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/*
 * Copyright 2010-2011 Ning, Inc.
 *
 * Ning 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 com.ning.metrics.serialization.writer;

import org.joda.time.DateTime;
import org.joda.time.MutableDateTime;
import org.joda.time.ReadableDateTime;
import org.joda.time.ReadablePeriod;

import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.atomic.AtomicInteger;

public class EventRate
{
    private static final int MAX_EVENT_QUEUE_SIZE = 1000;

    private final BlockingDeque> queue = new LinkedBlockingDeque>();
    private int rate = 0;
    private final ReadablePeriod rateWindow;
    private final BlockingDeque dateTimeQueue = new LinkedBlockingDeque();

    public EventRate(ReadablePeriod rateWindow)
    {
        this.rateWindow = rateWindow;
    }

    public void increment()
    {
        dateTimeQueue.add(truncateToSecond(getNow()));

        if (dateTimeQueue.size() > MAX_EVENT_QUEUE_SIZE) {
            updateRate();
        }
    }

    public long getRate()
    {
        updateRate();

        return rate;
    }

    private synchronized void updateRate()
    {
        List eventList = new ArrayList();
        dateTimeQueue.drainTo(eventList);

        for (DateTime dateTime : eventList) {
            rate++;
            Map.Entry lastPair = queue.peekLast();

            if (lastPair != null && lastPair.getKey().equals(dateTime)) {
                lastPair.getValue().incrementAndGet();
            }
            else {
                queue.add(new AbstractMap.SimpleImmutableEntry(dateTime, new AtomicInteger(1)));
            }

        }

        DateTime now = getNow();

        while (!queue.isEmpty() && !queue.peekFirst().getKey().plus(rateWindow).isAfter(now)) {
            Map.Entry firstPair = queue.pollFirst();
            rate -= firstPair.getValue().get();
        }
    }

    public DateTime truncateToSecond(ReadableDateTime time)
    {
        MutableDateTime result = new MutableDateTime(time);
        result.setMillisOfSecond(0);
        return new DateTime(result);
    }

    //hook for unit testing
    protected DateTime getNow()
    {
        return new DateTime();
    }
}