using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using MxGateway.Contracts.Proto;
using MxGateway.Worker.MxAccess;
using MxGateway.Worker.Sta;

namespace MxGateway.Worker.Tests.MxAccess;

/// <summary>
/// Tests for <see cref="MxAccessStaSession"/>.
/// </summary>
public sealed class MxAccessStaSessionTests
{
    /// <summary>
    /// Verifies that StartAsync creates the MXAccess COM object and attaches the event sink on the STA thread.
    /// </summary>
    [Fact]
    public async Task StartAsync_CreatesComObjectAndAttachesEventSinkOnStaThread()
    {
        FakeMxAccessComObjectFactory factory = new();
        FakeMxAccessEventSink eventSink = new();
        using StaRuntime runtime = CreateRuntime();
        using MxAccessStaSession session = new(runtime, factory, eventSink);

        WorkerReady ready = await session.StartAsync("session-1", workerProcessId: 1234);

        Assert.Equal(1234, ready.WorkerProcessId);
        Assert.Equal(MxAccessInteropInfo.ProgId, ready.MxaccessProgid);
        Assert.Equal(MxAccessInteropInfo.Clsid, ready.MxaccessClsid);
        Assert.NotNull(ready.ReadyTimestamp);
        Assert.Equal(runtime.StaThreadId, factory.CreateThreadId);
        Assert.Equal(runtime.StaThreadId, eventSink.AttachThreadId);
        Assert.Equal(ApartmentState.STA, factory.CreateApartmentState);
        Assert.Same(factory.CreatedObject, eventSink.AttachedObject);
        Assert.Equal("session-1", eventSink.SessionId);
    }

    /// <summary>
    /// Verifies that StartAsync maps creation exceptions with HResult when the factory fails.
    /// </summary>
    [Fact]
    public async Task StartAsync_WhenFactoryFails_MapsCreationExceptionWithHResult()
    {
        const int hresult = unchecked((int)0x80040154);
        FakeMxAccessComObjectFactory factory = new(new COMException("Class not registered.", hresult));
        FakeMxAccessEventSink eventSink = new();
        using StaRuntime runtime = CreateRuntime();
        using MxAccessStaSession session = new(runtime, factory, eventSink);

        MxAccessCreationException exception = await Assert.ThrowsAsync<MxAccessCreationException>(
            () => session.StartAsync(workerProcessId: 1234));

        Assert.Equal(hresult, exception.CapturedHResult);
        Assert.Equal(MxAccessInteropInfo.ProgId, exception.AttemptedProgId);
        Assert.Equal(MxAccessInteropInfo.Clsid, exception.AttemptedClsid);
        Assert.Null(eventSink.AttachedObject);
    }

    /// <summary>
    /// Verifies that Dispose detaches the event sink on the STA thread.
    /// </summary>
    [Fact]
    public async Task Dispose_DetachesEventSinkOnStaThread()
    {
        FakeMxAccessComObjectFactory factory = new();
        FakeMxAccessEventSink eventSink = new();
        using StaRuntime runtime = CreateRuntime();
        MxAccessStaSession session = new(runtime, factory, eventSink);
        await session.StartAsync(workerProcessId: 1234);

        session.Dispose();

        Assert.Equal(runtime.StaThreadId, eventSink.DetachThreadId);
    }

    private static StaRuntime CreateRuntime()
    {
        return new StaRuntime(
            new NoopComApartmentInitializer(),
            new StaMessagePump(),
            TimeSpan.FromMilliseconds(25));
    }

    /// <summary>
    /// Fake MXAccess COM object factory for testing.
    /// </summary>
    private sealed class FakeMxAccessComObjectFactory : IMxAccessComObjectFactory
    {
        private readonly Exception? exception;

        /// <summary>
        /// Initializes a fake factory that optionally throws an exception.
        /// </summary>
        /// <param name="exception">Exception to throw when Create is called; null to succeed.</param>
        public FakeMxAccessComObjectFactory(Exception? exception = null)
        {
            this.exception = exception;
        }

        /// <summary>
        /// Gets the COM object created by this factory.
        /// </summary>
        public object CreatedObject { get; } = new();

        /// <summary>
        /// Gets the managed thread ID when Create was called.
        /// </summary>
        public int? CreateThreadId { get; private set; }

        /// <summary>
        /// Gets the apartment state when Create was called.
        /// </summary>
        public ApartmentState? CreateApartmentState { get; private set; }

        /// <summary>
        /// Creates the COM object or throws the configured exception.
        /// </summary>
        public object Create()
        {
            CreateThreadId = Thread.CurrentThread.ManagedThreadId;
            CreateApartmentState = Thread.CurrentThread.GetApartmentState();

            if (exception is not null)
            {
                throw exception;
            }

            return CreatedObject;
        }
    }

    /// <summary>
    /// Fake MXAccess event sink for testing.
    /// </summary>
    private sealed class FakeMxAccessEventSink : IMxAccessEventSink
    {
        /// <summary>
        /// Gets the attached MXAccess COM object.
        /// </summary>
        public object? AttachedObject { get; private set; }

        /// <summary>
        /// Gets the managed thread ID when Attach was called.
        /// </summary>
        public int? AttachThreadId { get; private set; }

        /// <summary>
        /// Gets the managed thread ID when Detach was called.
        /// </summary>
        public int? DetachThreadId { get; private set; }

        /// <summary>
        /// Gets the session identifier.
        /// </summary>
        public string? SessionId { get; private set; }

        /// <summary>
        /// Attaches the MXAccess COM object and records thread context.
        /// </summary>
        /// <param name="mxAccessComObject">MXAccess COM object to attach.</param>
        /// <param name="sessionId">Identifier of the session.</param>
        public void Attach(
            object mxAccessComObject,
            string sessionId)
        {
            AttachedObject = mxAccessComObject;
            AttachThreadId = Thread.CurrentThread.ManagedThreadId;
            SessionId = sessionId;
        }

        /// <summary>
        /// Detaches the MXAccess COM object and records thread context.
        /// </summary>
        public void Detach()
        {
            DetachThreadId = Thread.CurrentThread.ManagedThreadId;
            AttachedObject = null;
        }
    }

    /// <summary>
    /// Noop STA COM apartment initializer for testing.
    /// </summary>
    private sealed class NoopComApartmentInitializer : IStaComApartmentInitializer
    {
        /// <summary>
        /// Initializes the COM apartment (no-op).
        /// </summary>
        public void Initialize()
        {
        }

        /// <summary>
        /// Uninitializes the COM apartment (no-op).
        /// </summary>
        public void Uninitialize()
        {
        }
    }
}