// 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.Collections;
using System.Collections.Generic;

namespace Microsoft.CodeAnalysis.Utilities;

internal static class IReadOnlyListExtensions
{
    public static IReadOnlyList<T> ToReadOnlyList<T>(this IList<T> list)
    {
        if (list is IReadOnlyList<T> readOnlyList)
        {
            return readOnlyList;
        }

        return new ReadOnlyList<T>(list);
    }

    public static T Last<T>(this IReadOnlyList<T> list)
        => list[list.Count - 1];

    public static int IndexOf<T>(this IReadOnlyList<T> list, T value, int startIndex = 0)
    {
        for (var index = startIndex; index < list.Count; index++)
        {
            if (EqualityComparer<T>.Default.Equals(list[index], value))
            {
                return index;
            }
        }

        return -1;
    }

    private sealed class ReadOnlyList<T>(IList<T> list) : IReadOnlyList<T>
    {
        public T this[int index] => list[index];
        public int Count => list.Count;
        public IEnumerator<T> GetEnumerator() => list.GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => list.GetEnumerator();
    }
}