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 static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.api.services.dataflow.model.ApproximateReportedProgress;
  import com.google.api.services.dataflow.model.ApproximateSplitRequest;
  import com.google.api.services.dataflow.model.ConcatPosition;
  import com.google.api.services.dataflow.model.Source;
  import java.io.IOException;
  import java.util.Iterator;
  import java.util.List;
  import java.util.NoSuchElementException;
  import org.apache.beam.runners.dataflow.util.CloudObject;
  import org.apache.beam.runners.dataflow.util.CloudObjects;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.NativeReader;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.io.range.OffsetRangeTracker;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * A {@link NativeReader} that reads elements from a given set of encoded {@link Source}s. Creates
   * {@link NativeReader}s for sources lazily, i.e. only when elements from the particular {@code
   * NativeReader} are about to be read.
   *
   * <p>This class does not cache {@link NativeReader}s and instead creates new set of {@link
   * NativeReader}s for every new {@link ConcatIterator}. Because of this, multiple {@link
   * ConcatIterator}s created using the same {@link ConcatReader} will not be able to share any state
   * between each other. This design was chosen since keeping a large number of {@link NativeReader}
   * objects alive within a single {@link ConcatReader} could be highly memory consuming.
   *
   * <p>For progress reporting and dynamic work rebalancing purposes, {@link ConcatIterator} uses a
   * position of type {@link ConcatPosition}. Progress reporting and dynamic work rebalancing
   * currently work only at the granularity of full sources being concatenated.
   *
   * @param <T> Type of the elements read by the {@link NativeReader}s.
   */
  @SuppressWarnings({
    "rawtypes", // TODO(https://github.com/apache/beam/issues/20447)
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class ConcatReader<T> extends NativeReader<T> {
    private static final Logger LOG = LoggerFactory.getLogger(ConcatReader.class);
  
    public static final String SOURCE_NAME = "ConcatSource";
  
    private final List<Source> sources;
    private final PipelineOptions options;
    private final DataflowExecutionContext executionContext;
    private final ReaderFactory readerFactory;
    private final DataflowOperationContext operationContext;
  
    /** Create a {@link ConcatReader} using a given list of encoded {@link Source}s. */
    public ConcatReader(
        ReaderFactory readerFactory,
        PipelineOptions options,
        DataflowExecutionContext executionContext,
        DataflowOperationContext operationContext,
        List<Source> sources) {
      this.operationContext = operationContext;
      Preconditions.checkNotNull(sources);
      this.readerFactory = readerFactory;
      this.sources = sources;
      this.options = options;
      this.executionContext = executionContext;
    }
  
    public Iterator<Source> getSources() {
      return sources.iterator();
    }
  
    @Override
    public ConcatIterator<T> iterator() throws IOException {
      return new ConcatIterator<T>(
          readerFactory, options, executionContext, operationContext, sources);
    }
  
    @VisibleForTesting
    static class ConcatIterator<T> extends NativeReaderIterator<T> {
      private int currentIteratorIndex = -1;
      private @Nullable NativeReaderIterator<T> currentIterator = null;
      private final List<Source> sources;
      private final PipelineOptions options;
      private final DataflowExecutionContext executionContext;
      private final DataflowOperationContext operationContext;
      private final OffsetRangeTracker rangeTracker;
      private final ReaderFactory readerFactory;
  
      public ConcatIterator(
          ReaderFactory readerFactory,
          PipelineOptions options,
          DataflowExecutionContext executionContext,
          DataflowOperationContext operationContext,
          List<Source> sources) {
        this.readerFactory = readerFactory;
        this.sources = sources;
        this.options = options;
        this.executionContext = executionContext;
        this.operationContext = operationContext;
        this.rangeTracker = new OffsetRangeTracker(0, sources.size());
      }
  
      @Override
      public boolean start() throws IOException {
        return advance();
      }
  
      @Override
      public boolean advance() throws IOException {
        while (true) {
          // Invariant: we call currentIterator.start() immediately when opening an iterator
          // (below). So if currentIterator != null, then start() has already been called on it.
          if (currentIterator != null && currentIterator.advance()) {
            // Happy case: current iterator has a next record.
            return true;
          }
          // Now current iterator is either non-existent or exhausted.
          // Close it, and try opening a new one.
          if (currentIterator != null) {
            currentIterator.close();
            currentIterator = null;
          }
  
          if (!rangeTracker.tryReturnRecordAt(true, currentIteratorIndex + 1)) {
            return false;
          }
          currentIteratorIndex++;
          if (currentIteratorIndex == sources.size()) {
            // All sources were read.
            return false;
          }
  
