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Jersey core server implementation
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/*
 * Copyright (c) 2015, 2019 Oracle and/or its affiliates. All rights reserved.
 * 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 org.glassfish.jersey.server.internal.monitoring.core;

import java.util.Arrays;
import java.util.Collection;
import java.util.concurrent.TimeUnit;

import static java.lang.Math.floor;

/**
 * A statistical snapshot of a {@link UniformTimeValuesSnapshot}.
 *
 * @author Stepan Vavra
 * @author Dropwizard Team
 * @see https://github.com/dropwizard/metrics
 */
public class UniformTimeValuesSnapshot extends AbstractTimeSnapshot {

    private final long[] values;

    /**
     * Create a new snapshot with the given values.
     *
     * @param values           an unordered set of values in the reservoir
     * @param timeInterval     The time interval this snapshot relates to
     * @param timeIntervalUnit The time unit of the time interval
     */
    public UniformTimeValuesSnapshot(Collection values, final long timeInterval, final TimeUnit timeIntervalUnit) {
        super(timeInterval, timeIntervalUnit);
        final Object[] copy = values.toArray();
        this.values = new long[copy.length];
        for (int i = 0; i < copy.length; i++) {
            this.values[i] = (Long) copy[i];
        }
        Arrays.sort(this.values);
    }

    /**
     * Returns the value at the given quantile.
     *
     * @param quantile a given quantile, in {@code [0..1]}
     * @return the value in the distribution at {@code quantile}
     */
    public double getValue(double quantile) {
        if (quantile < 0.0 || quantile > 1.0 || Double.isNaN(quantile)) {
            throw new IllegalArgumentException(quantile + " is not in [0..1] range");
        }

        if (values.length == 0) {
            return 0.0;
        }

        final double pos = quantile * (values.length + 1);
        final int index = (int) pos;

        if (index < 1) {
            return values[0];
        }

        if (index >= values.length) {
            return values[values.length - 1];
        }

        final double lower = values[index - 1];
        final double upper = values[index];
        return lower + (pos - floor(pos)) * (upper - lower);
    }

    /**
     * Returns the number of values in the snapshot.
     *
     * @return the number of values
     */
    @Override
    public long size() {
        return values.length;
    }

    /**
     * Returns the entire set of values in the snapshot.
     *
     * @return the entire set of values
     */
    public long[] getValues() {
        return Arrays.copyOf(values, values.length);
    }

    /**
     * Returns the highest value in the snapshot.
     *
     * @return the highest value
     */
    @Override
    public long getMax() {
        if (values.length == 0) {
            return 0;
        }
        return values[values.length - 1];
    }

    /**
     * Returns the lowest value in the snapshot.
     *
     * @return the lowest value
     */
    @Override
    public long getMin() {
        if (values.length == 0) {
            return 0;
        }
        return values[0];
    }

    /**
     * Returns the arithmetic mean of the values in the snapshot.
     *
     * @return the arithmetic mean
     */
    @Override
    public double getMean() {
        if (values.length == 0) {
            return 0;
        }

        double sum = 0;
        for (long value : values) {
            sum += value;
        }
        return sum / values.length;
    }
}