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/*-
 * Copyright (C) 2011, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This file was distributed by Oracle as part of a version of Oracle NoSQL
 * Database made available at:
 *
 * http://www.oracle.com/technetwork/database/database-technologies/nosqldb/downloads/index.html
 *
 * Please see the LICENSE file included in the top-level directory of the
 * appropriate version of Oracle NoSQL Database for a copy of the license and
 * additional information.
 */

package oracle.kv.impl.util.sklogger;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

/**
 * A CustomGauge as one kind of {@link Metric} is useful when Gauge value is
 * not possible to directly instrument code, as it is not in your control, such
 * as gauge System memory value.
 *  * Usage example:
 * 
 * private static class TestCalculator implements GaugeCalculator {
 *     @Override
 *     public List getValuesList() {
 *         {@literal Map metrics = new HashMap<>(2);}
 *         metrics.put("free", Runtime.getRuntime().freeMemory());
 *         metrics.put("total", Runtime.getRuntime().maxMemory());
 *         return Arrays.asList(new GaugeResult(metrics));
 *     }
 * }
 * CustomGauge memory = new CustomGauge("memory", new TestCalculator());
 * memory.getValuesList();
 * 
 * 
 */
public class CustomGauge extends Metric {

    private final static List EMPTY_LABEL_VALUES = Arrays.asList();
    private final GaugeCalculator gaugeCalculator;

    /**
     * @param name is metric name that will be used when metric is registered
     * and/or processed.
     * @param gaugeCalculator is used to get the current gauge value map.
     */
    public CustomGauge(final String name,
                       GaugeCalculator gaugeCalculator) {

        super(name);
        this.gaugeCalculator = gaugeCalculator;
    }

    /**
     * Implement the interface to get current GaugeResult list.
     */
    public interface GaugeCalculator extends Metric.Element {

        /**
         * Get current GaugeResult list.
         */
        List getValuesList();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected GaugeCalculator newElement() {
        return gaugeCalculator;
    }

    // Convenience methods.

    /**
     * {@link GaugeCalculator#getValuesList}.
     */
    public List getValuesList() {
        try {
            return gaugeCalculator.getValuesList();
        } catch (Exception e) {
        }
        return null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public MetricFamilySamples collect() {
        List gaugeResultList = null;
        try {
            gaugeResultList = gaugeCalculator.getValuesList();
        } catch (Exception e) {
        }
        if (gaugeResultList == null) {
            return null;
        }
        final List> samples =
            new ArrayList>(
                gaugeResultList.size());
        for (GaugeResult e : gaugeResultList) {
            samples.add(
                new MetricFamilySamples.Sample(
                    EMPTY_LABEL_VALUES, e));
        }
        return new MetricFamilySamples(statsName,
                                                    Type.CUSTOM_GAUGE,
                                                    labelNames, samples);
    }

    /**
     * Saving collected {@link CustomGauge} result.
     */
    public static class GaugeResult extends Metric.Result {

        private static final long serialVersionUID = 1L;

        private Map map;

        public GaugeResult(Map map) {
            this.map = map;
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public Map toMap() {
            return map;
        }
    }
}