using System.Collections.Concurrent;
using Google.Protobuf.WellKnownTypes;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.MxGateway.Contracts;
using ZB.MOM.WW.MxGateway.Contracts.Proto;
using ZB.MOM.WW.MxGateway.Server.Configuration;
using ZB.MOM.WW.MxGateway.Server.Grpc;
using ZB.MOM.WW.MxGateway.Server.Metrics;
using ZB.MOM.WW.MxGateway.Server.Security.Authentication;
using ZB.MOM.WW.MxGateway.Server.Security.Authorization;
using ZB.MOM.WW.MxGateway.Server.Sessions;
using ZB.MOM.WW.MxGateway.Server.Workers;
using ZB.MOM.WW.MxGateway.Tests.Gateway.Workers.Fakes;
using ZB.MOM.WW.MxGateway.Tests.TestSupport;

namespace ZB.MOM.WW.MxGateway.Tests.Gateway;

public sealed class GatewayEndToEndFakeWorkerSmokeTests
{
    private static readonly TimeSpan TestTimeout = TimeSpan.FromSeconds(5);
    private const int ServerHandle = 1001;
    private const int ItemHandle = 2002;

    /// <summary>
    /// Verifies gateway session lifecycle with a scripted fake worker: open, command, event, close.
    /// </summary>
    [Fact]
    public async Task GatewayService_WithFakeWorker_CompletesSessionCommandEventAndClosePath()
    {
        ScriptedFakeWorkerProcessLauncher launcher = new();
        await using GatewayServiceFixture fixture = new(launcher);

        OpenSessionReply openReply = await fixture.Service.OpenSession(
            new OpenSessionRequest
            {
                ClientSessionName = "fake-worker-e2e",
                ClientCorrelationId = "open-correlation",
                CommandTimeout = Duration.FromTimeSpan(TestTimeout),
            },
            new TestServerCallContext());

        RecordingServerStreamWriter<MxEvent> eventWriter = new();
        Task streamTask = fixture.Service.StreamEvents(
            new StreamEventsRequest { SessionId = openReply.SessionId },
            eventWriter,
            new TestServerCallContext());

        MxCommandReply registerReply = await fixture.Service.Invoke(
            CreateRegisterRequest(openReply.SessionId),
            new TestServerCallContext());
        MxCommandReply addItemReply = await fixture.Service.Invoke(
            CreateAddItemRequest(openReply.SessionId, registerReply.Register.ServerHandle),
            new TestServerCallContext());
        MxCommandReply adviseReply = await fixture.Service.Invoke(
            CreateAdviseRequest(openReply.SessionId, registerReply.Register.ServerHandle, addItemReply.AddItem.ItemHandle),
            new TestServerCallContext());

        MxEvent dataChange = await eventWriter.WaitForFirstMessageAsync(TestTimeout);

        CloseSessionReply closeReply = await fixture.Service.CloseSession(
            new CloseSessionRequest
            {
                SessionId = openReply.SessionId,
                ClientCorrelationId = "close-correlation",
            },
            new TestServerCallContext());

        await streamTask.WaitAsync(TestTimeout);
        await launcher.WorkerTask.WaitAsync(TestTimeout);

        Assert.Equal(ProtocolStatusCode.Ok, openReply.ProtocolStatus.Code);
        Assert.Equal(GatewayContractInfo.DefaultBackendName, openReply.BackendName);
        Assert.Equal(ScriptedFakeWorkerProcessLauncher.ProcessId, openReply.WorkerProcessId);
        Assert.Equal(ProtocolStatusCode.Ok, registerReply.ProtocolStatus.Code);
        Assert.Equal(ServerHandle, registerReply.Register.ServerHandle);
        Assert.Equal(ProtocolStatusCode.Ok, addItemReply.ProtocolStatus.Code);
        Assert.Equal(ItemHandle, addItemReply.AddItem.ItemHandle);
        Assert.Equal(ProtocolStatusCode.Ok, adviseReply.ProtocolStatus.Code);
        Assert.Equal(MxEventFamily.OnDataChange, dataChange.Family);
        Assert.Equal(openReply.SessionId, dataChange.SessionId);
        Assert.Equal(ServerHandle, dataChange.ServerHandle);
        Assert.Equal(ItemHandle, dataChange.ItemHandle);
        Assert.Equal("scripted-value", dataChange.Value.StringValue);
        Assert.Equal(ProtocolStatusCode.Ok, closeReply.ProtocolStatus.Code);
        Assert.Equal(SessionState.Closed, closeReply.FinalState);
        Assert.True(launcher.Process.HasExited);
        // MarkExited(0) is reached only after the scripted worker observed a WorkerShutdown
        // envelope and emitted its WorkerShutdownAck — anything else (a kill, a fault) would
        // have produced a non-zero exit code, so this pins the shutdown-ack handshake.
        Assert.Equal(0, launcher.Process.ExitCode);
        Assert.Equal(
            [MxCommandKind.Register, MxCommandKind.AddItem, MxCommandKind.Advise],
            launcher.CommandKinds);
    }

