/*
    *    Copyright 2009-2021 the original author or authors.
    *
    *    Licensed under the Apache License, Version 2.0 (the "License");
    *    you may not use this file except in compliance with the License.
    *    You may obtain a copy of the License at
    *
    *       http://www.apache.org/licenses/LICENSE-2.0
    *
   *    Unless required by applicable law or agreed to in writing, software
   *    distributed under the License is distributed on an "AS IS" BASIS,
   *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *    See the License for the specific language governing permissions and
   *    limitations under the License.
   */
  package org.apache.ibatis.cache.decorators;
  
  import java.util.LinkedHashMap;
  import java.util.Map;
  
  import org.apache.ibatis.cache.Cache;
  
  /**
   * Lru (least recently used) cache decorator.
   *
   * @author Clinton Begin
   */
  public class LruCache implements Cache {
  
    private final Cache delegate;
    private Map<Object, Object> keyMap;
    private Object eldestKey;
  
    public LruCache(Cache delegate) {
      this.delegate = delegate;
      setSize(1024);
    }
  
    @Override
    public String getId() {
      return delegate.getId();
    }
  
    @Override
    public int getSize() {
      return delegate.getSize();
    }
  
    public void setSize(final int size) {
      keyMap = new LinkedHashMap<Object, Object>(size, .75F, true) {
        private static final long serialVersionUID = 4267176411845948333L;
  
        @Override
        protected boolean removeEldestEntry(Map.Entry<Object, Object> eldest) {
          boolean tooBig = size() > size;
          if (tooBig) {
            eldestKey = eldest.getKey();
          }
          return tooBig;
        }
      };
    }
  
    @Override
    public void putObject(Object key, Object value) {
      delegate.putObject(key, value);
      cycleKeyList(key);
    }
  
    @Override
    public Object getObject(Object key) {
      keyMap.get(key); // touch
      return delegate.getObject(key);
    }
  
    @Override
    public Object removeObject(Object key) {
      return delegate.removeObject(key);
    }
  
    @Override
    public void clear() {
      delegate.clear();
      keyMap.clear();
    }
  
    private void cycleKeyList(Object key) {
      keyMap.put(key, key);
      if (eldestKey != null) {
        delegate.removeObject(eldestKey);
        eldestKey = null;
      }
    }
  
  }