/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.pulsar.functions.instance.stats;

import io.prometheus.client.Collector;

import java.io.IOException;
import java.io.Writer;
import java.util.Enumeration;

/**
 * Provide Prometheus text format for a collection of metrics, without the HELP string
 */
public class PrometheusTextFormat {
    /**
     * Write out the text version 0.0.4 of the given MetricFamilySamples.
     */
    public static void write004(Writer writer, Enumeration<Collector.MetricFamilySamples> mfs) throws IOException {
        /*
         * See http://prometheus.io/docs/instrumenting/exposition_formats/ for the output format specification.
         */
        while (mfs.hasMoreElements()) {
            Collector.MetricFamilySamples metricFamilySamples = mfs.nextElement();
            for (Collector.MetricFamilySamples.Sample sample : metricFamilySamples.samples) {
                writer.write(sample.name);
                if (sample.labelNames.size() > 0) {
                    writer.write('{');
                    for (int i = 0; i < sample.labelNames.size(); ++i) {
                        writer.write(sample.labelNames.get(i));
                        writer.write("=\"");
                        writeEscapedLabelValue(writer, sample.labelValues.get(i));
                        writer.write("\",");
                    }
                    writer.write('}');
                }
                writer.write(' ');
                writer.write(Collector.doubleToGoString(sample.value));
                if (sample.timestampMs != null) {
                    writer.write(' ');
                    writer.write(sample.timestampMs.toString());
                }
                writer.write('\n');
            }
        }
    }

    private static void writeEscapedLabelValue(Writer writer, String s) throws IOException {
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch (c) {
            case '\\':
                writer.append("\\\\");
                break;
            case '\"':
                writer.append("\\\"");
                break;
            case '\n':
                writer.append("\\n");
                break;
            default:
                writer.append(c);
            }
        }
    }

}
