namespace WxAgent.Core;

/// <summary>Serializes commands locally and across processes; the OS releases the file handle after a crash.</summary>
public sealed class InterprocessCommandGate : IDisposable
{
    private readonly SemaphoreSlim _local = new(1, 1);
    private readonly string _path;
    private FileStream? _lease;

    public InterprocessCommandGate(string path)
    {
        _path = Path.GetFullPath(path);
        Directory.CreateDirectory(Path.GetDirectoryName(_path)!);
    }

    public async Task WaitAsync(CancellationToken cancellationToken)
    {
        await _local.WaitAsync(cancellationToken).ConfigureAwait(false);
        try
        {
            while (true)
            {
                cancellationToken.ThrowIfCancellationRequested();
                try
                {
                    _lease = new FileStream(_path, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
                    return;
                }
                catch (IOException exception) when ((exception.HResult & 0xffff) is 11 or 32 or 33)
                {
                    // EAGAIN on Unix; sharing/lock violation on Windows. Other I/O errors must surface.
                    await Task.Delay(50, cancellationToken).ConfigureAwait(false);
                }
            }
        }
        catch
        {
            _local.Release();
            throw;
        }
    }

    public void Release()
    {
        try { _lease?.Dispose(); }
        finally
        {
            _lease = null;
            _local.Release();
        }
    }

    public void Dispose()
    {
        _lease?.Dispose();
        _local.Dispose();
    }
}