using System;
using System.IO;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Media.Imaging;

namespace ivf_tl_Operate.Debug
{
    /// <summary>
    /// operate 端 MJPEG 预览客户端:流式读 control /debug/preview/stream → 切帧 → 解码 BitmapImage → 事件回调。
    /// 断开/异常 → Stopped 事件(View 据此提示操作人员手动重开,不自动重连,spec §7)。
    /// 实例一次性:Stop/Dispose 后不可复用,需重新 new。View 每次开预览应 new 新实例。
    /// </summary>
    public sealed class MjpegStreamClient : IDisposable
    {
        private readonly string _baseUrl;   // 如 http://127.0.0.1:38080
        private HttpClient _http;
        private CancellationTokenSource _cts;
        private bool _disposed;

        /// <summary>收到一帧(已 Freeze,可跨线程贴 UI)。</summary>
        public event Action<BitmapImage> FrameReceived;
        /// <summary>预览停止(reason:断开原因,供 View 提示)。</summary>
        public event Action<string> Stopped;

        public bool IsRunning { get; private set; }

        public MjpegStreamClient(string baseUrl) { _baseUrl = baseUrl.TrimEnd('/'); }

        /// <summary>开始预览。sessionId = 第一阶段 acquire 返回的会话 id。</summary>
        public void Start(string sessionId)
        {
            if (_disposed) return;
            if (IsRunning) return;
            IsRunning = true;
            _cts = new CancellationTokenSource();
            _http = new HttpClient { Timeout = Timeout.InfiniteTimeSpan };  // 长连接,不超时掐断
            string url = $"{_baseUrl}/debug/preview/stream?sessionId={sessionId}";
            _ = Task.Run(() => ReadLoop(url, _cts.Token));
        }

        private async Task ReadLoop(string url, CancellationToken token)
        {
            string reason = "预览已结束";
            try
            {
                using (var resp = await _http.GetAsync(url, HttpCompletionOption.ResponseHeadersRead, token))
                {
                    if (!resp.IsSuccessStatusCode)
                    {
                        reason = resp.StatusCode == System.Net.HttpStatusCode.NotFound
                            ? "调试会话已超时,请重新进入调试"
                            : $"预览打开失败({(int)resp.StatusCode})";
                        return;
                    }
                    var parser = new MjpegFrameParser();
                    using (var stream = await resp.Content.ReadAsStreamAsync())
                    {
                        var buf = new byte[64 * 1024];
                        while (!token.IsCancellationRequested)
                        {
                            int n = await stream.ReadAsync(buf, 0, buf.Length, token);
                            if (n <= 0) { reason = "预览连接已断开,请重新打开预览"; break; }
                            foreach (var jpeg in parser.Feed(buf, n))
                            {
                                var img = Decode(jpeg);
                                if (img != null) FrameReceived?.Invoke(img);
                            }
                        }
                    }
                }
            }
            catch (OperationCanceledException) { reason = "预览已关闭"; }    // 主动 Stop
            catch (Exception ex)
            {
                reason = token.IsCancellationRequested
                    ? "预览已关闭"                                   // 主动 Stop 期间抛的任何异常都归为"已关闭"
                    : $"预览中断,请重新打开预览({ex.Message})";
            }
            finally
            {
                IsRunning = false;
                try { _http?.Dispose(); } catch { }   // 谁起的谁清:HttpClient 在 ReadLoop 结束时释放
                Stopped?.Invoke(reason);
            }
        }

        private static BitmapImage Decode(byte[] jpeg)
        {
            try
            {
                var img = new BitmapImage();
                using (var ms = new MemoryStream(jpeg))
                {
                    img.BeginInit();
                    img.CacheOption = BitmapCacheOption.OnLoad;   // 解完即脱离流
                    img.StreamSource = ms;
                    img.EndInit();
                }
                img.Freeze();   // 跨线程贴 UI 必须 Freeze
                return img;
            }
            catch { return null; }   // 坏帧丢弃,不打断流
        }

        /// <summary>主动停止预览(关预览按钮/返回)。token 取消是唯一停止信号,_http 由 ReadLoop finally 清理。</summary>
        public void Stop()
        {
            try { _cts?.Cancel(); } catch { }
            IsRunning = false;
        }

        public void Dispose()
        {
            _disposed = true;
            Stop();
        }
    }
}