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   * 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.flink;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.Map;
  import org.apache.beam.runners.core.Concatenate;
  import org.apache.beam.sdk.coders.ListCoder;
  import org.apache.beam.sdk.runners.AppliedPTransform;
  import org.apache.beam.sdk.runners.PTransformOverrideFactory;
  import org.apache.beam.sdk.transforms.Combine;
  import org.apache.beam.sdk.transforms.MapElements;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.util.Preconditions;
  import org.apache.beam.sdk.util.construction.CreatePCollectionViewTranslation;
  import org.apache.beam.sdk.util.construction.ReplacementOutputs;
  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.sdk.values.TupleTag;
  import org.apache.beam.sdk.values.TypeDescriptor;
  import org.apache.beam.sdk.values.TypeDescriptors;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Lists;
  
  /** Flink streaming overrides for various view (side input) transforms. */
  @SuppressWarnings({
    "rawtypes" // TODO(https://github.com/apache/beam/issues/20447)
  })
  class CreateStreamingFlinkView<ElemT, ViewT>
      extends PTransform<PCollection<ElemT>, PCollection<ElemT>> {
    private final PCollectionView<ViewT> view;
  
    public static final String CREATE_STREAMING_FLINK_VIEW_URN =
        "beam:transform:flink:create-streaming-flink-view:v1";
  
    public CreateStreamingFlinkView(PCollectionView<ViewT> view) {
      this.view = view;
    }
  
    @Override
    public PCollection<ElemT> expand(PCollection<ElemT> input) {
      PCollection<List<ElemT>> iterable;
      // See https://github.com/apache/beam/pull/25940
      if (view.getViewFn() instanceof PCollectionViews.IsSingletonView) {
        TypeDescriptor<ElemT> inputType = Preconditions.checkStateNotNull(input.getTypeDescriptor());
        iterable =
            input
                .apply(MapElements.into(TypeDescriptors.lists(inputType)).via(Lists::newArrayList))
                .setCoder(ListCoder.of(input.getCoder()));
      } else {
        iterable = input.apply(Combine.globally(new Concatenate<ElemT>()).withoutDefaults());
      }
  
      iterable.apply(CreateFlinkPCollectionView.of(view));
      return input;
    }
  
    /**
     * Creates a primitive {@link PCollectionView}.
     *
     * <p>For internal use only by runner implementors.
     *
     * @param <ElemT> The type of the elements of the input PCollection
     * @param <ViewT> The type associated with the {@link PCollectionView} used as a side input
     */
    public static class CreateFlinkPCollectionView<ElemT, ViewT>
        extends PTransform<PCollection<List<ElemT>>, PCollection<List<ElemT>>> {
      private PCollectionView<ViewT> view;
  
      private CreateFlinkPCollectionView(PCollectionView<ViewT> view) {
        this.view = view;
      }
  
      public static <ElemT, ViewT> CreateFlinkPCollectionView<ElemT, ViewT> of(
          PCollectionView<ViewT> view) {
        return new CreateFlinkPCollectionView<>(view);
      }
  
      @Override
      public PCollection<List<ElemT>> expand(PCollection<List<ElemT>> input) {
        return PCollection.createPrimitiveOutputInternal(
            input.getPipeline(), input.getWindowingStrategy(), input.isBounded(), input.getCoder());
      }
  
      public PCollectionView<ViewT> getView() {
        return view;
      }
    }
  
    public static class Factory<ElemT, ViewT>
        implements PTransformOverrideFactory<
            PCollection<ElemT>,
            PCollection<ElemT>,
            PTransform<PCollection<ElemT>, PCollection<ElemT>>> {
  
      static final Factory INSTANCE = new Factory();
  
      private Factory() {}
  
      @Override
      public PTransformReplacement<PCollection<ElemT>, PCollection<ElemT>> getReplacementTransform(
          AppliedPTransform<
                  PCollection<ElemT>,
                  PCollection<ElemT>,
                  PTransform<PCollection<ElemT>, PCollection<ElemT>>>
              transform) {
        PCollection<ElemT> collection =
            (PCollection<ElemT>) Iterables.getOnlyElement(transform.getInputs().values());
        PCollectionView<ViewT> view;
        try {
          view = CreatePCollectionViewTranslation.getView(transform);
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
        CreateStreamingFlinkView<ElemT, ViewT> createFlinkView = new CreateStreamingFlinkView<>(view);
        return PTransformReplacement.of(collection, createFlinkView);
      }
  
      @Override
      public Map<PCollection<?>, ReplacementOutput> mapOutputs(
          Map<TupleTag<?>, PCollection<?>> outputs, PCollection<ElemT> newOutput) {
        return ReplacementOutputs.singleton(outputs, newOutput);
      }
    }
  }
  