Iteratorパターン練習2

using System.Collections.Generic;

namespace Iterator3
{
	public class BookShelf : Shelf<Book>
	{
		public Book GetRandom ()
		{
			int index = new System.Random ().Next (GetCount ());
			return GetAt (index);
		}
	}

	public class AnimeShelf : Shelf<DVD>
	{
		public DVD GetRandom ()
		{
			int index = new System.Random ().Next (GetCount ());
			return GetAt (index);
		}
	}

	public abstract class Shelf<T> : Aggeregate<T>
	{
		List<T> items = new List<T> ();

		public T GetAt (int index)
		{
			return items [index];
		}

		public void Add (T data)
		{
			items.Add (data);
		}

		public void RemoveAt (int index)
		{
			items.RemoveAt (index);
		}

		public int GetCount ()
		{
			return items.Count;
		}

		public Iterator<T> Iterator ()
		{
			return new ShelfIterator<Shelf<T>,T> (this);
		}
	}

	public class ShelfIterator<T1,T2> : Iterator<T2> where T1 : Shelf<T2>
	{
		private T1 shelf;
		private int index;

		public ShelfIterator (T1 shelf)
		{
			this.shelf = shelf;
		}

		public bool HasNext ()
		{
			return index < shelf.GetCount ();
		}

		public T2 Next ()
		{
			var item = shelf.GetAt (index);
			index++;
			return item;
		}
	
	}

}