package eu.dnetlib.common.metrics;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.Set;

import io.micrometer.core.instrument.composite.CompositeMeterRegistry;
import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.Gauge;
import io.prometheus.client.exporter.common.TextFormat;

public class MetricUtils {

	private static final CompositeMeterRegistry meterRegistry = new CompositeMeterRegistry();
	private static final CollectorRegistry collectorRegistry = new CollectorRegistry(true);

	public static MetricInfo register(final String name, final MetricInfo metric) {
		final MetricInfo meter = meterRegistry.gauge(name, metric, MetricInfo::obtainValue);
		Gauge.build(name, name).register(collectorRegistry);
		return meter;
	}

	public static String output(final Set<String> metricsToInclude, final String contentType) {
		try {
			final Writer writer = new StringWriter();
			TextFormat.writeFormat(contentType, writer, collectorRegistry.filteredMetricFamilySamples(metricsToInclude));
			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);
		}
	}

}