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.runners.core.triggers;
  
  import org.apache.beam.sdk.transforms.GroupByKey;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  
  /**
   * A {@link TriggerStateMachine} which never fires.
   *
   * <p>Using this trigger will only produce output when the watermark passes the end of the {@link
   * BoundedWindow window} plus the allowed lateness.
   */
  public final class NeverStateMachine extends TriggerStateMachine {
    /**
     * Returns a trigger which never fires. Output will be produced from the using {@link GroupByKey}
     * when the {@link BoundedWindow} closes.
     */
    public static NeverStateMachine ever() {
      // NeverTrigger ignores all inputs and is Window-type independent.
      return new NeverStateMachine();
    }
  
    private NeverStateMachine() {
      super(null);
    }
  
    @Override
    public void prefetchOnElement(PrefetchContext c) {}
  
    @Override
    public void onElement(OnElementContext c) {}
  
    @Override
    public void prefetchOnMerge(MergingPrefetchContext c) {}
  
    @Override
    public void onMerge(OnMergeContext c) {}
  
    @Override
    public void prefetchShouldFire(PrefetchContext c) {}
  
    @Override
    public boolean shouldFire(TriggerStateMachine.TriggerContext context) {
      return false;
    }
  
    @Override
    public void onFire(TriggerStateMachine.TriggerContext context) {
      throw new UnsupportedOperationException(
          String.format("%s should never fire", getClass().getSimpleName()));
    }
  }
  