content: /**
   * 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.storm.starter.tools;
  
  import org.apache.commons.collections.buffer.CircularFifoBuffer;
  
  import backtype.storm.utils.Time;
  
  /**
   * This class tracks the time-since-last-modify of a "thing" in a rolling
   * fashion.
   * <p/>
   * For example, create a 5-slot tracker to track the five most recent
   * time-since-last-modify.
   * <p/>
   * You must manually "mark" that the "something" that you want to track -- in
   * terms of modification times -- has just been modified.
   */
  public class NthLastModifiedTimeTracker {
      
      private static final int MILLIS_IN_SEC = 1000;
      
      private final CircularFifoBuffer lastModifiedTimesMillis;
      
      public NthLastModifiedTimeTracker(int numTimesToTrack) {
          if (numTimesToTrack < 1) {
              throw new IllegalArgumentException(
                      "numTimesToTrack must be greater than zero (you requested " + numTimesToTrack + ")");
          }
          lastModifiedTimesMillis = new CircularFifoBuffer(numTimesToTrack);
          initLastModifiedTimesMillis();
      }
      
      private void initLastModifiedTimesMillis() {
          long nowCached = now();
          for (int i = 0; i < lastModifiedTimesMillis.maxSize(); i++) {
              lastModifiedTimesMillis.add(Long.valueOf(nowCached));
          }
      }
      
      private long now() {
          return Time.currentTimeMillis();
      }
      
      public int secondsSinceOldestModification() {
          long modifiedTimeMillis = ((Long) lastModifiedTimesMillis.get()).longValue();
          return (int) ((now() - modifiedTimeMillis) / MILLIS_IN_SEC);
      }
      
      public void markAsModified() {
          updateLastModifiedTime();
      }
      
      private void updateLastModifiedTime() {
          lastModifiedTimesMillis.add(now());
      }
      
  }
  