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Instrumentation of Java libraries using OpenTelemetry.
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/*
 * Copyright The OpenTelemetry Authors
 * SPDX-License-Identifier: Apache-2.0
 */

package io.opentelemetry.instrumentation.jmx.engine;

import static java.util.logging.Level.INFO;

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.common.Attributes;
import io.opentelemetry.api.common.AttributesBuilder;
import io.opentelemetry.api.metrics.DoubleGaugeBuilder;
import io.opentelemetry.api.metrics.LongCounterBuilder;
import io.opentelemetry.api.metrics.LongUpDownCounterBuilder;
import io.opentelemetry.api.metrics.Meter;
import io.opentelemetry.api.metrics.ObservableDoubleMeasurement;
import io.opentelemetry.api.metrics.ObservableLongMeasurement;
import java.util.Collection;
import java.util.function.Consumer;
import java.util.logging.Logger;
import javax.management.MBeanServer;
import javax.management.ObjectName;

/** A class responsible for maintaining the set of metrics to collect and report. */
class MetricRegistrar {

  private static final Logger logger = Logger.getLogger(MetricRegistrar.class.getName());

  private final Meter meter;

  MetricRegistrar(OpenTelemetry openTelemetry, String instrumentationScope) {
    meter = openTelemetry.getMeter(instrumentationScope);
  }

  /**
   * Accepts a MetricExtractor for registration and activation.
   *
   * @param server the MBeanServer to use to query for metric values
   * @param objectNames the Objectnames that are known to the server and that know the attribute
   *     that is required to get the metric values
   * @param extractor the MetricExtractor responsible for getting the metric values
   */
  void enrollExtractor(
      MBeanServer server,
      Collection objectNames,
      MetricExtractor extractor,
      AttributeInfo attributeInfo) {
    // For the first enrollment of the extractor we have to build the corresponding Instrument
    DetectionStatus status = new DetectionStatus(server, objectNames);
    boolean firstEnrollment;
    synchronized (extractor) {
      firstEnrollment = extractor.getStatus() == null;
      // For successive enrollments, it is sufficient to refresh the status
      extractor.setStatus(status);
    }

    if (firstEnrollment) {
      MetricInfo metricInfo = extractor.getInfo();
      String metricName = metricInfo.getMetricName();
      MetricInfo.Type instrumentType = metricInfo.getType();
      String description =
          metricInfo.getDescription() != null
              ? metricInfo.getDescription()
              : attributeInfo.getDescription();
      String unit = metricInfo.getUnit();

      switch (instrumentType) {
          // CHECKSTYLE:OFF
        case COUNTER:
          {
            // CHECKSTYLE:ON
            LongCounterBuilder builder = meter.counterBuilder(metricName);
            if (description != null) {
              builder = builder.setDescription(description);
            }
            if (unit != null) {
              builder = builder.setUnit(unit);
            }

            if (attributeInfo.usesDoubleValues()) {
              builder.ofDoubles().buildWithCallback(doubleTypeCallback(extractor));
            } else {
              builder.buildWithCallback(longTypeCallback(extractor));
            }
            logger.log(INFO, "Created Counter for {0}", metricName);
          }
          break;

          // CHECKSTYLE:OFF
        case UPDOWNCOUNTER:
          {
            // CHECKSTYLE:ON
            LongUpDownCounterBuilder builder = meter.upDownCounterBuilder(metricName);
            if (description != null) {
              builder = builder.setDescription(description);
            }
            if (unit != null) {
              builder = builder.setUnit(unit);
            }

            if (attributeInfo.usesDoubleValues()) {
              builder.ofDoubles().buildWithCallback(doubleTypeCallback(extractor));
            } else {
              builder.buildWithCallback(longTypeCallback(extractor));
            }
            logger.log(INFO, "Created UpDownCounter for {0}", metricName);
          }
          break;

          // CHECKSTYLE:OFF
        case GAUGE:
          {
            // CHECKSTYLE:ON
            DoubleGaugeBuilder builder = meter.gaugeBuilder(metricName);
            if (description != null) {
              builder = builder.setDescription(description);
            }
            if (unit != null) {
              builder = builder.setUnit(unit);
            }

            if (attributeInfo.usesDoubleValues()) {
              builder.buildWithCallback(doubleTypeCallback(extractor));
            } else {
              builder.ofLongs().buildWithCallback(longTypeCallback(extractor));
            }
            logger.log(INFO, "Created Gauge for {0}", metricName);
          }
      }
    }
  }

  /*
   * A method generating metric collection callback for asynchronous Measurement
   * of Double type.
   */
  static Consumer doubleTypeCallback(MetricExtractor extractor) {
    return measurement -> {
      DetectionStatus status = extractor.getStatus();
      if (status != null) {
        MBeanServer server = status.getServer();
        for (ObjectName objectName : status.getObjectNames()) {
          Number metricValue =
              extractor.getMetricValueExtractor().extractNumericalAttribute(server, objectName);
          if (metricValue != null) {
            // get the metric attributes
            Attributes attr = createMetricAttributes(server, objectName, extractor);
            measurement.record(metricValue.doubleValue(), attr);
          }
        }
      }
    };
  }

  /*
   * A method generating metric collection callback for asynchronous Measurement
   * of Long type.
   */
  static Consumer longTypeCallback(MetricExtractor extractor) {
    return measurement -> {
      DetectionStatus status = extractor.getStatus();
      if (status != null) {
        MBeanServer server = status.getServer();
        for (ObjectName objectName : status.getObjectNames()) {
          Number metricValue =
              extractor.getMetricValueExtractor().extractNumericalAttribute(server, objectName);
          if (metricValue != null) {
            // get the metric attributes
            Attributes attr = createMetricAttributes(server, objectName, extractor);
            measurement.record(metricValue.longValue(), attr);
          }
        }
      }
    };
  }

  /*
   * An auxiliary method for collecting measurement attributes to go along
   * the metric values
   */
  static Attributes createMetricAttributes(
      MBeanServer server, ObjectName objectName, MetricExtractor extractor) {
    MetricAttribute[] metricAttributes = extractor.getAttributes();
    AttributesBuilder attrBuilder = Attributes.builder();
    for (MetricAttribute metricAttribute : metricAttributes) {
      String attributeValue = metricAttribute.acquireAttributeValue(server, objectName);
      if (attributeValue != null) {
        attrBuilder = attrBuilder.put(metricAttribute.getAttributeName(), attributeValue);
      }
    }
    return attrBuilder.build();
  }
}