Umbraco-CMS/src/Umbraco.Core/Collections/StackQueue.cs

namespace Umbraco.Cms.Core.Collections
{
    /// <summary>
    ///     Collection that can be both a queue and a stack.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class StackQueue<T>
    {
        private readonly LinkedList<T?> _linkedList = new ();

        public int Count => _linkedList.Count;

        public void Clear() => _linkedList.Clear();

        public void Push(T? obj) => _linkedList.AddFirst(obj);

        public void Enqueue(T? obj) => _linkedList.AddFirst(obj);

        public T Pop()
        {
            T? obj = default(T);
            if (_linkedList.First is not null)
            {
                obj = _linkedList.First.Value;
            }
            _linkedList.RemoveFirst();
            return obj!;
        }

        public T Dequeue()
        {
            T? obj = default(T);
            if (_linkedList.Last is not null)
            {
                obj = _linkedList.Last.Value;
            }
            _linkedList.RemoveLast();
            return obj!;
        }

        public T? PeekStack() => _linkedList.First is not null ? _linkedList.First.Value : default;

        public T? PeekQueue() => _linkedList.Last is not null ? _linkedList.Last.Value : default;
    }
}