using System.Runtime.InteropServices;

namespace ProtonVPN.OperatingSystems.WebAuthn.Interop.Marshalers;

public static class VersionedStructMarshaler
{
    public static T PtrToStructure<T>(nint ptr, int sourceStructSize) where T : class
    {
        if (ptr == nint.Zero || sourceStructSize == 0)
        {
            return null;
        }

        if (sourceStructSize < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(sourceStructSize));
        }

        int targetStructSize = Marshal.SizeOf<T>();

        if (sourceStructSize >= targetStructSize)
        {
            // Structure formats are incremental, so it does not matter if the source structure is larger.
            return Marshal.PtrToStructure<T>(ptr);
        }
        else
        {
            // We first need to copy the native structure to a larger zero-filled buffer
            byte[] buffer = new byte[targetStructSize];
            Marshal.Copy(ptr, buffer, 0, sourceStructSize);
            GCHandle bufferHandle = GCHandle.Alloc(buffer, GCHandleType.Pinned);

            try
            {
                return Marshal.PtrToStructure<T>(bufferHandle.AddrOfPinnedObject());
            }
            finally
            {
                bufferHandle.Free();
            }
        }
    }
}