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.core;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Set;
  import org.apache.beam.sdk.state.TimeDomain;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.apache.beam.sdk.values.WindowedValue;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Iterables;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.joda.time.Instant;
  
  /**
   * A {@link DoFnRunner} that can refuse to process elements that are not ready, instead returning
   * them via the {@link #processElementInReadyWindows(WindowedValue)}.
   */
  @SuppressWarnings({"nullness", "keyfor"}) // TODO(https://github.com/apache/beam/issues/20497)
  public class SimplePushbackSideInputDoFnRunner<InputT, OutputT>
      implements PushbackSideInputDoFnRunner<InputT, OutputT> {
    private final DoFnRunner<InputT, OutputT> underlying;
    private final Collection<PCollectionView<?>> views;
    private final ReadyCheckingSideInputReader sideInputReader;
  
    // Initialized in startBundle()
    private @Nullable Set<BoundedWindow> notReadyWindows;
  
    public static <InputT, OutputT> SimplePushbackSideInputDoFnRunner<InputT, OutputT> create(
        DoFnRunner<InputT, OutputT> underlying,
        Collection<PCollectionView<?>> views,
        ReadyCheckingSideInputReader sideInputReader) {
      return new SimplePushbackSideInputDoFnRunner<>(underlying, views, sideInputReader);
    }
  
    private SimplePushbackSideInputDoFnRunner(
        DoFnRunner<InputT, OutputT> underlying,
        Collection<PCollectionView<?>> views,
        ReadyCheckingSideInputReader sideInputReader) {
      this.underlying = underlying;
      this.views = views;
      this.sideInputReader = sideInputReader;
    }
  
    @Override
    public DoFn<InputT, OutputT> getFn() {
      return underlying.getFn();
    }
  
    @Override
    public void startBundle() {
      notReadyWindows = new HashSet<>();
      underlying.startBundle();
    }
  
    @Override
    public Iterable<WindowedValue<InputT>> processElementInReadyWindows(WindowedValue<InputT> elem) {
      if (views.isEmpty()) {
        // When there are no side inputs, we can preserve the compressed representation.
        underlying.processElement(elem);
        return Collections.emptyList();
      }
      ImmutableList.Builder<WindowedValue<InputT>> pushedBack = ImmutableList.builder();
      for (WindowedValue<InputT> windowElem : elem.explodeWindows()) {
        BoundedWindow mainInputWindow = Iterables.getOnlyElement(windowElem.getWindows());
        if (isReady(mainInputWindow)) {
          // When there are any side inputs, we have to process the element in each window
          // individually, to disambiguate access to per-window side inputs.
          underlying.processElement(windowElem);
        } else {
          notReadyWindows.add(mainInputWindow);
          pushedBack.add(windowElem);
        }
      }
      return pushedBack.build();
    }
  
    private boolean isReady(BoundedWindow mainInputWindow) {
      if (notReadyWindows.contains(mainInputWindow)) {
        return false;
      }
      for (PCollectionView<?> view : views) {
        BoundedWindow sideInputWindow = view.getWindowMappingFn().getSideInputWindow(mainInputWindow);
        if (!sideInputReader.isReady(view, sideInputWindow)) {
          return false;
        }
      }
      return true;
    }
  
    @Override
    public <KeyT> void onTimer(
        String timerId,
        String timerFamilyId,
        KeyT key,
        BoundedWindow window,
        Instant timestamp,
        Instant outputTimestamp,
        TimeDomain timeDomain) {
      underlying.onTimer(timerId, timerFamilyId, key, window, timestamp, outputTimestamp, timeDomain);
    }
  
    @Override
    public <KeyT> void onWindowExpiration(BoundedWindow window, Instant outputTimestamp, KeyT key) {
      underlying.onWindowExpiration(window, outputTimestamp, key);
    }
  
    @Override
    public void finishBundle() {
      notReadyWindows = null;
      underlying.finishBundle();
    }
  }
  