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.extensions.euphoria.core.translate;
  
  import static java.util.Objects.requireNonNull;
  
  import java.util.Objects;
  import org.apache.beam.sdk.extensions.euphoria.core.client.functional.UnaryFunction;
  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.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.TypeDescriptor;
  import org.apache.beam.sdk.values.TypeDescriptors;
  
  /** Key extracting utility transformation shared among operator translators. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  class ExtractKey<KeyT, ValueT>
      extends PTransform<PCollection<ValueT>, PCollection<KV<KeyT, ValueT>>> {
  
    private static class ExtractKeyFn<KeyT, InputT> extends DoFn<InputT, KV<KeyT, InputT>> {
  
      private final UnaryFunction<InputT, KeyT> keyExtractor;
  
      ExtractKeyFn(UnaryFunction<InputT, KeyT> keyExtractor) {
        this.keyExtractor = keyExtractor;
      }
  
      @SuppressWarnings("unused")
      @ProcessElement
      public void processElement(ProcessContext c) {
        final InputT element = c.element();
        final KeyT key = keyExtractor.apply(element);
        c.output(KV.of(key, element));
      }
    }
  
    private final UnaryFunction<ValueT, KeyT> keyExtractor;
    private final TypeDescriptor<KeyT> keyType;
  
    ExtractKey(UnaryFunction<ValueT, KeyT> keyExtractor, TypeDescriptor<KeyT> keyType) {
      this.keyExtractor = requireNonNull(keyExtractor);
      this.keyType = requireNonNull(keyType);
    }
  
    @Override
    public PCollection<KV<KeyT, ValueT>> expand(PCollection<ValueT> input) {
      Objects.requireNonNull(input.getTypeDescriptor());
      return input
          .apply(ParDo.of(new ExtractKeyFn<>(keyExtractor)))
          .setTypeDescriptor(TypeDescriptors.kvs(keyType, input.getTypeDescriptor()));
    }
  }
  