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.dataflow;
  
  import java.util.ArrayList;
  import java.util.List;
  import org.apache.beam.runners.dataflow.DataflowRunner.StreamingPCollectionViewWriterFn;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.coders.CoderRegistry;
  import org.apache.beam.sdk.coders.ListCoder;
  import org.apache.beam.sdk.runners.AppliedPTransform;
  import org.apache.beam.sdk.transforms.Combine;
  import org.apache.beam.sdk.transforms.Combine.CombineFn;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.transforms.View.CreatePCollectionView;
  import org.apache.beam.sdk.util.construction.PTransformReplacements;
  import org.apache.beam.sdk.util.construction.SingleInputOutputOverrideFactory;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.apache.beam.sdk.values.PCollectionViews;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Lists;
  
  /**
   * Dataflow streaming overrides for {@link CreatePCollectionView}, specialized for different view
   * types.
   */
  class StreamingViewOverrides {
    static class StreamingCreatePCollectionViewFactory<ElemT, ViewT>
        extends SingleInputOutputOverrideFactory<
            PCollection<ElemT>, PCollection<ElemT>, CreatePCollectionView<ElemT, ViewT>> {
      @Override
      public PTransformReplacement<PCollection<ElemT>, PCollection<ElemT>> getReplacementTransform(
          AppliedPTransform<
                  PCollection<ElemT>, PCollection<ElemT>, CreatePCollectionView<ElemT, ViewT>>
              transform) {
        StreamingCreatePCollectionView<ElemT, ViewT> streamingView =
            new StreamingCreatePCollectionView<>(transform.getTransform().getView());
        return PTransformReplacement.of(
            PTransformReplacements.getSingletonMainInput(transform), streamingView);
      }
  
      private static class StreamingCreatePCollectionView<ElemT, ViewT>
          extends PTransform<PCollection<ElemT>, PCollection<ElemT>> {
        private final PCollectionView<ViewT> view;
  
        private StreamingCreatePCollectionView(PCollectionView<ViewT> view) {
          this.view = view;
        }
  
        @Override
        public PCollection<ElemT> expand(PCollection<ElemT> input) {
          PCollection<List<ElemT>> elements;
          if (view.getViewFn() instanceof PCollectionViews.IsSingletonView) {
            elements =
                input.apply(
                    ParDo.of(
                        new DoFn<ElemT, List<ElemT>>() {
                          @DoFn.ProcessElement
                          public void process(@Element ElemT elemT, OutputReceiver<List<ElemT>> o) {
                            List<ElemT> elements = Lists.newArrayListWithExpectedSize(1);
                            elements.add(elemT);
                            o.output(elements);
                          }
                        }));
          } else {
            elements = input.apply(Combine.globally(new Concatenate<ElemT>()).withoutDefaults());
          }
          return elements
              .apply(ParDo.of(StreamingPCollectionViewWriterFn.create(view, input.getCoder())))
              .apply(CreateDataflowView.forStreaming(view));
        }
      }
    }
  
    /**
     * Combiner that combines {@code T}s into a single {@code List<T>} containing all inputs.
     *
     * @param <T> the type of elements to concatenate.
     */
    private static class Concatenate<T> extends CombineFn<T, List<T>, List<T>> {
      @Override
      public List<T> createAccumulator() {
        return new ArrayList<>();
      }
  
      @Override
      public List<T> addInput(List<T> accumulator, T input) {
        accumulator.add(input);
        return accumulator;
      }
  
      @Override
      public List<T> mergeAccumulators(Iterable<List<T>> accumulators) {
        List<T> result = createAccumulator();
        for (List<T> accumulator : accumulators) {
          result.addAll(accumulator);
        }
        return result;
      }
  
      @Override
      public List<T> extractOutput(List<T> accumulator) {
        return accumulator;
      }
  
      @Override
      public Coder<List<T>> getAccumulatorCoder(CoderRegistry registry, Coder<T> inputCoder) {
        return ListCoder.of(inputCoder);
      }
  
      @Override
      public Coder<List<T>> getDefaultOutputCoder(CoderRegistry registry, Coder<T> inputCoder) {
        return ListCoder.of(inputCoder);
      }
    }
  }
  