using System.Linq;

namespace System.Collections.Generic
{
    public class OrderedList<T>: IEnumerable<T>, ICollection<T>
        where T : notnull
    {
        private readonly List<T> list = new List<T>();

        private readonly Func<T, object> keySelector;
        private readonly bool isDescending = false;

        private IOrderedEnumerable<T> OrdredList => isDescending
            ? list.OrderByDescending(keySelector)
            : list.OrderBy(keySelector);

        public int Count => list.Count;

        public bool IsReadOnly => false;

        public OrderedList(Func<T, object> keySelector, bool isDescending = false)
        {
            this.keySelector = keySelector;
            this.isDescending = isDescending;
        }

        public void Add(T item) => list.Add(item);

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

        public bool Contains(T item)=>  list.Contains(item);

        public void CopyTo(T[] array, int arrayIndex)=> list.CopyTo(array, arrayIndex);

        public bool Remove(T item)=> list.Remove(item);

        public IEnumerator<T> GetEnumerator() => OrdredList.GetEnumerator();

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }
}