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 com.google.api.client.util.Preconditions.checkNotNull;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects.firstNonNull;
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  
  import com.google.api.services.dataflow.model.ApproximateReportedProgress;
  import java.io.IOException;
  import java.util.List;
  import java.util.NoSuchElementException;
  import java.util.Optional;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.NativeReader;
  import org.apache.beam.sdk.coders.Coder;
  import org.apache.beam.sdk.coders.CoderException;
  import org.apache.beam.sdk.io.range.OffsetRangeTracker;
  import org.apache.beam.sdk.util.CoderUtils;
  import org.apache.beam.sdk.util.StringUtils;
  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 source that yields a set of precomputed elements.
   *
   * @param <T> the type of the elements read from the source
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class InMemoryReader<T> extends NativeReader<T> {
    private static final Logger LOG = LoggerFactory.getLogger(InMemoryReader.class);
  
    final List<String> encodedElements;
    final int startIndex;
    final int endIndex;
    final Coder<T> coder;
  
    public InMemoryReader(
        List<String> encodedElements,
        @Nullable Integer startIndex,
        @Nullable Integer endIndex,
        Coder<T> coder) {
      checkNotNull(encodedElements);
      this.encodedElements = encodedElements;
      int maxIndex = encodedElements.size();
      this.startIndex = Math.min(maxIndex, firstNonNull(startIndex, 0));
      this.endIndex = Math.min(maxIndex, firstNonNull(endIndex, maxIndex));
      checkArgument(this.startIndex >= 0, "negative start index: %s", startIndex);
      checkArgument(
          this.endIndex >= this.startIndex,
          "end index before start: [%s, %s)",
          this.startIndex,
          this.endIndex);
      this.coder = coder;
    }
  
    @Override
    public InMemoryReaderIterator iterator() throws IOException {
      return new InMemoryReaderIterator();
    }
  
    /** A ReaderIterator that yields an in-memory list of elements. */
    class InMemoryReaderIterator extends NativeReaderIterator<T> {
      @VisibleForTesting OffsetRangeTracker tracker;
      private @Nullable Integer lastReturnedIndex;
      private Optional<T> current;
  
      public InMemoryReaderIterator() {
        this.tracker = new OffsetRangeTracker(startIndex, endIndex);
        this.lastReturnedIndex = null;
      }
  
      @Override
      public boolean start() throws IOException {
        Preconditions.checkState(lastReturnedIndex == null, "Already started");
        if (!tracker.tryReturnRecordAt(true, startIndex)) {
          current = Optional.empty();
          return false;
        }
        current = Optional.of(decode(encodedElements.get(startIndex)));
        lastReturnedIndex = startIndex;
        return true;
      }
  
      @Override
      public boolean advance() throws IOException {
        Preconditions.checkNotNull(lastReturnedIndex, "Not started");
        if (!tracker.tryReturnRecordAt(true, (long) lastReturnedIndex + 1)) {
          current = Optional.empty();
          return false;
        }
        ++lastReturnedIndex;
        current = Optional.of(decode(encodedElements.get(lastReturnedIndex)));
        return true;
      }
  
      @Override
      public T getCurrent() throws NoSuchElementException {
        return current.get();
      }
  
      private T decode(String encodedElementString) throws CoderException {
        // TODO: Replace with the real encoding used by the
        // front end, when we know what it is.
        byte[] encodedElement = StringUtils.jsonStringToByteArray(encodedElementString);
        notifyElementRead(encodedElement.length);
        return CoderUtils.decodeFromByteArray(coder, encodedElement);
      }
  
      @Override
      public Progress getProgress() {
        if (lastReturnedIndex == null) {
          return null;
        }
        // Currently we assume that only a record index position is reported as
        // current progress. An implementer can override this method to update
        // other metrics, e.g. completion percentage or remaining time.
        com.google.api.services.dataflow.model.Position currentPosition =
            new com.google.api.services.dataflow.model.Position();
        currentPosition.setRecordIndex((long) lastReturnedIndex);
  
        ApproximateReportedProgress progress = new ApproximateReportedProgress();
        progress.setPosition(currentPosition);
  
        return SourceTranslationUtils.cloudProgressToReaderProgress(progress);
      }
  
      @Override
      public double getRemainingParallelism() {
        // Use the starting index if no elements have yet been returned.
        return tracker.getStopPosition() - firstNonNull(lastReturnedIndex, startIndex);
      }
  
      @Override
      public DynamicSplitResult requestDynamicSplit(DynamicSplitRequest splitRequest) {
        checkNotNull(splitRequest);
  
        com.google.api.services.dataflow.model.Position splitPosition =
            SourceTranslationUtils.splitRequestToApproximateSplitRequest(splitRequest).getPosition();
        if (splitPosition == null) {
          LOG.warn("InMemoryReader only supports split at a Position. Requested: {}", splitRequest);
          return null;
        }
  
        Long splitIndex = splitPosition.getRecordIndex();
        if (splitIndex == null) {
          LOG.warn(
              "InMemoryReader only supports split at a record index. Requested: {}", splitPosition);
          return null;
        }
  
        if (!tracker.trySplitAtPosition(splitIndex)) {
          return null;
        }
        return new DynamicSplitResultWithPosition(
            SourceTranslationUtils.cloudPositionToReaderPosition(splitPosition));
      }
  
      @Override
      public @Nullable DynamicSplitResult requestCheckpoint() {
        if (!tracker.trySplitAtPosition(lastReturnedIndex + 1)) {
          return null;
        }
        com.google.api.services.dataflow.model.Position splitPosition =
            new com.google.api.services.dataflow.model.Position();
        splitPosition.setRecordIndex((long) lastReturnedIndex + 1);
        return new DynamicSplitResultWithPosition(
            SourceTranslationUtils.cloudPositionToReaderPosition(splitPosition));
      }
    }
  }
  