using Grpc.Core;
using SHH.Contracts;
using SHH.Contracts.Grpc;

namespace SHH.MjpegPlayer
{
    /// <summary>
    /// gRpc 网关服务
    /// 职责：作为服务端通讯入口，负责接收客户端（分析节点）的所有 gRpc 请求，将其转译为内部业务载荷，
    /// 并通过消息总线 MessageBus 分发至对应的业务处理器。
    /// </summary>
    public class GatewayService : GatewayProvider.GatewayProviderBase
    {
        #region 1. 逻辑身份注册 (Unary 调用)

        /// <summary>
        /// 处理分析节点的注册请求
        /// </summary>
        /// <param name="request">包含节点实例 ID 和服务器 IP 的请求对象</param>
        /// <param name="context">gRpc 调用上下文</param>
        /// <returns>操作成功响应</returns>
        public override Task<GenericResponse> RegisterInstance(RegisterRequest request, ServerCallContext context)
        {
            // 1. 将 Protobuf 契约对象转换为业务层的 RegisterPayload (DTO)
            // 职责：将外部传输格式映射为内部业务模型，实现协议与业务逻辑的解耦
            var payload = new RegisterPayload
            {
                // 身份标识映射
                ProcessId = request.ProcessId,
                InvokeProcId = request.InvokeProcessId,
                InstanceId = request.InstanceId,
                Version = request.Version,

                // 网络诊断信息映射
                ServerIp = request.ServerIp,
                WebApiPort = request.WebapiPort,
                GrpcPort = request.GrpcPort,

                // 运行时状态映射
                // 注意：将 int64 类型的 Ticks 转换为 C# 的 DateTime 对象
                StartTime = new DateTime(request.StartTimeTicks),
                Description = request.Description
            };

            // 2. 将注册载荷抛给总线，触发如 DeviceConfigHandler 的配置初始化逻辑
            // 职责：通过中介者模式分发事件，网关层不需要知道谁在处理这些数据
            MessageBus.Instance.RaiseServerRegistered(payload);

            return Task.FromResult(new GenericResponse { Success = true });
        }

        #endregion

        #region 2. 指令下发长连接 (Server Streaming)

        /// <summary>
        /// 建立并维持一个从服务器向客户端单向推送指令的长连接通道
        /// </summary>
        /// <param name="request">连接请求（包含 InstanceId）</param>
        /// <param name="responseStream">响应流，用于后续异步推送指令</param>
        /// <param name="context">gRpc 调用上下文</param>
        /// <returns>异步任务</returns>
        public override async Task OpenCommandChannel(CommandStreamRequest request, IServerStreamWriter<CommandPayloadProto> responseStream, ServerCallContext context)
        {
            // 1. 物理流登记：将此响应流句柄存入 GrpcSessionManager，以便 MessageBus 随时调用
            GrpcSessionManager.Instance.RegisterSession(request.InstanceId, responseStream);

            try
            {
                // 2. 挂起连接：利用 Task.Delay(-1) 配合取消令牌无限期挂起连接，直到客户端断开
                await Task.Delay(-1, context.CancellationToken);
            }
            catch (OperationCanceledException)
            {
                // 客户端主动取消连接属于正常预期，无需抛出异常
            }
            finally
            {
                // 3. 物理流清理：当连接断开时，必须从会话管理器中移除，防止下发指令时产生死连接
                GrpcSessionManager.Instance.RemoveSession(request.InstanceId);
            }
        }

        #endregion

        #region 3. 设备状态批量上报 (Unary 调用)

        /// <summary>
        /// 接收来自分析节点的相机在线/离线状态批量上报
        /// </summary>
        /// <param name="request">包含多个设备状态项的请求对象</param>
        /// <param name="context">gRpc 调用上下文</param>
        /// <returns>操作成功响应</returns>
        public override Task<GenericResponse> ReportStatusBatch(StatusBatchRequest request, ServerCallContext context)
        {
            if (request.Items == null || !request.Items.Any())
                return Task.FromResult(new GenericResponse { Success = true });

            // 1. 数据映射：将 Proto 集合转换为业务层的 StatusEventPayload 列表
            var payloads = request.Items.Select(item => new StatusEventPayload
            {
                CameraId = item.CameraId,
                IsOnline = item.IsOnline,
                Reason = item.Reason,
                Timestamp = request.Timestamp
            }).ToList();

            // 2. 路由分发：通过总线发布状态主题，驱动 DeviceStatusHandler 执行同步
            MessageBus.Instance.RaiseDeviceStatusReport(payloads);

            return Task.FromResult(new GenericResponse { Success = true });
        }

        #endregion

        #region 4. 视频流传输接收 (Client Streaming)

        /// <summary>
        /// 接收分析节点持续推送的视频帧数据流
        /// </summary>
        /// <param name="requestStream">客户端异步流读取器</param>
        /// <param name="context">gRpc 调用上下文</param>
        /// <returns>流关闭后的最终响应</returns>
        public override async Task<GenericResponse> UploadVideoStream(IAsyncStreamReader<VideoFrameRequest> requestStream, ServerCallContext context)
        {
            // 1. 持续读取客户端推送的每一帧数据，直到流关闭或被取消
            while (await requestStream.MoveNext(context.CancellationToken))
            {
                var frame = requestStream.Current;

                // 2. 将 Protobuf 帧数据转换为业务视频载荷 VideoPayload
                // 注意：ByteString 需要显式调用 ToByteArray 转换
                var videoPayload = new VideoPayload
                {
                    CameraId = frame.CameraId,
                    CaptureTimestamp = frame.CaptureTimestamp,
                    OriginalWidth = frame.OriginalWidth,
                    OriginalHeight = frame.OriginalHeight,
                    OriginalImageBytes = frame.OriginalImageBytes.ToByteArray(),
                    TargetImageBytes = frame.TargetImageBytes.ToByteArray(),
                    TargetWidth = frame.TargetWidth,
                    TargetHeight = frame.TargetHeight,
                    SubscriberIds = frame.SubscriberIds.ToList(),
                    HasOriginalImage = true
                };

                // 3. 导流：将图像数据直接投递给图像分发控制器进行 UI 渲染或二次处理
                ImageMonitorController.Instance.ReceivePayload(videoPayload);
            }

            return new GenericResponse { Success = true, Message = "Video stream ended" };
        }

        #endregion
    }
}