/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.internal.batchimport.staging;

import static java.lang.Math.min;

import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicLongArray;

/**
 * In a moving average calculation, only the last N values are considered.
 */
public class MovingAverage {
    private final AtomicLongArray values;
    private final AtomicLong total = new AtomicLong();
    private final AtomicLong valueCursor = new AtomicLong();

    MovingAverage(int numberOfTrackedValues) {
        this.values = new AtomicLongArray(numberOfTrackedValues);
    }

    public void add(long value) {
        long cursor = valueCursor.getAndIncrement();
        long prevValue = values.getAndSet((int) (cursor % values.length()), value);
        total.addAndGet(value - prevValue);
    }

    private int numberOfCurrentlyTrackedValues() {
        return (int) min(valueCursor.get(), values.length());
    }

    public long total() {
        return total.get();
    }

    public long average() {
        int trackedValues = numberOfCurrentlyTrackedValues();
        return trackedValues > 0 ? total.get() / trackedValues : 0;
    }

    public void reset() {
        for (int i = 0; i < values.length(); i++) {
            values.set(i, 0);
        }
        total.set(0);
        valueCursor.set(0);
    }
}
