/*
    *    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.Deque;
  import java.util.LinkedList;
  
  import org.apache.ibatis.cache.Cache;
  
  /**
   * FIFO (first in, first out) cache decorator.
   *
   * @author Clinton Begin
   */
  public class FifoCache implements Cache {
  
    private final Cache delegate;
    private final Deque<Object> keyList;
    private int size;
  
    public FifoCache(Cache delegate) {
      this.delegate = delegate;
      this.keyList = new LinkedList<>();
      this.size = 1024;
    }
  
    @Override
    public String getId() {
      return delegate.getId();
    }
  
    @Override
    public int getSize() {
      return delegate.getSize();
    }
  
    public void setSize(int size) {
      this.size = size;
    }
  
    @Override
    public void putObject(Object key, Object value) {
      cycleKeyList(key);
      delegate.putObject(key, value);
    }
  
    @Override
    public Object getObject(Object key) {
      return delegate.getObject(key);
    }
  
    @Override
    public Object removeObject(Object key) {
      return delegate.removeObject(key);
    }
  
    @Override
    public void clear() {
      delegate.clear();
      keyList.clear();
    }
  
    private void cycleKeyList(Object key) {
      keyList.addLast(key);
      if (keyList.size() > size) {
        Object oldestKey = keyList.removeFirst();
        delegate.removeObject(oldestKey);
      }
    }
  
  }