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.metrics;
  
  import com.google.auto.value.AutoValue;
  import org.joda.time.Instant;
  
  /** The result of a {@link Gauge} metric. */
  @AutoValue
  public abstract class GaugeResult {
    public abstract long getValue();
  
    public abstract Instant getTimestamp();
  
    public static GaugeResult create(long value, Instant timestamp) {
      return new AutoValue_GaugeResult(value, timestamp);
    }
  
    public static GaugeResult empty() {
      return EmptyGaugeResult.INSTANCE;
    }
  
    /** Empty {@link GaugeResult}, representing no values reported. */
    public static class EmptyGaugeResult extends GaugeResult {
  
      private static final EmptyGaugeResult INSTANCE = new EmptyGaugeResult();
      private static final Instant EPOCH = new Instant(0);
  
      private EmptyGaugeResult() {}
  
      @Override
      public long getValue() {
        return -1L;
      }
  
      @Override
      public Instant getTimestamp() {
        return EPOCH;
      }
    }
  }
  