// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System;
using System.Runtime.InteropServices;
 
namespace Microsoft.VisualStudio.LanguageServices.CSharp.ProjectSystemShim
{
    /// <summary>
    /// This is a terrible, terrible hack around the C# project system in
    /// CCscMSBuildHostObject::SetDelaySign. To indicate a value of "unset"
    /// for boolean options, they create variant of type VT_BOOL with the boolean
    /// field being a value of "4". The CLR, if it marshals this variant, marshals
    /// it as a "true" which is indistinguishable from a real VARIANT_TRUE. So
    /// instead we define this structure of the same layout, and marshal the variant
    /// as this structure. We can then pick out this broken pattern, and convert
    /// it to null instead of true.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal readonly struct HACK_VariantStructure
    {
        private readonly short _type;
 
        private readonly short _padding1;
        private readonly short _padding2;
        private readonly short _padding3;
 
        private readonly short _booleanValue;
        private readonly IntPtr _padding4; // this will be aligned to the IntPtr-sized address
 
        public unsafe object ConvertToObject()
        {
            if (_type == (short)VarEnum.VT_BOOL && _booleanValue == 4)
            {
                return null;
            }
 
            // Can't take an address of this since it might move, so....
            var localCopy = this;
            return Marshal.GetObjectForNativeVariant((IntPtr)(&localCopy));
        }
    }
}