content: /*
   * Copyright (C) 2010-2101 Alibaba Group Holding Limited.
   *
   * 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.otter.shared.common.utils.cache;
  
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Set;
  import java.util.Map.Entry;
  
  import com.google.common.collect.MapMaker;
  
  /**
   * 简单内存镜像实现
   * 
   * <pre>
   * 1. 使用hashMap做为存储
   * 2. 支持时间戳作为版本号
   * 3. 支持ComputeFunction，在get结果为null允许进行回调处理
   * </pre>
   */
  public class ExtensionMemoryMirror<KEY, VALUE> {
  
      private final Map<KEY, VALUE>             store;
      private final ComputeFunction<KEY, VALUE> function;
  
      public ExtensionMemoryMirror(ComputeFunction<KEY, VALUE> function){
          this.function = function;
          store = new MapMaker().makeMap();
      }
  
      public synchronized VALUE get(KEY key) {
          if (store.containsKey(key)) {
              KEY oldKey = null;
              for (KEY k : store.keySet()) {
                  if (k.equals(key)) {
                      oldKey = k;
                      break;
                  }
              }
  
              if (((Comparable) key).compareTo(oldKey) > 0) {
                  VALUE result = function.apply(key);
                  // 一定要先删除key，否则put时key不会被更新，对应的时间戳一直为老对象
                  remove(key);
                  put(key, result);
                  return result;
              } else {
                  return store.get(key);
              }
          } else {
              VALUE result = function.apply(key);
              remove(key);
              put(key, result);
              return result;
          }
  
      }
  
      public synchronized void put(KEY key, VALUE value) {
          store.put(getKey(key), value);
      }
  
      public synchronized void remove(Object key) {
          store.remove(getKey(key));
      }
  
      public synchronized void clear() {
          store.clear();
      }
  
      public Iterator getKeys() {
          return store.keySet().iterator();
      }
  
      public Set<Entry<KEY, VALUE>> entrySet() {
          return store.entrySet();
      }
  
      public int size() {
          return store.size();
      }
  
      private KEY getKey(Object key) {
          if (key == null) {
              throw new IllegalArgumentException("Cache key not be null");
          }
  
          return (KEY) key;
      }
  
      public static interface ComputeFunction<KEY, VALUE> {
  
          VALUE apply(KEY key);
  
      }
  
  }
  