/*
    * 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.hbase.regionserver.compactions;
  
  import java.util.Calendar;
  import java.util.GregorianCalendar;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
  
  @InterfaceAudience.Private
  public class CurrentHourProvider {
  
    private CurrentHourProvider() {
      throw new AssertionError();
    }
  
    private static final class Tick {
      final int currentHour;
      final long expirationTimeInMillis;
  
      Tick(int currentHour, long expirationTimeInMillis) {
        this.currentHour = currentHour;
        this.expirationTimeInMillis = expirationTimeInMillis;
      }
    }
  
    private static Tick nextTick() {
      Calendar calendar = new GregorianCalendar();
      calendar.setTimeInMillis(EnvironmentEdgeManager.currentTime());
      int currentHour = calendar.get(Calendar.HOUR_OF_DAY);
      moveToNextHour(calendar);
      return new Tick(currentHour, calendar.getTimeInMillis());
    }
  
    private static void moveToNextHour(Calendar calendar) {
      calendar.add(Calendar.HOUR_OF_DAY, 1);
      calendar.set(Calendar.MINUTE, 0);
      calendar.set(Calendar.SECOND, 0);
      calendar.set(Calendar.MILLISECOND, 0);
    }
  
    private static volatile Tick tick = nextTick();
  
    public static int getCurrentHour() {
      Tick tick = CurrentHourProvider.tick;
      if (EnvironmentEdgeManager.currentTime() < tick.expirationTimeInMillis) {
        return tick.currentHour;
      }
      tick = nextTick();
      CurrentHourProvider.tick = tick;
      return tick.currentHour;
    }
  
    //RestrictedApi - only to be called for tests
    static void advanceTick() {
      tick = nextTick();
    }
  }