    private static MxCommandRequest CreateRegisterRequest(string sessionId)
    {
        return new MxCommandRequest
        {
            SessionId = sessionId,
            ClientCorrelationId = "register-correlation",
            Command = new MxCommand
            {
                Kind = MxCommandKind.Register,
                Register = new RegisterCommand { ClientName = "fake-worker-e2e-client" },
            },
        };
    }

    private static MxCommandRequest CreateAddItemRequest(
        string sessionId,
        int serverHandle)
    {
        return new MxCommandRequest
        {
            SessionId = sessionId,
            ClientCorrelationId = "add-item-correlation",
            Command = new MxCommand
            {
                Kind = MxCommandKind.AddItem,
                AddItem = new AddItemCommand
                {
                    ServerHandle = serverHandle,
                    ItemDefinition = "Galaxy.Tag.Value",
                },
            },
        };
    }

    private static MxCommandRequest CreateAdviseRequest(
        string sessionId,
        int serverHandle,
        int itemHandle)
    {
        return new MxCommandRequest
        {
            SessionId = sessionId,
            ClientCorrelationId = "advise-correlation",
            Command = new MxCommand
            {
                Kind = MxCommandKind.Advise,
                Advise = new AdviseCommand
                {
                    ServerHandle = serverHandle,
                    ItemHandle = itemHandle,
                },
            },
        };
    }

    private sealed class GatewayServiceFixture : IAsyncDisposable
    {
        private readonly GatewayMetrics _metrics = new();
        private readonly SessionRegistry _registry = new();

        /// <summary>
        /// Initializes a new instance of <see cref="GatewayServiceFixture"/>.
        /// </summary>
        /// <param name="launcher">Worker process launcher for the fixture.</param>
        public GatewayServiceFixture(IWorkerProcessLauncher launcher)
        {
            IOptions<GatewayOptions> options = Options.Create(CreateOptions());
            SessionWorkerClientFactory workerClientFactory = new(
                launcher,
                options,
                _metrics,
                NullLoggerFactory.Instance);
            SessionManager sessionManager = new(
                _registry,
                workerClientFactory,
                options,
                _metrics,
                logger: NullLogger<SessionManager>.Instance);
            MxAccessGrpcMapper mapper = new();
            EventStreamService eventStreamService = new(
                sessionManager,
                options,
                mapper,
                _metrics,
                NullDashboardEventBroadcaster.Instance,
                NullLogger<EventStreamService>.Instance);

            Service = new MxAccessGatewayService(
                sessionManager,
                new GatewayRequestIdentityAccessor(),
                new AllowAllConstraintEnforcer(),
                new MxAccessGrpcRequestValidator(),
                mapper,
                eventStreamService,
                _metrics,
                NullLogger<MxAccessGatewayService>.Instance,
                new FakeGatewayAlarmService());
        }

        /// <summary>
        /// Gets the configured gateway service instance.
        /// </summary>
        public MxAccessGatewayService Service { get; }

        /// <summary>
        /// Disposes all active sessions and metrics.
        /// </summary>
        public async ValueTask DisposeAsync()
        {
            foreach (GatewaySession session in _registry.Snapshot())
            {
                await session.DisposeAsync();
            }

            _metrics.Dispose();
        }

        private static GatewayOptions CreateOptions()
        {
            return new GatewayOptions
            {
                Worker = new WorkerOptions
                {
                    StartupTimeoutSeconds = 5,
                    ShutdownTimeoutSeconds = 5,
                    HeartbeatIntervalSeconds = 30,
                    HeartbeatGraceSeconds = 30,
                    MaxMessageBytes = WorkerFrameProtocolOptions.DefaultMaxMessageBytes,
                },
                Sessions = new SessionOptions
                {
                    DefaultCommandTimeoutSeconds = 5,
                    MaxSessions = 4,
                },
                Events = new EventOptions
                {
                    QueueCapacity = 16,
                },
            };
        }
    }

    private sealed class ScriptedFakeWorkerProcessLauncher : IWorkerProcessLauncher
    {
        public const int ProcessId = 4680;
        private readonly ConcurrentQueue<MxCommandKind> _commandKinds = new();

        /// <summary>
        /// Gets the fake worker process instance.
        /// </summary>
        public FakeWorkerProcess Process { get; } = new(ProcessId);

        /// <summary>
        /// Gets the collection of command kinds processed by the worker.
        /// </summary>
        public IReadOnlyCollection<MxCommandKind> CommandKinds => _commandKinds.ToArray();

        /// <summary>
        /// Gets the worker's asynchronous task.
        /// </summary>
        public Task WorkerTask { get; private set; } = Task.CompletedTask;

