content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * 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 com.alibaba.nacos.common.cache.decorators;
  
  import com.alibaba.nacos.common.cache.Cache;
  
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.concurrent.Callable;
  
  /**
   * A wrapper that lru cache.
   * @author zzq
   * @date 2021/7/30
   */
  public class LruCache<K, V> implements Cache<K, V> {
      
      private final Cache<K, V> delegate;
      
      private Map<K, V> keyMap;
      
      private K eldestKey;
      
      public LruCache(Cache<K, V> delegate, int size) {
          this.delegate = delegate;
          setSize(size);
      }
      
      @Override
      public int getSize() {
          return delegate.getSize();
      }
      
      public void setSize(final int size) {
          keyMap = new LinkedHashMap<K, V>(size, .75F, true) {
              private static final long serialVersionUID = 4267176411845948333L;
              
              @Override
              protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
                  boolean tooBig = size() > size;
                  if (tooBig) {
                      eldestKey = eldest.getKey();
                  }
                  return tooBig;
              }
            
          };
      }
      
      @Override
      public void put(K key, V val) {
          delegate.put(key, val);
          cycleKeyList(key);
      }
      
      @Override
      public V get(K key) {
          keyMap.get(key);
          return delegate.get(key);
      }
      
      @Override
      public V get(K key, Callable<? extends V> call) throws Exception {
          return this.delegate.get(key, call);
      }
      
      @Override
      public V remove(K key) {
          return delegate.remove(key);
      }
      
      @Override
      public void clear() {
          delegate.clear();
          keyMap.clear();
      }
      
      private void cycleKeyList(K key) {
          keyMap.put(key, null);
          if (eldestKey != null) {
              delegate.remove(eldestKey);
              eldestKey = null;
          }
      }
      
  }
  