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 jakarta.jms.MessageListener;
  
  import org.apache.activemq.command.ActiveMQDestination;
  import org.apache.activemq.command.Message;
  
  /**
   * Represents some kind of query which will load initial messages from some source for a new topic subscriber.
   * 
   * 
   */
  public interface MessageQuery {
      
      /**
       * Executes the query for messages; each message is passed into the listener
       * 
       * @param destination the destination on which the query is to be performed
       * @param listener is the listener to notify as each message is created or loaded
       */
      void execute(ActiveMQDestination destination, MessageListener listener) throws Exception;
  
      /**
       * Returns true if the given update is valid and does not overlap with the initial message query.
       * When performing an initial load from some source, there is a chance that an update may occur which is logically before
       * the message sent on the initial load - so this method provides a hook where the query instance can keep track of the version IDs
       * of the messages sent so that if an older version is sent as an update it can be excluded to avoid going backwards in time.
       * 
       * e.g. if the execute() method creates version 2 of an object and then an update message is sent for version 1, this method should return false to 
       * hide the old update message.
       * 
       * @param message the update message which may have been sent before the query actually completed
       * @return true if the update message is valid otherwise false in which case the update message will be discarded.
       */
      boolean validateUpdate(Message message);
  
  }
  