/*----------------------------------------------------------

This Source Code Form is subject to the terms of the

Mozilla Public License, v.2.0. If a copy of the MPL

was not distributed with this file, You can obtain one

at http://mozilla.org/MPL/2.0/.

----------------------------------------------------------*/

using System;

using System.Collections.Generic;

namespace ScriptEngine.Machine

{

public class LruCache<TKey, TValue>

{

private readonly int _capacity;

private readonly Dictionary<TKey, LinkedListNode<CacheItem>> _index =

new Dictionary<TKey, LinkedListNode<CacheItem>>();

private readonly LinkedList<CacheItem> _list = new LinkedList<CacheItem>();

public LruCache(int capacity)

{

_capacity = capacity;

}

public bool IsEmpty() => _index.Count == 0;

public void Clear()

{

_index.Clear();

_list.Clear();

}

public TValue GetOrAdd(TKey key, Func<TKey, TValue> factory)

{

if (_index.TryGetValue(key, out var listNode))

{

_list.Remove(listNode);

_list.AddFirst(listNode);

return listNode.Value.Value;

}

if (_index.Count == _capacity)

{

var keyOfOld = _list.Last.Value.Key;

_index.Remove(keyOfOld);

_list.RemoveLast();

}

var newItem = _list.AddFirst(CacheItem.Create(key, factory(key)));

_index[key] = newItem;

return newItem.Value.Value;

}

private class CacheItem

{

public static CacheItem Create(TKey key, TValue value) =>

new CacheItem(key, value);

private CacheItem(TKey key, TValue value)

{

Key = key;

Value = value;

}

public TKey Key { get; }

public TValue Value { get; }

}

}

}