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

namespace PgRr.System.Collections.Generic {
    public class UniqueQueue<T> : IEnumerable<T>, IEnumerable {

        private HashSet<T> hashSet = new HashSet<T>();
        private Queue<T> queue = new Queue<T>();

        public int Count => hashSet.Count;

        public void Clear() {
            hashSet.Clear();
            queue.Clear();
        }

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

        public void Enqueue(T item) {
            if (hashSet.Add(item)) {
                queue.Enqueue(item);
            } else {
                throw new InvalidOperationException("The queue already contains this item");
            }
        }

        public T Dequeue() {
            T item = queue.Dequeue();
            hashSet.Remove(item);
            return item;
        }

        public T Peek() => queue.Peek();

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

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

    }
}