code: /*
   * 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.skywalking.oap.server.telemetry.prometheus;
  
  import io.prometheus.client.Histogram;
  import org.apache.skywalking.oap.server.telemetry.api.HistogramMetrics;
  import org.apache.skywalking.oap.server.telemetry.api.MetricsTag;
  
  /**
   * HistogramMetrics metrics in Prometheus implementor.
   */
  public class PrometheusHistogramMetrics extends HistogramMetrics {
      private InnerMetricObject inner;
      private final double[] buckets;
  
      public PrometheusHistogramMetrics(String name, String tips, MetricsTag.Keys labels, MetricsTag.Values values,
          double... buckets) {
          inner = new InnerMetricObject(name, tips, labels, values);
          this.buckets = buckets;
      }
  
      @Override
      public void observe(double value) {
          Histogram.Child metrics = inner.getMetric();
          if (metrics != null) {
              metrics.observe(value);
          }
      }
  
      class InnerMetricObject extends BaseMetrics<Histogram, Histogram.Child> {
          public InnerMetricObject(String name, String tips, MetricsTag.Keys labels, MetricsTag.Values values) {
              super(name, tips, labels, values);
          }
  
          @Override
          protected Histogram create(String[] labelNames) {
              Histogram.Builder builder = Histogram.build().name(name).help(tips);
              if (builder != null && buckets.length > 0) {
                  builder = builder.buckets(buckets);
              }
              return builder.labelNames(labelNames).register();
          }
      }
  }
  