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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
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 * 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,
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 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.beam.runners.flink;

import com.google.common.collect.Iterables;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import org.apache.beam.runners.core.construction.ReplacementOutputs;
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.runners.PTransformOverrideFactory;
import org.apache.beam.sdk.transforms.Combine;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.View.CreatePCollectionView;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionView;
import org.apache.beam.sdk.values.PValue;
import org.apache.beam.sdk.values.TupleTag;

/** Flink streaming overrides for various view (side input) transforms. */
class CreateStreamingFlinkView
    extends PTransform, PCollection> {
  private final PCollectionView view;

  public static final String CREATE_STREAMING_FLINK_VIEW_URN =
      "beam:transform:flink:create-streaming-flink-view:v1";

  public CreateStreamingFlinkView(PCollectionView view) {
    this.view = view;
  }

  @Override
  public PCollection expand(PCollection input) {
    input
        .apply(Combine.globally(new Concatenate()).withoutDefaults())
        .apply(CreateFlinkPCollectionView.of(view));
    return input;
  }

  /**
   * Combiner that combines {@code T}s into a single {@code List} containing all inputs.
   *
   * For internal use by {@link CreateStreamingFlinkView}. This combiner requires that the input
   * {@link PCollection} fits in memory. For a large {@link PCollection} this is expected to crash!
   *
   * @param  the type of elements to concatenate.
   */
  private static class Concatenate extends Combine.CombineFn, List> {
    @Override
    public List createAccumulator() {
      return new ArrayList();
    }

    @Override
    public List addInput(List accumulator, T input) {
      accumulator.add(input);
      return accumulator;
    }

    @Override
    public List mergeAccumulators(Iterable> accumulators) {
      List result = createAccumulator();
      for (List accumulator : accumulators) {
        result.addAll(accumulator);
      }
      return result;
    }

    @Override
    public List extractOutput(List accumulator) {
      return accumulator;
    }

    @Override
    public Coder> getAccumulatorCoder(CoderRegistry registry, Coder inputCoder) {
      return ListCoder.of(inputCoder);
    }

    @Override
    public Coder> getDefaultOutputCoder(CoderRegistry registry, Coder inputCoder) {
      return ListCoder.of(inputCoder);
    }
  }

  /**
   * Creates a primitive {@link PCollectionView}.
   *
   * For internal use only by runner implementors.
   *
   * @param  The type of the elements of the input PCollection
   * @param  The type associated with the {@link PCollectionView} used as a side input
   */
  public static class CreateFlinkPCollectionView
      extends PTransform>, PCollection>> {
    private PCollectionView view;

    private CreateFlinkPCollectionView(PCollectionView view) {
      this.view = view;
    }

    public static  CreateFlinkPCollectionView of(
        PCollectionView view) {
      return new CreateFlinkPCollectionView<>(view);
    }

    @Override
    public PCollection> expand(PCollection> input) {
      return PCollection.createPrimitiveOutputInternal(
          input.getPipeline(), input.getWindowingStrategy(), input.isBounded(), input.getCoder());
    }

    public PCollectionView getView() {
      return view;
    }
  }

  public static class Factory
      implements PTransformOverrideFactory<
          PCollection, PCollection, CreatePCollectionView> {
    public Factory() {}

    @Override
    public PTransformReplacement, PCollection> getReplacementTransform(
        AppliedPTransform<
                PCollection, PCollection, CreatePCollectionView>
            transform) {
      return PTransformReplacement.of(
          (PCollection) Iterables.getOnlyElement(transform.getInputs().values()),
          new CreateStreamingFlinkView(transform.getTransform().getView()));
    }

    @Override
    public Map mapOutputs(
        Map, PValue> outputs, PCollection newOutput) {
      return ReplacementOutputs.singleton(outputs, newOutput);
    }
  }
}