// 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.Collections.Immutable;
using System.Runtime.InteropServices;
 
namespace Microsoft.CodeAnalysis
{
    internal static class GlobalAssemblyCacheLocation
    {
        internal enum ASM_CACHE
        {
            ZAP = 0x1,
            GAC = 0x2,                // C:\Windows\Assembly\GAC
            DOWNLOAD = 0x4,
            ROOT = 0x8,               // C:\Windows\Assembly
            GAC_MSIL = 0x10,
            GAC_32 = 0x20,            // C:\Windows\Assembly\GAC_32
            GAC_64 = 0x40,            // C:\Windows\Assembly\GAC_64
            ROOT_EX = 0x80,           // C:\Windows\Microsoft.NET\assembly
        }
 
        [DllImport("clr", PreserveSig = true)]
        private static extern unsafe int GetCachePath(ASM_CACHE id, byte* path, ref int length);
 
        public static ImmutableArray<string> s_rootLocations;
 
        public static ImmutableArray<string> RootLocations
        {
            get
            {
                if (s_rootLocations.IsDefault)
                {
                    s_rootLocations = ImmutableArray.Create(GetLocation(ASM_CACHE.ROOT), GetLocation(ASM_CACHE.ROOT_EX));
                }
 
                return s_rootLocations;
            }
        }
 
        private static unsafe string GetLocation(ASM_CACHE gacId)
        {
            const int ERROR_INSUFFICIENT_BUFFER = unchecked((int)0x8007007A);
 
            int characterCount = 0;
            int hr = GetCachePath(gacId, null, ref characterCount);
            if (hr != ERROR_INSUFFICIENT_BUFFER)
            {
                throw Marshal.GetExceptionForHR(hr);
            }
 
            byte[] data = new byte[(characterCount + 1) * 2];
            fixed (byte* p = data)
            {
                hr = GetCachePath(gacId, p, ref characterCount);
                if (hr != 0)
                {
                    throw Marshal.GetExceptionForHR(hr);
                }
 
                return Marshal.PtrToStringUni((IntPtr)p);
            }
        }
    }
}