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.testing;
  
  import org.apache.beam.sdk.transforms.GroupByKey;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.Reify;
  import org.apache.beam.sdk.transforms.Values;
  import org.apache.beam.sdk.transforms.WithKeys;
  import org.apache.beam.sdk.transforms.windowing.Never;
  import org.apache.beam.sdk.transforms.windowing.Window;
  import org.apache.beam.sdk.transforms.windowing.WindowFn;
  import org.apache.beam.sdk.util.IdentityWindowFn;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.TypeDescriptor;
  import org.apache.beam.sdk.values.ValueInSingleWindow;
  
  /**
   * Gathers all panes of each window into exactly one output.
   *
   * <p>Note that this will delay the output of a window until the garbage collection time (when the
   * watermark passes the end of the window plus allowed lateness) even if the upstream triggers
   * closed the window earlier.
   */
  class GatherAllPanes<T>
      extends PTransform<PCollection<T>, PCollection<Iterable<ValueInSingleWindow<T>>>> {
    /**
     * Gathers all panes of each window into a single output element.
     *
     * <p>This will gather all output panes into a single element, which causes them to be colocated
     * on a single worker. As a result, this is only suitable for {@link PCollection PCollections}
     * where all of the output elements for each pane fit in memory, such as in tests.
     */
    public static <T> GatherAllPanes<T> globally() {
      return new GatherAllPanes<>();
    }
  
    private GatherAllPanes() {}
  
    @Override
    public PCollection<Iterable<ValueInSingleWindow<T>>> expand(PCollection<T> input) {
      WindowFn<?, ?> originalWindowFn = input.getWindowingStrategy().getWindowFn();
  
      return input
          .apply(Reify.windows())
          .apply(
              WithKeys.<Integer, ValueInSingleWindow<T>>of(0)
                  .withKeyType(new TypeDescriptor<Integer>() {}))
          .apply(
              Window.into(
                      new IdentityWindowFn<KV<Integer, ValueInSingleWindow<T>>>(
                          originalWindowFn.windowCoder()))
                  .triggering(Never.ever())
                  .withAllowedLateness(input.getWindowingStrategy().getAllowedLateness())
                  .discardingFiredPanes())
          // all values have the same key so they all appear as a single output element
          .apply(GroupByKey.create())
          .apply(Values.create())
          .setWindowingStrategyInternal(input.getWindowingStrategy());
    }
  }
  