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 * 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
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package fish.payara.microprofile.metrics.cdi;

import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;

import java.util.stream.Stream;
import org.eclipse.microprofile.config.Config;
import org.eclipse.microprofile.config.ConfigProvider;
import org.eclipse.microprofile.metrics.Counter;
import org.eclipse.microprofile.metrics.Gauge;
import org.eclipse.microprofile.metrics.Histogram;
import org.eclipse.microprofile.metrics.Metadata;
import org.eclipse.microprofile.metrics.Metric;
import org.eclipse.microprofile.metrics.MetricID;
import org.eclipse.microprofile.metrics.MetricRegistry;
import org.eclipse.microprofile.metrics.Tag;
import org.eclipse.microprofile.metrics.Timer;

/**
 * Unfortunately the {@link MetricRegistry} has no generic versions of the get or register methods for the different
 * types of {@link Metric}s. Therefore this utility provides a generic API by mapping the generic methods to the type
 * specific ones.
 *
 * @author Jan Bernitt
 * @since 5.202
 */
public final class MetricUtils {

    @FunctionalInterface
    private interface By {

        R apply(MetricRegistry registry, A a, B b);
    }

    @FunctionalInterface
    private interface ByJust {

        R apply(MetricRegistry registry, A a);
    }

    private static final Map, MetricUtils> TYPES = new HashMap<>();

    public static final String TAG_METRIC_MP_SCOPE_NAME = "mp_scope";

    public static final String TAG_METRIC_MP_APP_NAME = "mp_app";
    
    public static final String METRIC_TAGS_GLOBAL_PROPERTY = "mp.metrics.tags";

    private final ByJust byName;
    private final By byNameAndTags;
    private final By byMetadataAndTags;

    private MetricUtils(
            ByJust byName,
            By byNameAndTags,
            By byMetadataAndTags) {
        this.byName = byName;
        this.byNameAndTags = byNameAndTags;
        this.byMetadataAndTags = byMetadataAndTags;
    }

    static  void register(
            Class type, ByJust byName,
            By byNameAndTags,
            By byMetadataAndTags) {
        TYPES.put(type, new MetricUtils<>(byName, byNameAndTags, byMetadataAndTags));
    }

    static {
        register(Counter.class, MetricRegistry::counter, MetricRegistry::counter, MetricRegistry::counter);
        register(Histogram.class, MetricRegistry::histogram, MetricRegistry::histogram, MetricRegistry::histogram);
        register(Timer.class, MetricRegistry::timer, MetricRegistry::timer, MetricRegistry::timer);
        register(Gauge.class, MetricUtils::getGauge, MetricUtils::getGauge, MetricUtils::getGauge);
    }

    @SuppressWarnings("unchecked")
    public static  T getOrRegisterByName(MetricRegistry registry, Class metric, String name) {
        return (T) getOrRegister(metric).byName.apply(registry, name);
    }

    @SuppressWarnings("unchecked")
    public static  T getOrRegisterByNameAndTags(MetricRegistry registry, Class metric, String name,
            Tag... tags) {
        return (T) getOrRegister(metric).byNameAndTags.apply(registry, name, tags);
    }

    @SuppressWarnings("unchecked")
    public static  T getOrRegisterByMetadataAndTags(MetricRegistry registry, Class metric,
            Metadata metadata, Tag... tags) {
        return (T) getOrRegister(metric).byMetadataAndTags.apply(registry, metadata, tags);
    }

    /**
     * This method will add the mp_scope to indicate scope of the metric if not available
     * @param scope the scope associated with the metric
     * @param tags current tags available for the metric
     * @return array of tags including the mp_scope tag
     */
    public static Tag[] setScopeTagForMetric(String scope, Tag... tags) {
        Tag[] tArray = new Tag[1];
        if(scope.equals(MetricRegistry.BASE_SCOPE)) {
            Tag t = new Tag("mp_scope", MetricRegistry.BASE_SCOPE);
            tArray[0] = t;
        } else if(scope.equals(MetricRegistry.VENDOR_SCOPE)) {
            Tag t = new Tag("mp_scope", MetricRegistry.VENDOR_SCOPE);
            tArray[0] = t;
        } else if(scope.equals(MetricRegistry.APPLICATION_SCOPE)) {
            Tag t = new Tag("mp_scope", MetricRegistry.APPLICATION_SCOPE);
            tArray[0] = t;
        } else if(scope != null) {
            Tag t = new Tag("mp_scope", scope);
            tArray[0] = t;
        }
        Tag[] mergeArray = Stream.concat(Arrays.stream(tags),
                        Arrays.stream(tArray)).
                toArray(v -> (Tag[]) Array.newInstance(tags.getClass().getComponentType(), v));
        return mergeArray;
    }

    private static  MetricUtils getOrRegister(Class metric) {
        MetricUtils getOrRegister = TYPES.get(metric);
        if (getOrRegister == null) {
            throw new IllegalArgumentException("Cannot get or register metrics of type " + metric);
        }
        return getOrRegister;
    }

    /*
     * Gauges can only be resolved as registering requires the actual gauge instance.
     */

    private static Gauge getGauge(MetricRegistry registry, String name) {
        return getGauge(registry, name, new Tag[0]);
    }

    private static Gauge getGauge(MetricRegistry registry, Metadata metadata, Tag[] tags) {
        return getGauge(registry, metadata.getName(), tags);
    }

    @SuppressWarnings("unchecked")
    private static Gauge getGauge(MetricRegistry registry, String name, Tag[] tags) {
        MetricID complementedMetricID = new MetricID(name, tags);
        Gauge gauge = registry.getGauges().get(complementedMetricID);
        return gauge != null ? gauge : new LazyGauge<>(() -> registry.getGauges().get(complementedMetricID));
    }

    public static Tag[] resolveGlobalTagsConfiguration() {
        Config config = MetricUtils.getConfigProvider();
        if (config != null) {
            Optional globalTags = config.getOptionalValue(METRIC_TAGS_GLOBAL_PROPERTY, String.class);
            if (globalTags.isPresent()) {
                return parseGlobalTags(globalTags.get());
            } else {
                return new Tag[0];
            }
        } else {
            return new Tag[0];
        }
    }

    private static Tag[] parseGlobalTags(String globalTags) {
        if (globalTags == null || globalTags.length() == 0) {
            return new Tag[0];
        }

        String[] keyValuePairs = globalTags.split("(? implements Gauge {

        private final AtomicReference> gauge = new AtomicReference<>();
        private final Supplier> lookup;
        LazyGauge(Supplier> lookup) {
            this.lookup = lookup;
        }
        @Override
        public T getValue() {
            Gauge lazy = gauge.updateAndGet(instance -> instance != null ? instance : lookup.get());
            return lazy == null ? null : lazy.getValue();
        }
    }

    public static Config getConfigProvider() {
        try {
            return ConfigProvider.getConfig();
        } catch(Exception e) {
            return null;
        }
    }

}