/**
 * 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());
    }
    
}