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.advisory;
  
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import jakarta.jms.Connection;
  import jakarta.jms.Destination;
  import jakarta.jms.JMSException;
  import jakarta.jms.Message;
  import jakarta.jms.MessageListener;
  import jakarta.jms.Session;
  
  import org.apache.activemq.ActiveMQMessageConsumer;
  import org.apache.activemq.Service;
  import org.apache.activemq.command.ActiveMQDestination;
  import org.apache.activemq.command.ActiveMQMessage;
  import org.apache.activemq.command.ActiveMQTopic;
  import org.apache.activemq.command.ConsumerId;
  import org.apache.activemq.command.ConsumerInfo;
  import org.apache.activemq.command.RemoveInfo;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * An object which can be used to listen to the number of active consumers
   * available on a given destination.
   * 
   * 
   */
  public class ConsumerEventSource implements Service, MessageListener {
      private static final Logger LOG = LoggerFactory.getLogger(ConsumerEventSource.class);
  
      private final Connection connection;
      private final ActiveMQDestination destination;
      private ConsumerListener listener;
      private AtomicBoolean started = new AtomicBoolean(false);
      private AtomicInteger consumerCount = new AtomicInteger();
      private Session session;
      private ActiveMQMessageConsumer consumer;
  
      public ConsumerEventSource(Connection connection, Destination destination) throws JMSException {
          this.connection = connection;
          this.destination = ActiveMQDestination.transform(destination);
      }
  
      public void setConsumerListener(ConsumerListener listener) {
          this.listener = listener;
      }
      
      public String getConsumerId() {
          return consumer != null ? consumer.getConsumerId().toString() : "NOT_SET";
      }
  
      public void start() throws Exception {
          if (started.compareAndSet(false, true)) {
              session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
              ActiveMQTopic advisoryTopic = AdvisorySupport.getConsumerAdvisoryTopic(destination);
              consumer = (ActiveMQMessageConsumer) session.createConsumer(advisoryTopic);
              consumer.setMessageListener(this);
          }
      }
  
      public void stop() throws Exception {
          if (started.compareAndSet(true, false)) {
              if (session != null) {
                  session.close();
              }
          }
      }
  
      public void onMessage(Message message) {
          if (message instanceof ActiveMQMessage) {
              ActiveMQMessage activeMessage = (ActiveMQMessage)message;
              Object command = activeMessage.getDataStructure();
              int count = 0;
              if (command instanceof ConsumerInfo) {
                  count = consumerCount.incrementAndGet();
                  count = extractConsumerCountFromMessage(message, count);
                  fireConsumerEvent(new ConsumerStartedEvent(this, destination, (ConsumerInfo)command, count));
              } else if (command instanceof RemoveInfo) {
                  RemoveInfo removeInfo = (RemoveInfo)command;
                  if (removeInfo.isConsumerRemove()) {
                      count = consumerCount.decrementAndGet();
                      count = extractConsumerCountFromMessage(message, count);
                      fireConsumerEvent(new ConsumerStoppedEvent(this, destination, (ConsumerId)removeInfo.getObjectId(), count));
                  }
              } else {
                  LOG.warn("Unknown command: " + command);
              }
          } else {
              LOG.warn("Unknown message type: " + message + ". Message ignored");
          }
      }
  
      /**
       * Lets rely by default on the broker telling us what the consumer count is
       * as it can ensure that we are up to date at all times and have not
       * received messages out of order etc.
       */
      protected int extractConsumerCountFromMessage(Message message, int count) {
          try {
              Object value = message.getObjectProperty("consumerCount");
              if (value instanceof Number) {
                  Number n = (Number)value;
                  return n.intValue();
              }
              LOG.warn("No consumerCount header available on the message: " + message);
          } catch (Exception e) {
              LOG.warn("Failed to extract consumerCount from message: " + message + ".Reason: " + e, e);
          }
          return count;
      }
  
      protected void fireConsumerEvent(ConsumerEvent event) {
          if (listener != null) {
              listener.onConsumerEvent(event);
          }
      }
  
  }
  