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/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * 
 *    Copyright (c) [2018] Payara Foundation and/or its affiliates. All rights reserved.
 * 
 *     The contents of this file are subject to the terms of either the GNU
 *     General Public License Version 2 only ("GPL") or the Common Development
 *     and Distribution License("CDDL") (collectively, the "License").  You
 *     may not use this file except in compliance with the License.  You can
 *     obtain a copy of the License at
 *     https://github.com/payara/Payara/blob/master/LICENSE.txt
 *     See the License for the specific
 *     language governing permissions and limitations under the License.
 * 
 *     When distributing the software, include this License Header Notice in each
 *     file and include the License file at glassfish/legal/LICENSE.txt.
 * 
 *     GPL Classpath Exception:
 *     The Payara Foundation designates this particular file as subject to the "Classpath"
 *     exception as provided by the Payara Foundation in the GPL Version 2 section of the License
 *     file that accompanied this code.
 * 
 *     Modifications:
 *     If applicable, add the following below the License Header, with the fields
 *     enclosed by brackets [] replaced by your own identifying information:
 *     "Portions Copyright [year] [name of copyright owner]"
 * 
 *     Contributor(s):
 *     If you wish your version of this file to be governed by only the CDDL or
 *     only the GPL Version 2, indicate your decision by adding "[Contributor]
 *     elects to include this software in this distribution under the [CDDL or GPL
 *     Version 2] license."  If you don't indicate a single choice of license, a
 *     recipient has the option to distribute your version of this file under
 *     either the CDDL, the GPL Version 2 or to extend the choice of license to
 *     its licensees as provided above.  However, if you add GPL Version 2 code
 *     and therefore, elected the GPL Version 2 license, then the option applies
 *     only if the new code is made subject to such option by the copyright
 *     holder.
 *
 * *****************************************************************************
 * Copyright 2010-2013 Coda Hale and Yammer, Inc.
 *
 * 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.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package fish.payara.microprofile.metrics.impl;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAdder;
import javax.enterprise.inject.Vetoed;
import org.eclipse.microprofile.metrics.Meter;

/**
 * A meter metric which measures mean throughput and one-, five-, and
 * fifteen-minute exponentially-weighted moving average throughputs.
 *
 * @see EWMA
 */
@Vetoed
public class MeterImpl implements Meter {

    private static final long TICK_INTERVAL = TimeUnit.SECONDS.toNanos(5);

    private final EWMA m1Rate = EWMA.oneMinuteEWMA();
    private final EWMA m5Rate = EWMA.fiveMinuteEWMA();
    private final EWMA m15Rate = EWMA.fifteenMinuteEWMA();

    private final LongAdder count = new LongAdder();
    private final long startTime;
    private final AtomicLong lastTick;
    private final Clock clock;

    /**
     * Creates a new {@link MeterImpl}.
     */
    public MeterImpl() {
        this(Clock.defaultClock());
    }

    /**
     * Creates a new {@link MeterImpl}.
     *
     * @param clock the clock to use for the meter ticks
     */
    public MeterImpl(Clock clock) {
        this.clock = clock;
        this.startTime = this.clock.getTick();
        this.lastTick = new AtomicLong(startTime);
    }

    /**
     * Mark the occurrence of an event.
     */
    @Override
    public void mark() {
        mark(1);
    }

    /**
     * Mark the occurrence of a given number of events.
     *
     * @param n the number of events
     */
    @Override
    public void mark(long n) {
        tickIfNecessary();
        count.add(n);
        m1Rate.update(n);
        m5Rate.update(n);
        m15Rate.update(n);
    }

    private void tickIfNecessary() {
        final long oldTick = lastTick.get();
        final long newTick = clock.getTick();
        final long age = newTick - oldTick;
        if (age > TICK_INTERVAL) {
            final long newIntervalStartTick = newTick - age % TICK_INTERVAL;
            if (lastTick.compareAndSet(oldTick, newIntervalStartTick)) {
                final long requiredTicks = age / TICK_INTERVAL;
                for (long i = 0; i < requiredTicks; i++) {
                    m1Rate.tick();
                    m5Rate.tick();
                    m15Rate.tick();
                }
            }
        }
    }

    @Override
    public long getCount() {
        return count.sum();
    }

    @Override
    public double getFifteenMinuteRate() {
        tickIfNecessary();
        return m15Rate.getRate(TimeUnit.SECONDS);
    }

    @Override
    public double getFiveMinuteRate() {
        tickIfNecessary();
        return m5Rate.getRate(TimeUnit.SECONDS);
    }

    @Override
    public double getMeanRate() {
        if (getCount() == 0) {
            return 0.0;
        } else {
            final double elapsed = clock.getTick() - startTime;
            return getCount() / elapsed * TimeUnit.SECONDS.toNanos(1);
        }
    }

    @Override
    public double getOneMinuteRate() {
        tickIfNecessary();
        return m1Rate.getRate(TimeUnit.SECONDS);
    }
}