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 static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  
  import java.util.Arrays;
  import java.util.List;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Joiner;
  import org.joda.time.Instant;
  
  /**
   * A composite {@link Trigger} that executes its sub-triggers in order. Only one sub-trigger is
   * executing at a time, and any time it fires the {@code AfterEach} fires. When the currently
   * executing sub-trigger finishes, the {@code AfterEach} starts executing the next sub-trigger.
   *
   * <p>{@code AfterEach.inOrder(t1, t2, ...)} finishes when all of the sub-triggers have finished.
   *
   * <p>The following properties hold:
   *
   * <ul>
   *   <li>{@code AfterEach.inOrder(AfterEach.inOrder(a, b), c)} behaves the same as {@code
   *       AfterEach.inOrder(a, b, c)} and {@code AfterEach.inOrder(a, AfterEach.inOrder(b, c)}.
   *   <li>{@code AfterEach.inOrder(Repeatedly.forever(a), b)} behaves the same as {@code
   *       Repeatedly.forever(a)}, since the repeated trigger never finishes.
   * </ul>
   */
  public class AfterEach extends Trigger {
  
    private AfterEach(List<Trigger> subTriggers) {
      super(subTriggers);
      checkArgument(subTriggers.size() > 1);
    }
  
    /** Returns an {@code AfterEach} {@code Trigger} with the given subtriggers. */
    @SafeVarargs
    public static AfterEach inOrder(Trigger... triggers) {
      return new AfterEach(Arrays.asList(triggers));
    }
  
    /** Returns an {@code AfterEach} {@code Trigger} with the given subtriggers. */
    public static AfterEach inOrder(List<Trigger> triggers) {
      return new AfterEach(triggers);
    }
  
    @Override
    public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
      // This trigger will fire at least once when the first trigger in the sequence
      // fires at least once.
      return subTriggers.get(0).getWatermarkThatGuaranteesFiring(window);
    }
  
    @Override
    public boolean mayFinish() {
      return subTriggers.stream().allMatch(trigger -> trigger.mayFinish());
    }
  
    @Override
    protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
      return Repeatedly.forever(new AfterFirst(continuationTriggers));
    }
  
    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder("AfterEach.inOrder(");
      Joiner.on(", ").appendTo(builder, subTriggers);
      builder.append(")");
  
      return builder.toString();
    }
  }
  