// 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.

using System;
using System.Collections.Generic;

namespace Microsoft.CodeAnalysis.Shared.Extensions;

internal static class IComparerExtensions
{
    public static IComparer<T> Inverse<T>(this IComparer<T> comparer)
    {
        if (comparer == null)
        {
            throw new ArgumentNullException(nameof(comparer));
        }

        return new InverseComparer<T>(comparer);
    }

    private sealed class InverseComparer<T> : IComparer<T>
    {
        private readonly IComparer<T> _comparer;

        internal InverseComparer(IComparer<T> comparer)
            => _comparer = comparer;

        public int Compare(T? x, T? y)
            => _comparer.Compare(y, x);
    }
}