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.NoSuchElementException;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.NativeReader;
  import org.apache.beam.runners.dataflow.worker.windmill.Windmill;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Optional;
  
  /**
   * Base class for iterators that decode messages from bundles inside a {@link Windmill.WorkItem}.
   */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public abstract class WindmillReaderIteratorBase<T>
      extends NativeReader.NativeReaderIterator<WindowedValue<T>> {
    private Windmill.WorkItem work;
    private int bundleIndex = 0;
    private int messageIndex = -1;
    private Optional<WindowedValue<T>> current;
  
    protected WindmillReaderIteratorBase(Windmill.WorkItem work) {
      this.work = work;
    }
  
    @Override
    public boolean start() throws IOException {
      return advance();
    }
  
    @Override
    public boolean advance() throws IOException {
      if (bundleIndex == work.getMessageBundlesCount()
          || messageIndex == work.getMessageBundles(bundleIndex).getMessagesCount()) {
        current = Optional.absent();
        return false;
      }
      ++messageIndex;
      for (; bundleIndex < work.getMessageBundlesCount(); ++bundleIndex, messageIndex = 0) {
        Windmill.InputMessageBundle bundle = work.getMessageBundles(bundleIndex);
        if (messageIndex < bundle.getMessagesCount()) {
          current = Optional.of(decodeMessage(bundle.getMessages(messageIndex)));
          return true;
        }
      }
      current = Optional.absent();
      return false;
    }
  
    protected abstract WindowedValue<T> decodeMessage(Windmill.Message message) throws IOException;
  
    @Override
    public WindowedValue<T> getCurrent() throws NoSuchElementException {
      if (!current.isPresent()) {
        throw new NoSuchElementException();
      }
      return current.get();
    }
  }
  