dnet-applications/libs/dnet-apps-common/src/main/java/eu/dnetlib/common/metrics/MetricUtils.java

package eu.dnetlib.common.metrics;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import javax.annotation.PostConstruct;

import org.apache.commons.lang3.StringUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import io.micrometer.core.instrument.Metrics;
import io.prometheus.client.Collector.MetricFamilySamples;
import io.prometheus.client.GaugeMetricFamily;
import io.prometheus.client.exporter.common.TextFormat;

@Component
public class MetricUtils {

	@Autowired(required = false)
	private Map<String, MetricInfo> kpiMetrics;

	private static final Log log = LogFactory.getLog(MetricUtils.class);

	@PostConstruct
	public void registerToMainEndpoint() {
		if (kpiMetrics != null) {
			kpiMetrics.forEach((k, v) -> Metrics.gauge(k, v, o -> o.obtainValue()));
			log.info("KPI METRICS REGISTERED: " + StringUtils.join(kpiMetrics.keySet(), ", "));
		}
	}

	public String output(final String contentType) {

		try {
			final List<MetricFamilySamples> samples = new ArrayList<>();
			if (kpiMetrics != null) {
				kpiMetrics.forEach((k, v) -> samples.add(new GaugeMetricFamily(k, "", v.obtainValue())));
			}
			final Writer writer = new StringWriter();
			TextFormat.writeFormat(contentType, writer, Collections.enumeration(samples));
			return writer.toString();
		} catch (final IOException e) {
			// This actually never happens since StringWriter::write() doesn't throw any IOException
			throw new RuntimeException("Writing metrics failed", e);
		}
	}

}