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.transforms.windowing;
  
  import java.util.Arrays;
  import java.util.List;
  import org.joda.time.Instant;
  
  /**
   * A {@link Trigger} that fires according to its subtrigger forever.
   *
   * <p>For example, to fire after the end of the window, and every time late data arrives:
   *
   * <pre>{@code
   * Repeatedly.forever(AfterWatermark.pastEndOfWindow());
   * }</pre>
   *
   * <p>{@code Repeatedly.forever(someTrigger)} behaves like an infinite {@code
   * AfterEach.inOrder(someTrigger, someTrigger, someTrigger, ...)}.
   *
   * <p>You can use {@link #orFinally(OnceTrigger)} to let another trigger interrupt the repetition.
   */
  public class Repeatedly extends Trigger {
  
    private static final int REPEATED = 0;
  
    /**
     * Create a composite trigger that repeatedly executes the trigger {@code repeated}, firing each
     * time it fires and ignoring any indications to finish.
     *
     * <p>Unless used with {@link Trigger#orFinally} the composite trigger will never finish.
     *
     * @param repeated the trigger to execute repeatedly.
     */
    public static Repeatedly forever(Trigger repeated) {
      return new Repeatedly(repeated);
    }
  
    private Trigger repeatedTrigger;
  
    private Repeatedly(Trigger repeatedTrigger) {
      super(Arrays.asList(repeatedTrigger));
      this.repeatedTrigger = repeatedTrigger;
    }
  
    public Trigger getRepeatedTrigger() {
      return repeatedTrigger;
    }
  
    @Override
    public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
      // This trigger fires once the repeated trigger fires.
      return subTriggers.get(REPEATED).getWatermarkThatGuaranteesFiring(window);
    }
  
    @Override
    public boolean mayFinish() {
      return false;
    }
  
    @Override
    protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
      return new Repeatedly(continuationTriggers.get(REPEATED));
    }
  
    @Override
    public String toString() {
      return String.format("Repeatedly.forever(%s)", subTriggers.get(REPEATED));
    }
  }
  