Cosmos/source/Cosmos.Build.Builder/Collections/ObservableFixedSizeStack.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;

namespace Cosmos.Build.Builder.Collections
{
    internal class ObservableFixedSizeStack<T> : IEnumerable<T>, INotifyCollectionChanged
    {
        public event NotifyCollectionChangedEventHandler CollectionChanged;

        private T[] _items;
        private int _itemCount;

        public ObservableFixedSizeStack(int size)
        {
            if (size < 1)
            {
                throw new ArgumentOutOfRangeException(nameof(size));
            }

            _items = new T[size];
        }

        public void Push(T item)
        {
            if (_itemCount < _items.Length)
            {
                _items[_itemCount] = item;
                _itemCount++;
            }
            else
            {
                Array.Copy(_items, 1, _items, 0, _items.Length - 1);
                _items[_items.Length - 1] = item;
            }

            OnCollectionChanged();
        }

        public void Clear()
        {
            _itemCount = 0;
            Array.Clear(_items, 0, _items.Length);
        }

        private void OnCollectionChanged() => CollectionChanged?.Invoke(
            this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));

        public IEnumerator<T> GetEnumerator() => ((IEnumerable<T>)_items).GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => _items.GetEnumerator();
    }
}