using System;
namespace ln.collections
{
	public class Cache<K,V>
	{
		public int Count => values.Count;

		BTree<K, V> values;
		BTree<K, LinkedListItem<K>> itemTree;
		LinkedList<K> items = new LinkedList<K>();

        int maxCacheSize = 4096;

		public Cache()
		{
			values = new BTree<K, V>();
			itemTree = new BTree<K, LinkedListItem<K>>();
		}
		public Cache(Comparison<K> compare)
		{
			values = new BTree<K, V>(compare);
			itemTree = new BTree<K, LinkedListItem<K>>(compare);
		}

		public int MaxCacheSize
		{
			get => maxCacheSize;
			set {
				maxCacheSize = value;
				while (maxCacheSize < values.Count)
				{
					Forget();
				}
			}
		}

		public void Clear()
		{
			values.Clear();
			itemTree.Clear();
			items.Clear();
		}

		public bool TryGet(K key,out V value)
		{
			return values.TryGet(key, out value);
		}

		public void Forget()
		{
			lock (this)
			{
				Forget(items.FirstItem);
			}
		}
		public void Forget(K key)
		{
			lock (this)
			{
				if (itemTree.TryGet(key,out LinkedListItem<K> item))
					Forget(item);
			}
		}

		private void Forget(LinkedListItem<K> item)
		{
			if (item == null)
				return;

			values.Remove(item.Value);
			itemTree.Remove(item.Value);
			items.Remove(item);
		}

		public void Ensure(K key,V value)
		{
			lock (this)
			{
				if (!itemTree.TryGet(key, out LinkedListItem<K> item))
				{
					item = new LinkedListItem<K>(key);
					values.Add(key,value);
				}
				Ensure(item);
			}
		}

		private void Ensure(LinkedListItem<K> item)
		{
			if (!item.IsLinked)
				itemTree.Add(item.Value, item);
			items.Add(item);
		}

	}
}