        /// <summary>
        /// Launches a new worker process and returns a handle to manage it.
        /// </summary>
        /// <param name="request">Worker process launch request parameters.</param>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>Worker process handle.</returns>
        public Task<WorkerProcessHandle> LaunchAsync(
            WorkerProcessLaunchRequest request,
            CancellationToken cancellationToken = default)
        {
            WorkerTask = RunWorkerAsync(request, cancellationToken);

            return Task.FromResult(new WorkerProcessHandle(
                Process,
                new WorkerProcessCommandLine("fake-worker.exe", []),
                DateTimeOffset.UtcNow));
        }

        private async Task RunWorkerAsync(
            WorkerProcessLaunchRequest request,
            CancellationToken cancellationToken)
        {
            await using FakeWorkerHarness harness = await FakeWorkerHarness.ConnectToGatewayPipeAsync(
                request.SessionId,
                request.Nonce,
                request.PipeName,
                request.ProtocolVersion,
                cancellationToken: cancellationToken).ConfigureAwait(false);
            await harness.CompleteStartupAsync(ProcessId, cancellationToken: cancellationToken).ConfigureAwait(false);

            while (!cancellationToken.IsCancellationRequested)
            {
                WorkerEnvelope envelope = await harness.ReadGatewayEnvelopeAsync(cancellationToken).ConfigureAwait(false);
                if (envelope.BodyCase == WorkerEnvelope.BodyOneofCase.WorkerCommand)
                {
                    await ReplyToCommandAsync(harness, envelope, cancellationToken).ConfigureAwait(false);
                    continue;
                }

                if (envelope.BodyCase == WorkerEnvelope.BodyOneofCase.WorkerShutdown)
                {
                    await harness.SendShutdownAckAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
                    Process.MarkExited(0);
                    return;
                }

                throw new InvalidOperationException($"Unexpected gateway envelope {envelope.BodyCase}.");
            }
        }

        private async Task ReplyToCommandAsync(
            FakeWorkerHarness harness,
            WorkerEnvelope commandEnvelope,
            CancellationToken cancellationToken)
        {
            MxCommand command = commandEnvelope.WorkerCommand.Command;
            _commandKinds.Enqueue(command.Kind);

            await harness.ReplyToCommandAsync(
                commandEnvelope,
                configureReply: reply => ConfigureReply(reply, command.Kind),
                cancellationToken: cancellationToken).ConfigureAwait(false);

            if (command.Kind == MxCommandKind.Advise)
            {
                await harness.EmitEventAsync(
                    MxEventFamily.OnDataChange,
                    cancellationToken,
                    mxEvent =>
                    {
                        mxEvent.ServerHandle = command.Advise.ServerHandle;
                        mxEvent.ItemHandle = command.Advise.ItemHandle;
                        mxEvent.Quality = 192;
                        mxEvent.Value = new MxValue
                        {
                            DataType = MxDataType.String,
                            StringValue = "scripted-value",
                        };
                        mxEvent.OnDataChange = new OnDataChangeEvent();
                    }).ConfigureAwait(false);
            }
        }

        private static void ConfigureReply(
            MxCommandReply reply,
            MxCommandKind kind)
        {
            switch (kind)
            {
                case MxCommandKind.Register:
                    reply.Register = new RegisterReply { ServerHandle = ServerHandle };
                    break;
                case MxCommandKind.AddItem:
                    reply.AddItem = new AddItemReply { ItemHandle = ItemHandle };
                    break;
            }
        }
    }

    private sealed class FakeWorkerProcess(int processId) : IWorkerProcess
    {
        private readonly TaskCompletionSource _exited = new(TaskCreationOptions.RunContinuationsAsynchronously);

        /// <summary>
        /// Gets the process identifier.
        /// </summary>
        public int Id { get; } = processId;

        /// <summary>
        /// Gets a value indicating whether the process has exited.
        /// </summary>
        public bool HasExited { get; private set; }

        /// <summary>
        /// Gets the exit code of the process.
        /// </summary>
        public int? ExitCode { get; private set; }

        /// <summary>
        /// Waits for the process to exit asynchronously. Completes only when <see cref="Kill"/>
        /// or <see cref="MarkExited"/> has been called, so callers that observe completion can
        /// trust that exit actually happened (e.g., via the worker shutdown-ack path).
        /// </summary>
        /// <param name="cancellationToken">Cancellation token.</param>
        /// <returns>A task that completes when the process has actually exited.</returns>
        public ValueTask WaitForExitAsync(CancellationToken cancellationToken)
        {
            return new ValueTask(_exited.Task.WaitAsync(cancellationToken));
        }

        /// <summary>
        /// Terminates the process.
        /// </summary>
        /// <param name="entireProcessTree">Whether to kill the entire process tree.</param>
        public void Kill(bool entireProcessTree)
        {
            MarkExited(-1);
        }

        /// <summary>
        /// Releases resources used by this process.
        /// </summary>
        public void Dispose()
        {
        }

        /// <summary>
        /// Marks the process as exited with the specified exit code.
        /// </summary>
        /// <param name="exitCode">The process exit code.</param>
        public void MarkExited(int exitCode)
        {
            HasExited = true;
            ExitCode = exitCode;
            _exited.TrySetResult();
        }
    }

}