask>(task).ExecuteIdentity();
            _logger.Info("[DownloadTaskWorker] 入队 DownloadTask: Id={Id}, Code={Code}", id, code);
            return id;
        }

        /// <summary>
        /// 后台主循环：定期拉取最早的 Pending 任务并顺序处理
        /// </summary>
        /// <param name="token">取消令牌</param>
        private async Task RunAsync(CancellationToken token)
        {
            while (!token.IsCancellationRequested)
            {
                try
                {
                    // 查询最早入队但未处理的任务
                    var db = FSqlContext.FDb;
                    var next = await db.Select<DownloadTask>()
                        .Where(t => t.Status == TaskStatus.Pending)
                        .OrderBy(t => t.Id)
                        .FirstAsync();

                    if (next == null)
                    {
                        // 暂无任务，稍候再查
                        await Task.Delay(1000, token);
                        continue;
                    }

                    // 使用信号量确保同一时间仅有一个任务进入下载处理
                    await _singleRunner.WaitAsync(token);
                    _ = ProcessTaskAsync(next, token).ContinueWith(_ => _singleRunner.Release());
                }
                catch (OperationCanceledException)
                {
                    break;
                }
                catch (Exception ex)
                {
                    _logger.Error(ex, "[DownloadTaskWorker] 主循环异常");
                    try { await Task.Delay(2000, token); } catch { }
                }
            }
            _logger.Info("[DownloadTaskWorker] 已停止");
        }

        /// <summary>
        /// 实际执行单个下载任务：
        /// 1) 标记 Running，生成保存路径
        /// 2) 订阅 SDK 事件以回写进度
        /// 3) 发起下载并等待完成
        /// 4) 下载成功 -> 写 OEMRawUse 与 JellyfinMonitorTask
        /// </summary>
        /// <param name="t">待处理的 DownloadTask。</param>
        /// <param name="token">取消令牌。</param>
        private async Task ProcessTaskAsync(DownloadTask t, CancellationToken token)
        {
            if (_hk == null)
            {
                _logger.Warn("[DownloadTaskWorker] HkCamera 未初始化，跳过任务 Id={Id}", t.Id);
                return;
            }

            var db = FSqlContext.FDb;

            // 标记运行中
            t.Status = TaskStatus.Running;
            t.TryCount += 1;
            t.Progress = 0;
            t.UpdateTime = DateTime.Now;
            await db.Update<DownloadTask>()
                .SetSource(t)
                .UpdateColumns(a => new { a.Status, a.TryCount, a.Progress, a.UpdateTime })
                .Where(a => a.Id == t.Id)
                .ExecuteAffrowsAsync();

            // 生成本地文件名/路径
            var saveBase = _hk.NVRVideoSavePath;
            if (string.IsNullOrWhiteSpace(saveBase))
            {
                _logger.Error("[DownloadTaskWorker] NVRVideoSavePath 为空，无法下载。任务 Id={Id}", t.Id);
                await MarkFailedAsync(t, "NVRVideoSavePath 未配置");
                return;
            }
            var filePath = NVRCom.GetVideoName(saveBase, t.Code ?? "CODE");
            await db.Update<DownloadTask>()
                .Set(a => a.VideoFilePath, filePath)
                .Set(a => a.UpdateTime, DateTime.Now)
                .Where(a => a.Id == t.Id)
                .ExecuteAffrowsAsync();

            // 事件 -> TCS
            // 订阅两个事件：进度与完成。进度事件写回数据库；完成事件用于唤醒等待
            var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
            
            void OnProgress(object? s, short p)
            {
                try
                {
                    db.Update<DownloadTask>()
                      .Set(a => a.Progress, Math.Max((short)0, Math.Min((short)100, p)))
                      .Set(a => a.UpdateTime, DateTime.Now)
                      .Where(a => a.Id == t.Id)
                      .ExecuteAffrows();
                }
                catch { }
            }
            void OnComplete(object? s, string msg)
            {
                try
                {
                    tcs.TrySetResult(true);
                }
                catch { }
            }

