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 com.alibaba.jstorm.window;
  
  import backtype.storm.task.TopologyContext;
  import java.util.Map;
  
  /**
   * Periodic watermark generator, used in WindowedBolt when upstream/source doesn't send watermarks.
   * Use code like following to register a watermark generator:
   * <pre>{@code
   *  BaseWindowedBolt windowedBolt = new YourBolt();
   *  windowedBolt.withWatermarkGenerator(new PeriodicWatermarkGenerator());
   * }
   * </pre>
   *
   * Note that periodic watermark generator might be quite inaccurate about real watermarks since it has no context
   * about data source. A better approach would be sending watermarks from spout manually, or track upstream watermarks
   * so that you have a big picture about the progress of upstream flow.
   *
   * @author Cody
   * @since 2.3.0
   */
  public class PeriodicWatermarkGenerator implements WatermarkGenerator {
  
      private static final long serialVersionUID = 1L;
  
      private long maxTimestamp = Long.MIN_VALUE;
      private long maxLagMs = 0L;
      private long watermarkInterval;
  
      public PeriodicWatermarkGenerator(Time maxLag, Time triggerPeriod) {
          this.maxLagMs = maxLag.toMilliseconds();
          this.watermarkInterval = triggerPeriod.toMilliseconds();
      }
  
      @Override
      public void init(Map conf, TopologyContext context) {
      }
  
      @Override
      public long getCurrentWatermark() {
          if (maxTimestamp < 0) {
              return 0L;
          }
          long ts = maxTimestamp - maxLagMs;
          if (ts < 0) {
              return 0L;
          }
          return ts;
      }
  
      @Override
      public void onElement(long timestamp) {
          if (timestamp > maxTimestamp) {
              this.maxTimestamp = timestamp;
          }
      }
  
      @Override
      public long getWatermarkInterval() {
          return this.watermarkInterval;
      }
  }