/*
 * Copyright 2017 LinkedIn Corp. All rights reserved.
 *
 * 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.
 */
package com.github.ambry.clustermap;

import org.apache.helix.NotificationContext;
import org.apache.helix.model.Message;
import org.apache.helix.participant.statemachine.StateModel;
import org.apache.helix.participant.statemachine.StateModelInfo;
import org.apache.helix.participant.statemachine.StateModelParser;
import org.apache.helix.participant.statemachine.Transition;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * {@link StateModel} to use when the Ambry participants (datanodes) register to Helix. The methods are callbacks
 * that get called within a participant whenever its state changes in Helix. For now these are no-ops.
 *
 * In the critical path of puts and gets, there are no leader replicas in Ambry. Every replica can serve reads and
 * writes. However, going forward, it is useful to have one of the replicas chosen as a LEADER for purposes such as
 * replication.
 */
@StateModelInfo(initialState = "OFFLINE", states = {"LEADER", "STANDBY"})
public class AmbryStateModel extends StateModel {
  private Logger logger = LoggerFactory.getLogger(getClass());

  AmbryStateModel() {
    StateModelParser parser = new StateModelParser();
    _currentState = parser.getInitialState(AmbryStateModel.class);
  }

  @Transition(to = "STANDBY", from = "OFFLINE")
  public void onBecomeStandbyFromOffline(Message message, NotificationContext context) {
    logger.info("Becoming STANDBY from OFFLINE");
  }

  @Transition(to = "LEADER", from = "STANDBY")
  public void onBecomeLeaderFromStandby(Message message, NotificationContext context) {
    logger.info("Becoming LEADER from STANDBY");
  }

  @Transition(to = "STANDBY", from = "LEADER")
  public void onBecomeStandbyFromLeader(Message message, NotificationContext context) {
    logger.info("Becoming STANDBY from LEADER");
  }

  @Transition(to = "OFFLINE", from = "STANDBY")
  public void onBecomeOfflineFromStandby(Message message, NotificationContext context) {
    logger.info("Becoming OFFLINE from STANDBY");
  }

  @Transition(to = "OFFLINE", from = "LEADER")
  public void onBecomeOfflineFromLeader(Message message, NotificationContext context) {
    logger.info("Becoming OFFLINE from LEADER");
  }
}