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;
  
  import org.apache.beam.sdk.annotations.Internal;
  import org.apache.beam.sdk.coders.ByteArrayCoder;
  import org.apache.beam.sdk.io.Read;
  import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
  import org.apache.beam.sdk.values.PBegin;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollection.IsBounded;
  import org.apache.beam.sdk.values.WindowingStrategy;
  
  /**
   * <b><i>For internal use only; no backwards-compatibility guarantees.</i></b>
   *
   * <p>A {@link PTransform} which produces a single empty byte array at the minimum timestamp in the
   * {@link GlobalWindow}.
   *
   * <p>Users should instead use {@link Create} or another {@link Read} transform to begin consuming
   * elements.
   */
  @Internal
  public class Impulse extends PTransform<PBegin, PCollection<byte[]>> {
    /** Create a new {@link Impulse} {@link PTransform}. */
    public static Impulse create() {
      return new Impulse();
    }
  
    private Impulse() {}
  
    @Override
    public PCollection<byte[]> expand(PBegin input) {
      return PCollection.createPrimitiveOutputInternal(
          input.getPipeline(),
          WindowingStrategy.globalDefault(),
          IsBounded.BOUNDED,
          ByteArrayCoder.of());
    }
  }
  