using System;
using System.Collections.Generic;

namespace cakeslice
{
    /// <summary>
    /// A collection with the fast iteration time of a List and the no-duplicates and fast Remove/Contains time of a HashSet.
    /// </summary>
	public class LinkedSet<T> : IEnumerable<T>
	{
		private LinkedList<T> list;
		private Dictionary<T, LinkedListNode<T>> dictionary;

		public LinkedSet()
		{
			list = new LinkedList<T>();
			dictionary = new Dictionary<T, LinkedListNode<T>>();
		}

		public LinkedSet(IEqualityComparer<T> comparer)
		{
			list = new LinkedList<T>();
			dictionary = new Dictionary<T, LinkedListNode<T>>(comparer);
		}
		
        /// <summary>
        /// returns true if the item did not already exist in the LinkedSet
        /// </summary>
		public bool Add(T t)
		{
			if (dictionary.ContainsKey(t))
				return false;

			LinkedListNode<T> node = list.AddLast(t);
			dictionary.Add(t, node);
			return true;
		}

        /// <summary>
        /// returns true if the item did previously exist in the LinkedSet
        /// </summary>
        public bool Remove(T t)
        {
            LinkedListNode<T> node;

            if (dictionary.TryGetValue(t, out node))
            {
                dictionary.Remove(t);
                list.Remove(node);
                return true;
            }
            else
            {
                return false;
            }
        }

        public void Clear()
		{
			list.Clear();
			dictionary.Clear();
		}

        public bool Contains(T t)
            => dictionary.ContainsKey(t);

        public int Count
            => list.Count;

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

		System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
		    => list.GetEnumerator();
	}
}