/**
* 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.hadoop.yarn.service;

import org.apache.hadoop.conf.Configuration;

/**
 * Service LifeCycle.
 */
public interface Service {

  /**
   * Service states
   */
  public enum STATE {
    /** Constructed but not initialized */
    NOTINITED,

    /** Initialized but not started or stopped */
    INITED,

    /** started and not stopped */
    STARTED,

    /** stopped. No further state transitions are permitted */
    STOPPED
  }

  /**
   * Initialize the service.
   *
   * The transition must be from {@link STATE#NOTINITED} to {@link STATE#INITED}
   * unless the operation failed and an exception was raised.
   * @param config the configuration of the service
   */
  void init(Configuration config);


  /**
   * Start the service.
   *
   * The transition should be from {@link STATE#INITED} to {@link STATE#STARTED}
   * unless the operation failed and an exception was raised.
   */

  void start();

  /**
   * Stop the service.
   *
   * This operation must be designed to complete regardless of the initial state
   * of the service, including the state of all its internal fields.
   */
  void stop();

  /**
   * Register an instance of the service state change events.
   * @param listener a new listener
   */
  void register(ServiceStateChangeListener listener);

  /**
   * Unregister a previously instance of the service state change events.
   * @param listener the listener to unregister.
   */
  void unregister(ServiceStateChangeListener listener);

  /**
   * Get the name of this service.
   * @return the service name
   */
  String getName();

  /**
   * Get the configuration of this service.
   * This is normally not a clone and may be manipulated, though there are no
   * guarantees as to what the consequences of such actions may be
   * @return the current configuration, unless a specific implentation chooses
   * otherwise.
   */
  Configuration getConfig();

  /**
   * Get the current service state
   * @return the state of the service
   */
  STATE getServiceState();

  /**
   * Get the service start time
   * @return the start time of the service. This will be zero if the service
   * has not yet been started.
   */
  long getStartTime();
}
