using Grpc.Core;
using MxGateway.Contracts;
using MxGateway.Contracts.Proto;
using MxGateway.Server.Security.Authorization;
using MxGateway.Server.Sessions;
using MxGateway.Server.Workers;

namespace MxGateway.Server.Grpc;

public sealed class MxAccessGatewayService(
    ISessionManager sessionManager,
    IGatewayRequestIdentityAccessor identityAccessor,
    MxAccessGrpcRequestValidator requestValidator,
    MxAccessGrpcMapper mapper,
    IEventStreamService eventStreamService,
    ILogger<MxAccessGatewayService> logger) : MxAccessGateway.MxAccessGatewayBase
{
    public override async Task<OpenSessionReply> OpenSession(
        OpenSessionRequest request,
        ServerCallContext context)
    {
        try
        {
            requestValidator.ValidateOpenSession(request);
            GatewaySession session = await sessionManager
                .OpenSessionAsync(
                    SessionOpenRequest.FromContract(request),
                    ResolveClientIdentity(),
                    context.CancellationToken)
                .ConfigureAwait(false);

            OpenSessionReply reply = new()
            {
                SessionId = session.SessionId,
                BackendName = session.BackendName,
                WorkerProcessId = session.WorkerProcessId ?? 0,
                WorkerProtocolVersion = GatewayContractInfo.WorkerProtocolVersion,
                DefaultCommandTimeout = Google.Protobuf.WellKnownTypes.Duration.FromTimeSpan(session.CommandTimeout),
                ProtocolStatus = MxAccessGrpcMapper.Ok(),
            };
            reply.Capabilities.Add("unary-open-session");
            reply.Capabilities.Add("unary-close-session");
            reply.Capabilities.Add("unary-invoke");
            reply.Capabilities.Add("server-stream-events");

            return reply;
        }
        catch (Exception exception) when (exception is not RpcException)
        {
            throw MapException(exception);
        }
    }

    public override async Task<CloseSessionReply> CloseSession(
        CloseSessionRequest request,
        ServerCallContext context)
    {
        try
        {
            requestValidator.ValidateCloseSession(request);
            SessionCloseResult result = await sessionManager
                .CloseSessionAsync(request.SessionId, context.CancellationToken)
                .ConfigureAwait(false);

            return new CloseSessionReply
            {
                SessionId = result.SessionId,
                FinalState = result.FinalState,
                ProtocolStatus = MxAccessGrpcMapper.Ok(result.AlreadyClosed ? "Session was already closed." : "Session closed."),
            };
        }
        catch (Exception exception) when (exception is not RpcException)
        {
            throw MapException(exception);
        }
    }

    public override async Task<MxCommandReply> Invoke(
        MxCommandRequest request,
        ServerCallContext context)
    {
        try
        {
            requestValidator.ValidateInvoke(request);
            WorkerCommand workerCommand = mapper.MapCommand(request);
            WorkerCommandReply workerReply = await sessionManager
                .InvokeAsync(request.SessionId, workerCommand, context.CancellationToken)
                .ConfigureAwait(false);

            return mapper.MapCommandReply(workerReply);
        }
        catch (Exception exception) when (exception is not RpcException)
        {
            throw MapException(exception);
        }
    }

    public override async Task StreamEvents(
        StreamEventsRequest request,
        IServerStreamWriter<MxEvent> responseStream,
        ServerCallContext context)
    {
        try
        {
            requestValidator.ValidateStreamEvents(request);
            await foreach (MxEvent publicEvent in eventStreamService
                .StreamEventsAsync(request, context.CancellationToken)
                .WithCancellation(context.CancellationToken)
                .ConfigureAwait(false))
            {
                await responseStream.WriteAsync(publicEvent).ConfigureAwait(false);
            }
        }
        catch (Exception exception) when (exception is not RpcException)
        {
            throw MapException(exception);
        }
    }

    private string? ResolveClientIdentity()
    {
        return identityAccessor.Current?.DisplayName ?? identityAccessor.Current?.KeyId;
    }

    private RpcException MapException(Exception exception)
    {
        if (exception is OperationCanceledException)
        {
            return new RpcException(new Status(StatusCode.Cancelled, "gRPC request was canceled."));
        }

        if (exception is SessionManagerException sessionException)
        {
            return MapSessionException(sessionException);
        }

        if (exception is WorkerClientException workerClientException)
        {
            return MapWorkerClientException(workerClientException);
        }

        logger.LogWarning(exception, "Public gRPC request failed.");
        return new RpcException(new Status(StatusCode.Unavailable, "Gateway request failed before an MXAccess reply was available."));
    }

    private static RpcException MapSessionException(SessionManagerException exception)
    {
        StatusCode statusCode = exception.ErrorCode switch
        {
            SessionManagerErrorCode.SessionNotFound => StatusCode.NotFound,
            SessionManagerErrorCode.SessionNotReady => StatusCode.FailedPrecondition,
            SessionManagerErrorCode.EventSubscriberAlreadyActive => StatusCode.ResourceExhausted,
            SessionManagerErrorCode.EventQueueOverflow => StatusCode.ResourceExhausted,
            SessionManagerErrorCode.SessionLimitExceeded => StatusCode.ResourceExhausted,
            SessionManagerErrorCode.OpenFailed => StatusCode.Unavailable,
            SessionManagerErrorCode.CloseFailed => StatusCode.Unavailable,
            _ => StatusCode.Unavailable,
        };

        return new RpcException(new Status(statusCode, exception.Message));
    }

    private static RpcException MapWorkerClientException(WorkerClientException exception)
    {
        StatusCode statusCode = exception.ErrorCode switch
        {
            WorkerClientErrorCode.CommandTimeout => StatusCode.DeadlineExceeded,
            WorkerClientErrorCode.GatewayShutdown => StatusCode.Cancelled,
            WorkerClientErrorCode.InvalidState => StatusCode.FailedPrecondition,
            WorkerClientErrorCode.ProtocolViolation => StatusCode.Internal,
            _ => StatusCode.Unavailable,
        };

        return new RpcException(new Status(statusCode, exception.Message));
    }
}