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;
  
  import org.apache.beam.sdk.runners.AppliedPTransform;
  import org.apache.beam.sdk.runners.PTransformOverrideFactory;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.GroupByKey;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.transforms.Reshuffle;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.transforms.windowing.ReshuffleTrigger;
  import org.apache.beam.sdk.transforms.windowing.TimestampCombiner;
  import org.apache.beam.sdk.transforms.windowing.Window;
  import org.apache.beam.sdk.util.IdentityWindowFn;
  import org.apache.beam.sdk.util.construction.PTransformReplacements;
  import org.apache.beam.sdk.util.construction.SingleInputOutputOverrideFactory;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.WindowingStrategy;
  import org.joda.time.Duration;
  
  /**
   * A {@link PTransformOverrideFactory} that overrides {@link Reshuffle} with a version that does not
   * reify timestamps. Dataflow has special handling of the {@link ReshuffleTrigger} which never
   * buffers elements and outputs elements with their original timestamp.
   */
  class ReshuffleOverrideFactory<K, V>
      extends SingleInputOutputOverrideFactory<
          PCollection<KV<K, V>>, PCollection<KV<K, V>>, Reshuffle<K, V>> {
    @Override
    public PTransformReplacement<PCollection<KV<K, V>>, PCollection<KV<K, V>>>
        getReplacementTransform(
            AppliedPTransform<PCollection<KV<K, V>>, PCollection<KV<K, V>>, Reshuffle<K, V>>
                transform) {
      return PTransformOverrideFactory.PTransformReplacement.of(
          PTransformReplacements.getSingletonMainInput(transform), new ReshuffleWithOnlyTrigger<>());
    }
  
    private static class ReshuffleWithOnlyTrigger<K, V>
        extends PTransform<PCollection<KV<K, V>>, PCollection<KV<K, V>>> {
      @Override
      public PCollection<KV<K, V>> expand(PCollection<KV<K, V>> input) {
        WindowingStrategy<?, ?> originalStrategy = input.getWindowingStrategy();
        // If the input has already had its windows merged, then the GBK that performed the merge
        // will have set originalStrategy.getWindowFn() to InvalidWindows, causing the GBK contained
        // here to fail. Instead, we install a valid WindowFn that leaves all windows unchanged.
        Window<KV<K, V>> rewindow =
            Window.<KV<K, V>>into(
                    new IdentityWindowFn<>(originalStrategy.getWindowFn().windowCoder()))
                .triggering(new ReshuffleTrigger<>())
                .discardingFiredPanes()
                .withTimestampCombiner(TimestampCombiner.EARLIEST)
                .withAllowedLateness(Duration.millis(BoundedWindow.TIMESTAMP_MAX_VALUE.getMillis()));
  
        return input
            .apply(rewindow)
            .apply(GroupByKey.create())
            // Set the windowing strategy directly, so that it doesn't get counted as the user having
            // set allowed lateness.
            .setWindowingStrategyInternal(originalStrategy)
            .apply(
                "ExpandIterable",
                ParDo.of(
                    new DoFn<KV<K, Iterable<V>>, KV<K, V>>() {
                      @ProcessElement
                      public void processElement(ProcessContext c) {
                        K key = c.element().getKey();
                        for (V value : c.element().getValue()) {
                          c.output(KV.of(key, value));
                        }
                      }
                    }));
      }
    }
  }
  