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.ambari.server.agent.stomp;
  
  import java.util.Objects;
  
  import jakarta.inject.Inject;
  
  import org.apache.ambari.server.AmbariException;
  import org.apache.ambari.server.agent.stomp.dto.Hashable;
  import org.apache.ambari.server.events.STOMPEvent;
  import org.apache.ambari.server.events.publishers.STOMPUpdatePublisher;
  
  /**
   * Is used to saving and updating last version of event in cluster scope
   * @param <T> event with hash to control version
   */
  public abstract class AgentClusterDataHolder<T extends STOMPEvent & Hashable> extends AgentDataHolder<T> {
  
    @Inject
    protected STOMPUpdatePublisher STOMPUpdatePublisher;
  
    private volatile T data;
  
    public T getUpdateIfChanged(String agentHash) throws AmbariException {
      initializeDataIfNeeded(true);
      return !Objects.equals(agentHash, data.getHash()) ? data : getEmptyData();
    }
  
    /**
     * Builds an update with the full set of current data.
     * The eventType should be "CREATE", if applicable.
     */
    protected abstract T getCurrentData() throws AmbariException;
  
    /**
     * Handle an incremental update to the data.
     * @return true if the update introduced any change
     */
    protected abstract boolean handleUpdate(T update) throws AmbariException;
  
    /**
     * Template method to update the data.
     * @return true if the update introduced any change
     */
    public boolean updateData(T update) throws AmbariException {
      updateLock.lock();
      try {
        initializeDataIfNeeded(true);
        boolean changed = handleUpdate(update);
        if (changed) {
          regenerateDataIdentifiers(data);
          update.setHash(getData().getHash());
          STOMPUpdatePublisher.publish(update);
        }
        return changed;
      } finally {
        updateLock.unlock();
      }
    }
  
    protected final void initializeDataIfNeeded(boolean regenerateHash) throws AmbariException {
      if (data == null) {
        updateLock.lock();
        try {
          if (data == null) {
            T localData = getCurrentData();
            if (regenerateHash) {
              regenerateDataIdentifiers(localData);
            }
            data = localData;
          }
        } finally {
          updateLock.unlock();
        }
      }
    }
  
    public final T getData() {
      return data;
    }
  
  }
  