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Apache Solr (module: core)
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/*
 * 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.solr.cluster.events;

import java.io.Closeable;
import org.apache.solr.cloud.ClusterSingleton;

/** Component that produces {@link ClusterEvent} instances. */
public interface ClusterEventProducer extends ClusterSingleton, Closeable {

  /** Unique name for the registration of a plugin-based implementation. */
  String PLUGIN_NAME = ".cluster-event-producer";

  @Override
  default String getName() {
    return PLUGIN_NAME;
  }

  /**
   * Register an event listener for processing the specified event types.
   *
   * @param listener non-null listener. If the same instance of the listener is already registered
   *     for some event types then it will be also registered for additional event types specified
   *     in this call.
   * @param eventTypes event types that this listener is being registered for. If this is null or
   *     empty then all types will be used.
   */
  void registerListener(ClusterEventListener listener, ClusterEvent.EventType... eventTypes);

  /**
   * Unregister an event listener for all event types.
   *
   * @param listener non-null listener.
   */
  default void unregisterListener(ClusterEventListener listener) {
    unregisterListener(listener, ClusterEvent.EventType.values());
  }

  /**
   * Unregister an event listener for specified event types.
   *
   * @param listener non-null listener.
   * @param eventTypes event types from which the listener will be unregistered. If this is null or
   *     empty then all event types will be used
   */
  void unregisterListener(ClusterEventListener listener, ClusterEvent.EventType... eventTypes);
}