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.worker;
  
  import java.io.IOException;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.ByteArrayShufflePosition;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.NativeReader;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.ShuffleEntry;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.ShuffleEntryReader;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.coders.KvCoder;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.sdk.util.CoderUtils;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.sdk.values.WindowedValues.WindowedValueCoder;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
  
  /**
   * A source that reads from a key-sharded dataset, and returns KVs without any values grouping.
   *
   * @param <K> the type of the keys read from the shuffle
   * @param <V> the type of the values read from the shuffle
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class PartitioningShuffleReader<K, V> extends NativeReader<WindowedValue<KV<K, V>>> {
    final byte[] shuffleReaderConfig;
    final String startShufflePosition;
    final String stopShufflePosition;
    private final BatchModeExecutionContext executionContext;
    private final DataflowOperationContext operationContext;
    Coder<K> keyCoder;
    WindowedValueCoder<V> windowedValueCoder;
  
    public PartitioningShuffleReader(
        PipelineOptions options,
        byte[] shuffleReaderConfig,
        String startShufflePosition,
        String stopShufflePosition,
        Coder<WindowedValue<KV<K, V>>> coder,
        BatchModeExecutionContext executionContext,
        DataflowOperationContext operationContext)
        throws Exception {
      this.shuffleReaderConfig = shuffleReaderConfig;
      this.startShufflePosition = startShufflePosition;
      this.stopShufflePosition = stopShufflePosition;
      this.executionContext = executionContext;
      this.operationContext = operationContext;
      initCoder(coder);
    }
  
    /**
     * Given a {@code WindowedValueCoder<KV<K, V>>}, splits it into a coder for K and a {@code
     * WindowedValueCoder<V>} with the same kind of windows.
     */
    private void initCoder(Coder<WindowedValue<KV<K, V>>> coder) throws Exception {
      if (!(coder instanceof WindowedValueCoder)) {
        throw new Exception("unexpected kind of coder for WindowedValue: " + coder);
      }
      WindowedValueCoder<KV<K, V>> windowedElemCoder = ((WindowedValueCoder<KV<K, V>>) coder);
      Coder<KV<K, V>> elemCoder = windowedElemCoder.getValueCoder();
      if (!(elemCoder instanceof KvCoder)) {
        throw new Exception(
            "unexpected kind of coder for elements read from "
                + "a key-partitioning shuffle: "
                + elemCoder);
      }
      @SuppressWarnings("unchecked")
      KvCoder<K, V> kvCoder = (KvCoder<K, V>) elemCoder;
      this.keyCoder = kvCoder.getKeyCoder();
      windowedValueCoder = windowedElemCoder.withValueCoder(kvCoder.getValueCoder());
    }
  
    @Override
    public NativeReaderIterator<WindowedValue<KV<K, V>>> iterator() throws IOException {
      return iterator(
          new ApplianceShuffleEntryReader(
              shuffleReaderConfig, executionContext, operationContext, false /* no caching */));
    }
  
    /**
     * Creates an iterator on top of the given entry reader.
     *
     * <p>Takes "ownership" of the reader: closes the reader once the iterator is closed.
     */
    PartitioningShuffleReaderIterator<K, V> iterator(ShuffleEntryReader reader) {
      return new PartitioningShuffleReaderIterator<>(this, reader);
    }
  
    /**
     * A ReaderIterator that reads from a ShuffleEntryReader, extracts K and {@code WindowedValue<V>},
     * and returns a constructed {@code WindowedValue<KV>}.
     */
    @VisibleForTesting
    static class PartitioningShuffleReaderIterator<K, V>
        extends NativeReaderIterator<WindowedValue<KV<K, V>>> {
      private Iterator<ShuffleEntry> iterator;
      private WindowedValue<KV<K, V>> current;
      private PartitioningShuffleReader<K, V> shuffleReader;
      private ShuffleEntryReader entryReader;
  
      PartitioningShuffleReaderIterator(
          PartitioningShuffleReader<K, V> shuffleReader, ShuffleEntryReader entryReader) {
        this.iterator =
            entryReader.read(
                shuffleReader.startShufflePosition == null
                    ? null
                    : ByteArrayShufflePosition.fromBase64(shuffleReader.startShufflePosition),
                shuffleReader.stopShufflePosition == null
                    ? null
                    : ByteArrayShufflePosition.fromBase64(shuffleReader.stopShufflePosition));
        this.shuffleReader = shuffleReader;
        this.entryReader = entryReader;
      }
  
      @Override
      public boolean start() throws IOException {
        return advance();
      }
  
      @Override
      public boolean advance() throws IOException {
        if (!iterator.hasNext()) {
          current = null;
          return false;
        }
        ShuffleEntry record = iterator.next();
        K key = CoderUtils.decodeFromByteString(shuffleReader.keyCoder, record.getKey());
        WindowedValue<V> windowedValue =
            CoderUtils.decodeFromByteString(shuffleReader.windowedValueCoder, record.getValue());
        shuffleReader.notifyElementRead(record.length());
        current = windowedValue.withValue(KV.of(key, windowedValue.getValue()));
        return true;
      }
  
      @Override
      public WindowedValue<KV<K, V>> getCurrent() {
        if (current == null) {
          throw new NoSuchElementException();
        }
        return current;
      }
  
      @Override
      public void close() throws IOException {
        entryReader.close();
      }
    }
  }
  