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.sdk.nexmark;
  
  import java.io.Serializable;
  import org.apache.beam.sdk.metrics.Counter;
  import org.apache.beam.sdk.metrics.Distribution;
  import org.apache.beam.sdk.metrics.Metrics;
  import org.apache.beam.sdk.nexmark.model.KnownSize;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.values.PCollection;
  
  /**
   * A monitor of elements with support for later retrieving their metrics.
   *
   * @param <T> Type of element we are monitoring.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class Monitor<T extends KnownSize> implements Serializable {
    private class MonitorDoFn extends DoFn<T, T> {
      final Counter elementCounter = Metrics.counter(name, prefix + ".elements");
      final Counter bytesCounter = Metrics.counter(name, prefix + ".bytes");
      final Distribution processingTime = Metrics.distribution(name, prefix + ".processingTime");
      final Distribution eventTimestamp = Metrics.distribution(name, prefix + ".eventTimestamp");
  
      @ProcessElement
      public void processElement(ProcessContext c) {
        elementCounter.inc();
        bytesCounter.inc(c.element().sizeInBytes());
        processingTime.update(System.currentTimeMillis());
        eventTimestamp.update(c.timestamp().getMillis());
        c.output(c.element());
      }
    }
  
    public final String name;
    public final String prefix;
    private final MonitorDoFn doFn;
    private final PTransform<PCollection<? extends T>, PCollection<T>> transform;
  
    public Monitor(String name, String prefix) {
      this.name = name;
      this.prefix = prefix;
      doFn = new MonitorDoFn();
      transform = ParDo.of(doFn);
    }
  
    public PTransform<PCollection<? extends T>, PCollection<T>> getTransform() {
      return transform;
    }
  }
  