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/**
 * Copyright (C) 2015 Red Hat, Inc.
 *
 * Licensed 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 io.fabric8.kubernetes.client.informers;

import io.fabric8.kubernetes.client.informers.cache.Store;

/**
 * SharedInformer defines basic methods of an informer.
 *
 * This has been ported from official go client: https://github.com/kubernetes/client-go/blob/master/tools/cache/shared_informer.go
 */
public interface SharedInformer extends AutoCloseable {

  /**
   * Add event handler
   *
   * @param handler event handler
   */
  void addEventHandler(ResourceEventHandler handler);

  /**
   * Adds an event handler to the shared informer using the specified resync period.
   * Events to a single handler are delivered sequentially, but there is no
   * coordination between different handlers.
   *
   * @param handle the event handler
   * @param resyncPeriod the specific resync period
   */
  void addEventHandlerWithResyncPeriod(ResourceEventHandler handle, long resyncPeriod);

  /**
   * Starts the shared informer, which will be stopped when {@link #stop()} is called.
   * 
   * 
Only one start attempt is made - subsequent calls will not re-start the informer.
   * 
   * 
If the informer is not already running, this is a blocking call
   */
  void run();

  /**
   * Stops the shared informer.  The informer cannot be started again.
   */
  void stop();
  
  @Override
  default void close() {
    stop();
  }

  /**
   * Return true if the informer has ever synced
   */
  default boolean hasSynced() {
    return lastSyncResourceVersion() != null;
  }

  /**
   * The resource version observed when last synced with the underlying store.
   * The value returned is not synchronized with access to the underlying store
   * and is not thread-safe.
   *
   * @return string value or null if never synced
   */
  String lastSyncResourceVersion();
  
  /**
   * Return true if the informer is running
   */
  boolean isRunning();

  /**
   * Return the class this informer is watching
   */
  Class getApiTypeClass();
  
  /**
   * Return true if the informer is actively watching
   * 
Will return false when {@link #isRunning()} is true when the watch needs to be re-established.
   */
  boolean isWatching();
  
  /**
   * Return the Store associated with this informer
   * @return the store
   */
  Store getStore();
}