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.core;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.transforms.Materializations;
  import org.apache.beam.sdk.transforms.Materializations.MultimapView;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.FluentIterable;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** An in-memory representation of {@link MultimapView}. */
  @SuppressWarnings({
    "rawtypes", // TODO(https://github.com/apache/beam/issues/20447)
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class InMemoryMultimapSideInputView<K, V> implements Materializations.MultimapView<K, V> {
    /** An empty {@link MultimapView}. */
    private static final MultimapView EMPTY =
        new MultimapView() {
          @Override
          public Iterable get() {
            return Collections.emptyList();
          }
  
          @Override
          public Iterable get(@Nullable Object k) {
            return Collections.emptyList();
          }
        };
  
    /**
     * Creates a {@link MultimapView} from the provided values. The provided {@link Coder} is used to
     * guarantee structural equality for keys instead of assuming Java object equality.
     */
    public static <K, V> MultimapView<K, V> fromIterable(
        Coder<K> keyCoder, Iterable<KV<K, V>> values) {
      // We specifically use a hash map to allow for null keys
      Map<Object, KV<K, List<V>>> data = new HashMap<>();
  
      for (KV<K, V> value : values) {
        KV<K, List<V>> keyedValues =
            data.computeIfAbsent(
                keyCoder.structuralValue(value.getKey()),
                o -> KV.of(value.getKey(), new ArrayList<>()));
        keyedValues.getValue().add(value.getValue());
      }
      return new InMemoryMultimapSideInputView(keyCoder, data);
    }
  
    /** Returns an empty {@link MultimapView}. */
    public static <K, V> MultimapView<K, V> empty() {
      return EMPTY;
    }
  
    private final Coder<K> keyCoder;
    private final Map<Object, KV<K, List<V>>> structuralKeyToValuesMap;
  
    private InMemoryMultimapSideInputView(Coder<K> keyCoder, Map<Object, KV<K, List<V>>> data) {
      this.keyCoder = keyCoder;
      this.structuralKeyToValuesMap = data;
    }
  
    @Override
    public Iterable<K> get() {
      return Iterables.unmodifiableIterable(
          FluentIterable.from(structuralKeyToValuesMap.values())
              .transform(kListKV -> kListKV.getKey()));
    }
  
    @Override
    public Iterable<V> get(K k) {
      KV<K, List<V>> records = structuralKeyToValuesMap.get(keyCoder.structuralValue(k));
      if (records == null) {
        return Collections.emptyList();
      }
      return records.getValue();
    }
  }
  