content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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.activemq.broker.region.policy;
  
  import org.apache.activemq.broker.region.MessageReference;
  
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  
  /**
   * An eviction strategy which evicts the oldest message within messages with the same property value
   *
   *
   * @org.apache.xbean.XBean
   *
   */
  public class UniquePropertyMessageEvictionStrategy extends MessageEvictionStrategySupport {
  
      protected String propertyName;
  
      public String getPropertyName() {
          return propertyName;
      }
  
      public void setPropertyName(String propertyName) {
          this.propertyName = propertyName;
      }
  
      @Override
      public MessageReference[] evictMessages(LinkedList messages) throws IOException {
          List<MessageReference> messageReferences = new LinkedList<>(messages);
          HashMap<Object, MessageReference> pivots = new HashMap<>();
  
          for (MessageReference reference : messageReferences) {
              if (propertyName != null && reference.getMessage().getProperty(propertyName) != null) {
                  Object key = reference.getMessage().getProperty(propertyName);
                  if (pivots.containsKey(key)) {
                      MessageReference pivot = pivots.get(key);
                      if (reference.getMessage().getTimestamp() > pivot.getMessage().getTimestamp()) {
                           pivots.put(key, reference);
                      }
                  } else {
                      pivots.put(key, reference);
                  }
              }
          }
  
          if (pivots.isEmpty() || pivots.values().size() == messageReferences.size()) {
              return new MessageReference[]{(MessageReference) messages.removeFirst()};
          } else {
              messages.removeIf(message -> !pivots.containsValue(message));
              messageReferences.removeAll(pivots.values());
              return messageReferences.toArray(new MessageReference[0]);
          }
      }
  
  }
  