using System;
using System.IO;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using ChannelsNS = System.Threading.Channels;
using XWorld.Framework.Protocol;

namespace XWorld.Server.Gateway
{
    // 一个 WebSocket 连接：收循环解码帧→Submit；发循环排空出站队列→SendAsync（每 socket 仅一个发循环，发送串行）
    public sealed class Connection : IClientConnection
    {
        public int PlayerId { get; }

        private readonly WebSocket _socket;
        private readonly ServerLoop _loop;
        private readonly ChannelsNS.Channel<byte[]> _outbound = ChannelsNS.Channel.CreateUnbounded<byte[]>();

        public Connection(int playerId, WebSocket socket, ServerLoop loop)
        {
            PlayerId = playerId; _socket = socket; _loop = loop;
        }

        public void Send(byte[] frame) => _outbound.Writer.TryWrite(frame);

        public async Task RunAsync(CancellationToken ct)
        {
            var sendTask = SendLoopAsync(ct);
            try { await ReceiveLoopAsync(ct).ConfigureAwait(false); }
            finally
            {
                _outbound.Writer.TryComplete();
                await sendTask.ConfigureAwait(false);
            }
        }

        private async Task ReceiveLoopAsync(CancellationToken ct)
        {
            var buf = new byte[8192];
            using var ms = new MemoryStream();
            try
            {
                while (_socket.State == WebSocketState.Open && !ct.IsCancellationRequested)
                {
                    ms.SetLength(0);
                    WebSocketReceiveResult res;
                    do
                    {
                        res = await _socket.ReceiveAsync(new ArraySegment<byte>(buf), ct).ConfigureAwait(false);
                        if (res.MessageType == WebSocketMessageType.Close) return;
                        ms.Write(buf, 0, res.Count);
                    } while (!res.EndOfMessage);

                    Frame frame;
                    try { frame = FrameCodec.Decode(ms.ToArray()); }
                    catch (FormatException) { continue; } // 畸形帧：丢弃，不拖垮连接

                    _loop.Submit(new FrameCommand { PlayerId = PlayerId, Frame = frame });
                }
            }
            catch (OperationCanceledException) { } // 主机关停/请求中止
            catch (WebSocketException) { }          // 对端突然断开（TCP 掉线）
        }

        private async Task SendLoopAsync(CancellationToken ct)
        {
            try
            {
                await foreach (var frame in _outbound.Reader.ReadAllAsync(ct).ConfigureAwait(false))
                {
                    if (_socket.State != WebSocketState.Open) break;
                    await _socket.SendAsync(new ArraySegment<byte>(frame),
                        WebSocketMessageType.Binary, true, ct).ConfigureAwait(false);
                }
            }
            catch (OperationCanceledException) { }
            catch (WebSocketException) { } // 对端已断，停止发送
        }
    }
}