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The official Couchbase JVM Core IO Library
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/**
 * Written by Gil Tene of Azul Systems, and released to the public domain,
 * as explained at http://creativecommons.org/publicdomain/zero/1.0/
 *
 * @author Gil Tene
 */

package com.couchbase.client.core.deps.org.HdrHistogram;

import java.util.Iterator;

/**
 * Used for iterating through histogram values according to percentile levels. The iteration is
 * performed in steps that start at 0% and reduce their distance to 100% according to the
 * percentileTicksPerHalfDistance parameter, ultimately reaching 100% when all recorded histogram
 * values are exhausted.
*/
public class PercentileIterator extends AbstractHistogramIterator implements Iterator {
    int percentileTicksPerHalfDistance;
    double percentileLevelToIterateTo;
    double percentileLevelToIterateFrom;
    boolean reachedLastRecordedValue;

    /**
     * Reset iterator for re-use in a fresh iteration over the same histogram data set.
     *
     * @param percentileTicksPerHalfDistance The number of iteration steps per half-distance to 100%.
     */
    public void reset(final int percentileTicksPerHalfDistance) {
        reset(histogram, percentileTicksPerHalfDistance);
    }

    private void reset(final AbstractHistogram histogram, final int percentileTicksPerHalfDistance) {
        super.resetIterator(histogram);
        this.percentileTicksPerHalfDistance = percentileTicksPerHalfDistance;
        this.percentileLevelToIterateTo = 0.0;
        this.percentileLevelToIterateFrom = 0.0;
        this.reachedLastRecordedValue = false;
    }

    /**
     * @param histogram The histogram this iterator will operate on
     * @param percentileTicksPerHalfDistance The number of iteration steps per half-distance to 100%.
     */
    public PercentileIterator(final AbstractHistogram histogram, final int percentileTicksPerHalfDistance) {
        reset(histogram, percentileTicksPerHalfDistance);
    }

    @Override
    public boolean hasNext() {
        if (super.hasNext())
            return true;
        // We want one additional last step to 100%
        if (!reachedLastRecordedValue && (arrayTotalCount > 0)) {
            percentileLevelToIterateTo = 100.0;
            reachedLastRecordedValue = true;
            return true;
        }
        return false;
    }

    @Override
    void incrementIterationLevel() {
        percentileLevelToIterateFrom = percentileLevelToIterateTo;
        long percentileReportingTicks =
                percentileTicksPerHalfDistance *
                        (long) Math.pow(2,
                                (long) (Math.log(100.0 / (100.0 - (percentileLevelToIterateTo))) / Math.log(2)) + 1);
        percentileLevelToIterateTo += 100.0 / percentileReportingTicks;
    }

    @Override
    boolean reachedIterationLevel() {
        if (countAtThisValue == 0)
            return false;
        double currentPercentile = (100.0 * (double) totalCountToCurrentIndex) / arrayTotalCount;
        return (currentPercentile >= percentileLevelToIterateTo);
    }

    @Override
    double getPercentileIteratedTo() {
        return percentileLevelToIterateTo;
    }

    @Override
    double getPercentileIteratedFrom() {
        return percentileLevelToIterateFrom;
    }
}