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.flink.translation.functions;
  
  import java.util.Collections;
  import java.util.Objects;
  import org.apache.beam.runners.core.SideInputReader;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.transforms.windowing.PaneInfo;
  import org.apache.beam.sdk.transforms.windowing.TimestampCombiner;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.sdk.values.WindowedValues;
  import org.apache.beam.sdk.values.WindowingStrategy;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterators;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.PeekingIterator;
  import org.apache.flink.api.java.tuple.Tuple2;
  import org.apache.flink.util.Collector;
  import org.joda.time.Instant;
  
  /**
   * A Flink combine runner takes elements pre-grouped by window and produces output after seeing all
   * input.
   */
  @SuppressWarnings({"keyfor", "nullness"}) // TODO(https://github.com/apache/beam/issues/20497)
  public class SingleWindowFlinkCombineRunner<K, InputT, AccumT, OutputT, W extends BoundedWindow>
      extends AbstractFlinkCombineRunner<K, InputT, AccumT, OutputT, W> {
  
    @Override
    public void combine(
        FlinkCombiner<K, InputT, AccumT, OutputT> flinkCombiner,
        WindowingStrategy<Object, W> windowingStrategy,
        SideInputReader sideInputReader,
        PipelineOptions options,
        Iterable<WindowedValue<KV<K, InputT>>> elements,
        Collector<WindowedValue<KV<K, OutputT>>> out) {
      final TimestampCombiner timestampCombiner = windowingStrategy.getTimestampCombiner();
      final PeekingIterator<WindowedValue<KV<K, InputT>>> iterator =
          Iterators.peekingIterator(elements.iterator());
  
      @SuppressWarnings("unchecked")
      final W currentWindow = (W) Iterables.getOnlyElement(iterator.peek().getWindows());
      final K key = iterator.peek().getValue().getKey();
  
      Tuple2<AccumT, Instant> combinedState = null;
      while (iterator.hasNext()) {
        final WindowedValue<KV<K, InputT>> currentValue = iterator.next();
        Preconditions.checkState(
            currentWindow.equals(Iterables.getOnlyElement(currentValue.getWindows())),
            "Incompatible windows.");
        if (combinedState == null) {
          AccumT accumT =
              flinkCombiner.firstInput(
                  key,
                  currentValue.getValue().getValue(),
                  options,
                  sideInputReader,
                  Collections.singleton(currentWindow));
          Instant windowTimestamp =
              timestampCombiner.assign(currentWindow, currentValue.getTimestamp());
          combinedState = new Tuple2<>(accumT, windowTimestamp);
        } else {
          combinedState.f0 =
              flinkCombiner.addInput(
                  key,
                  combinedState.f0,
                  currentValue.getValue().getValue(),
                  options,
                  sideInputReader,
                  Collections.singleton(currentWindow));
          combinedState.f1 =
              timestampCombiner.combine(
                  combinedState.f1,
                  timestampCombiner.assign(currentWindow, currentValue.getTimestamp()));
        }
      }
  
      // Output the final value of combiners.
      Objects.requireNonNull(combinedState);
      final AccumT accumulator = combinedState.f0;
      final Instant windowTimestamp = combinedState.f1;
      out.collect(
          WindowedValues.of(
              KV.of(
                  key,
                  flinkCombiner.extractOutput(
                      key,
                      accumulator,
                      options,
                      sideInputReader,
                      Collections.singleton(currentWindow))),
              windowTimestamp,
              currentWindow,
              PaneInfo.NO_FIRING));
    }
  }
  