            _hk.NVRLoadVideoProcessEventHandler += OnProgress;
            _hk.NVRLoadVideoCompleteEventHandler += OnComplete;

            try
            {
                // 发起下载（按时间范围）
                var res = _hk.Sdk_NET_DVR_GetFileByTime_V40(t.NvrStartTime, t.NvrEndTime, filePath);
                if (!res.Result)
                {
                    await MarkFailedAsync(t, res.Msg);
                    return;
                }

                // HkCamera 内部会启动进度监控：此处等待完成事件触发
                using (token.Register(() => tcs.TrySetCanceled()))
                {
                    await tcs.Task;
                }

                // 下载完成：写 OEMRawUse 并创建 JellyfinMonitorTask
                // 1) 插入 OEMRawUse（UrlState=false, VideoUrl 空）
                var rawUse = new OEMRawUse
                {
                    InBagCode = t.Code,
                    RawName = t.RawName,
                    User = t.User,
                    UrlState = false,
                    VideoUrl = string.Empty,
                    CreateTime = DateTime.Now,
                    VideoActionId = 0
                };
                var rawUseId = db.Insert<OEMRawUse>(rawUse).ExecuteIdentity();

                // 2) 创建 Jellyfin 监听任务，交由 JellyfinMonitorQueueService 批量匹配
                var jfTask = new JellyfinMonitorTask
                {
                    OemRawUseId = rawUseId,
                    LocalFileNameOrPath = filePath,
                    Code = t.Code,
                    RawName = t.RawName,
                    User = t.User,
                    NvrStartTime = t.NvrStartTime,
                    NvrEndTime = t.NvrEndTime,
                    Status = TaskStatus.Pending,
                    TryCount = 0,
                    CreateTime = DateTime.Now,
                    UpdateTime = DateTime.Now
                };
                db.Insert<JellyfinMonitorTask>(jfTask).ExecuteAffrows();

                // 标记下载完成
                t.Status = TaskStatus.Completed;
                t.Progress = 100;
                t.UpdateTime = DateTime.Now;
                await db.Update<DownloadTask>()
                    .SetSource(t)
                    .UpdateColumns(a => new { a.Status, a.Progress, a.UpdateTime })
                    .Where(a => a.Id == t.Id)
                    .ExecuteAffrowsAsync();

                _logger.Info("[DownloadTaskWorker] 下载完成，已创建 Jellyfin 监控任务。DownloadTaskId={Id}, OEMRawUseId={RawUseId}", t.Id, rawUseId);
            }
            catch (OperationCanceledException)
            {
                await MarkFailedAsync(t, "任务被取消");
            }
            catch (Exception ex)
            {
                await MarkFailedAsync(t, ex.Message);
            }
            finally
            {
                // 释放事件订阅，避免内存泄露或重复触发
                try { _hk.NVRLoadVideoProcessEventHandler -= OnProgress; } catch { }
                try { _hk.NVRLoadVideoCompleteEventHandler -= OnComplete; } catch { }
            }
        }

        /// <summary>
        /// 将任务标记为失败，并持久化错误信息。
        /// </summary>
        /// <param name="t">下载任务。</param>
        /// <param name="error">错误描述（可空）。</param>
        private Task MarkFailedAsync(DownloadTask t, string? error)
        {
            var db = FSqlContext.FDb;
            t.Status = TaskStatus.Failed;
            t.Error = error;
            t.UpdateTime = DateTime.Now;
            _logger.Warn("[DownloadTaskWorker] 任务失败 Id={Id}, 错误={Err}", t.Id, error);
            return db.Update<DownloadTask>()
                .SetSource(t)
                .UpdateColumns(a => new { a.Status, a.Error, a.UpdateTime })
                .Where(a => a.Id == t.Id)
                .ExecuteAffrowsAsync();
        }
    }
}