content: /*
   * 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.beam.runners.spark.structuredstreaming.metrics;
  
  import com.codahale.metrics.Gauge;
  import com.codahale.metrics.MetricFilter;
  import java.util.Map;
  import org.apache.beam.runners.spark.metrics.WithMetricsSupport;
  
  /**
   * {@link BeamMetricSet} is a {@link Gauge} that returns a map of multiple metrics which get
   * flattened in {@link WithMetricsSupport#getGauges()} for usage in {@link
   * org.apache.spark.metrics.sink.Sink Spark metric sinks}.
   *
   * <p>Note: Recent versions of Dropwizard {@link com.codahale.metrics.MetricRegistry MetricRegistry}
   * do not allow registering arbitrary implementations of {@link com.codahale.metrics.Metric Metrics}
   * and require usage of {@link Gauge} here.
   */
  // TODO: turn into MetricRegistry https://github.com/apache/beam/issues/22384
  abstract class BeamMetricSet implements Gauge<Map<String, Gauge<Double>>> {
  
    @Override
    public final Map<String, Gauge<Double>> getValue() {
      return getValue("", MetricFilter.ALL);
    }
  
    protected abstract Map<String, Gauge<Double>> getValue(String prefix, MetricFilter filter);
  
    protected Gauge<Double> staticGauge(Number number) {
      return new ConstantGauge(number.doubleValue());
    }
  
    private static class ConstantGauge implements Gauge<Double> {
      private final double value;
  
      ConstantGauge(double value) {
        this.value = value;
      }
  
      @Override
      public Double getValue() {
        return value;
      }
    }
  }
  