SharpDx : implementation of include handler

IncludeHandler

class IncludeHandler : Include
{
    readonly string directoryName;

    public IncludeHandler(string directoryName)
    {
        this.directoryName = directoryName;
    }

    public void Dispose()
    {
    }

    public IDisposable Shadow { get; set; }

    public Stream Open(IncludeType type, string fileName, Stream parentStream)
    {
        switch (type)
        {
            case IncludeType.Local:
                string d = parentStream switch
                {
                    null => directoryName,
                    FileStream fileStream => Path.GetDirectoryName(fileStream.Name),
                    _ => throw new NotSupportedException()
                };
                return File.OpenRead(Path.Combine(d, fileName));

            default:
                throw new ArgumentOutOfRangeException(nameof(type), type, null);
        }
    }

    public void Close(Stream stream)
    {
        stream.Close();
    }
}