using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using MxGateway.Contracts.Proto;
using MxGateway.Worker.Sta;

namespace MxGateway.Worker.MxAccess;

public sealed class MxAccessStaSession : IWorkerRuntimeSession
{
    private readonly IMxAccessComObjectFactory factory;
    private readonly IMxAccessEventSink eventSink;
    private readonly MxAccessEventQueue eventQueue;
    private readonly StaRuntime staRuntime;
    private StaCommandDispatcher? commandDispatcher;
    private MxAccessSession? session;
    private bool disposed;

    public MxAccessStaSession()
        : this(
            new StaRuntime(),
            new MxAccessComObjectFactory(),
            new MxAccessEventQueue())
    {
    }

    public MxAccessStaSession(
        StaRuntime staRuntime,
        IMxAccessComObjectFactory factory,
        IMxAccessEventSink eventSink)
        : this(staRuntime, factory, eventSink, new MxAccessEventQueue())
    {
    }

    public MxAccessStaSession(
        StaRuntime staRuntime,
        IMxAccessComObjectFactory factory,
        MxAccessEventQueue eventQueue)
        : this(staRuntime, factory, new MxAccessBaseEventSink(eventQueue), eventQueue)
    {
    }

    public MxAccessStaSession(
        StaRuntime staRuntime,
        IMxAccessComObjectFactory factory,
        IMxAccessEventSink eventSink,
        MxAccessEventQueue eventQueue)
    {
        this.staRuntime = staRuntime ?? throw new ArgumentNullException(nameof(staRuntime));
        this.factory = factory ?? throw new ArgumentNullException(nameof(factory));
        this.eventSink = eventSink ?? throw new ArgumentNullException(nameof(eventSink));
        this.eventQueue = eventQueue ?? throw new ArgumentNullException(nameof(eventQueue));
    }

    public MxAccessEventQueue EventQueue => eventQueue;

    public Task<WorkerReady> StartAsync(
        int workerProcessId,
        CancellationToken cancellationToken = default)
    {
        return StartAsync(string.Empty, workerProcessId, cancellationToken);
    }

    public Task<WorkerReady> StartAsync(
        string sessionId,
        int workerProcessId,
        CancellationToken cancellationToken = default)
    {
        staRuntime.Start();

        return staRuntime.InvokeAsync(
            () =>
            {
                if (session is not null)
                {
                    throw new InvalidOperationException("MXAccess COM session has already been created.");
                }

                session = MxAccessSession.Create(factory, eventSink, sessionId);
                commandDispatcher = new StaCommandDispatcher(
                    staRuntime,
                    new MxAccessCommandExecutor(session));

                return session.CreateWorkerReady(workerProcessId);
            },
            cancellationToken);
    }

    public Task<MxCommandReply> DispatchAsync(StaCommand command)
    {
        if (commandDispatcher is null)
        {
            throw new InvalidOperationException("MXAccess COM session has not been started.");
        }

        return commandDispatcher.DispatchAsync(command);
    }

    public WorkerRuntimeHeartbeatSnapshot CaptureHeartbeat()
    {
        uint pendingCommandCount = 0;
        string currentCommandCorrelationId = string.Empty;

        if (commandDispatcher is not null)
        {
            pendingCommandCount = (uint)commandDispatcher.PendingCommandCount;
            currentCommandCorrelationId = commandDispatcher.CurrentCommandCorrelationId;
        }

        return new WorkerRuntimeHeartbeatSnapshot(
            staRuntime.LastActivityUtc,
            pendingCommandCount,
            (uint)eventQueue.Count,
            eventQueue.LastEventSequence,
            currentCommandCorrelationId);
    }

    public void RequestShutdown()
    {
        commandDispatcher?.RequestShutdown();
    }

    public IReadOnlyList<WorkerEvent> DrainEvents(uint maxEvents)
    {
        return eventQueue.Drain(maxEvents);
    }

    public Task<IReadOnlyList<RegisteredServerHandle>> GetRegisteredServerHandlesAsync(
        CancellationToken cancellationToken = default)
    {
        if (session is null)
        {
            throw new InvalidOperationException("MXAccess COM session has not been started.");
        }

        return staRuntime.InvokeAsync(
            () => session.HandleRegistry.ServerHandles,
            cancellationToken);
    }

    public Task<IReadOnlyList<RegisteredItemHandle>> GetRegisteredItemHandlesAsync(
        CancellationToken cancellationToken = default)
    {
        if (session is null)
        {
            throw new InvalidOperationException("MXAccess COM session has not been started.");
        }

        return staRuntime.InvokeAsync(
            () => session.HandleRegistry.ItemHandles,
            cancellationToken);
    }

    public Task<IReadOnlyList<RegisteredAdviceHandle>> GetRegisteredAdviceHandlesAsync(
        CancellationToken cancellationToken = default)
    {
        if (session is null)
        {
            throw new InvalidOperationException("MXAccess COM session has not been started.");
        }

        return staRuntime.InvokeAsync(
            () => session.HandleRegistry.AdviceHandles,
            cancellationToken);
    }

    public async Task<MxAccessShutdownResult> ShutdownGracefullyAsync(
        TimeSpan timeout,
        CancellationToken cancellationToken = default)
    {
        if (timeout <= TimeSpan.Zero)
        {
            throw new ArgumentOutOfRangeException(
                nameof(timeout),
                "MXAccess graceful shutdown timeout must be greater than zero.");
        }

        if (disposed)
        {
            return new MxAccessShutdownResult(Array.Empty<MxAccessShutdownFailure>());
        }

        commandDispatcher?.RequestShutdown();

        Stopwatch stopwatch = Stopwatch.StartNew();
        MxAccessShutdownResult result;
        if (session is null)
        {
            result = new MxAccessShutdownResult(Array.Empty<MxAccessShutdownFailure>());
        }
        else
        {
            using CancellationTokenSource shutdownCancellation =
                CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
            shutdownCancellation.CancelAfter(timeout);

            Task<MxAccessShutdownResult> cleanupTask = staRuntime.InvokeAsync(
                () => session.ShutdownGracefully(),
                shutdownCancellation.Token);
            Task delayTask = Task.Delay(timeout, cancellationToken);
            Task completedTask = await Task.WhenAny(cleanupTask, delayTask).ConfigureAwait(false);
            if (completedTask != cleanupTask)
            {
                cancellationToken.ThrowIfCancellationRequested();
                throw new TimeoutException($"MXAccess graceful shutdown exceeded {timeout}.");
            }

            result = await cleanupTask.ConfigureAwait(false);
        }

        TimeSpan remaining = timeout - stopwatch.Elapsed;
        if (remaining <= TimeSpan.Zero || !staRuntime.Shutdown(remaining))
        {
            throw new TimeoutException($"MXAccess graceful shutdown exceeded {timeout}.");
        }

        staRuntime.Dispose();
        disposed = true;
        return result;
    }

    public void Dispose()
    {
        if (disposed)
        {
            return;
        }

        RequestShutdown();

        if (session is not null)
        {
            staRuntime.InvokeAsync(() => session.Dispose()).GetAwaiter().GetResult();
        }

        staRuntime.Dispose();
        disposed = true;
    }
}