          Source currentSource = sources.get(currentIteratorIndex);
          try {
            Coder<?> coder = null;
            if (currentSource.getCodec() != null) {
              coder =
                  CloudObjects.coderFromCloudObject(CloudObject.fromSpec(currentSource.getCodec()));
            }
            @SuppressWarnings("unchecked")
            NativeReader<T> currentReader =
                (NativeReader<T>)
                    readerFactory.create(
                        CloudObject.fromSpec(currentSource.getSpec()),
                        coder,
                        options,
                        executionContext,
                        operationContext);
            currentIterator = currentReader.iterator();
          } catch (Exception e) {
            throw new IOException("Failed to create a reader for source: " + currentSource, e);
          }
          if (!currentIterator.start()) {
            currentIterator.close();
            currentIterator = null;
            continue;
          }
          // Happy case: newly opened iterator has a first record.
          return true;
        }
      }
  
      @Override
      public T getCurrent() throws NoSuchElementException {
        if (currentIterator == null) {
          throw new NoSuchElementException();
        }
        return currentIterator.getCurrent();
      }
  
      @Override
      public void close() throws IOException {
        if (currentIterator != null) {
          currentIterator.close();
        }
      }
  
      @Override
      public Progress getProgress() {
        if (currentIteratorIndex < 0) {
          // Reading has not been started yet.
          return null;
        }
  
        if (currentIterator == null) {
          // Reading has been finished.
          throw new UnsupportedOperationException("Can't report progress of a finished iterator");
        }
  
        ConcatPosition concatPosition = new ConcatPosition();
        concatPosition.setIndex(currentIteratorIndex);
        Progress progressOfCurrentIterator = currentIterator.getProgress();
        if (!(progressOfCurrentIterator instanceof SourceTranslationUtils.DataflowReaderProgress)) {
          throw new IllegalArgumentException(
              "Cannot process progress "
                  + progressOfCurrentIterator
                  + " since ConcatReader can only handle readers that generate a progress of type "
                  + "DataflowReaderProgress");
        }
        com.google.api.services.dataflow.model.Position positionOfCurrentIterator =
            ((SourceTranslationUtils.DataflowReaderProgress) progressOfCurrentIterator)
                .cloudProgress.getPosition();
  
        if (positionOfCurrentIterator != null) {
          concatPosition.setPosition(positionOfCurrentIterator);
        }
  
        ApproximateReportedProgress progress = new ApproximateReportedProgress();
        com.google.api.services.dataflow.model.Position currentPosition =
            new com.google.api.services.dataflow.model.Position();
        currentPosition.setConcatPosition(concatPosition);
        progress.setPosition(currentPosition);
  
        return SourceTranslationUtils.cloudProgressToReaderProgress(progress);
      }
  
      @Override
      public DynamicSplitResult requestDynamicSplit(DynamicSplitRequest splitRequest) {
        checkNotNull(splitRequest);
  
        ApproximateSplitRequest splitProgress =
            SourceTranslationUtils.splitRequestToApproximateSplitRequest(splitRequest);
        com.google.api.services.dataflow.model.Position cloudPosition = splitProgress.getPosition();
        if (cloudPosition == null) {
          LOG.warn("Concat only supports split at a Position. Requested: {}", splitRequest);
          return null;
        }
  
        ConcatPosition concatPosition = cloudPosition.getConcatPosition();
        if (concatPosition == null) {
          LOG.warn(
              "ConcatReader only supports split at a ConcatPosition. Requested: {}", cloudPosition);
          return null;
        }
  
        java.lang.Integer index = concatPosition.getIndex();
        if (index == null) {
          index = 0;
        }
  
        if (rangeTracker.trySplitAtPosition(index)) {
          com.google.api.services.dataflow.model.Position positionToSplit =
              new com.google.api.services.dataflow.model.Position();
          positionToSplit.setConcatPosition(
              new ConcatPosition().setIndex((int) rangeTracker.getStopPosition().longValue()));
          return new DynamicSplitResultWithPosition(
              SourceTranslationUtils.cloudPositionToReaderPosition(positionToSplit));
        } else {
          LOG.debug("Could not perform the dynamic split request " + splitRequest);
          return null;
        }
      }
    }
  }
  