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Beam IO for Google Cloud Pub/Sub Lite
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/*
 * Copyright 2020 Google LLC
 *
 * Licensed 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 com.google.cloud.pubsublite.beam;

import com.google.cloud.pubsublite.Offset;
import com.google.cloud.pubsublite.internal.ExtractStatus;
import com.google.cloud.pubsublite.internal.wire.Committer;
import com.google.cloud.pubsublite.proto.SequencedMessage;
import org.apache.beam.sdk.io.range.OffsetRange;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.SerializableBiFunction;
import org.apache.beam.sdk.transforms.SerializableFunction;
import org.apache.beam.sdk.transforms.splittabledofn.RestrictionTracker;
import org.apache.beam.sdk.transforms.splittabledofn.WatermarkEstimators.MonotonicallyIncreasing;
import org.joda.time.Duration;
import org.joda.time.Instant;

class PerSubscriptionPartitionSdf extends DoFn {
  private final Duration maxSleepTime;
  private final SubscriptionPartitionProcessorFactory processorFactory;
  private final SerializableFunction
      offsetReaderFactory;
  private final SerializableBiFunction<
          SubscriptionPartition, OffsetRange, RestrictionTracker>
      trackerFactory;
  private final SerializableFunction committerFactory;

  PerSubscriptionPartitionSdf(
      Duration maxSleepTime,
      SerializableFunction offsetReaderFactory,
      SerializableBiFunction<
              SubscriptionPartition,
              OffsetRange,
              RestrictionTracker>
          trackerFactory,
      SubscriptionPartitionProcessorFactory processorFactory,
      SerializableFunction committerFactory) {
    this.maxSleepTime = maxSleepTime;
    this.processorFactory = processorFactory;
    this.offsetReaderFactory = offsetReaderFactory;
    this.trackerFactory = trackerFactory;
    this.committerFactory = committerFactory;
  }

  @GetInitialWatermarkEstimatorState
  public Instant getInitialWatermarkState() {
    return Instant.EPOCH;
  }

  @NewWatermarkEstimator
  public MonotonicallyIncreasing newWatermarkEstimator(@WatermarkEstimatorState Instant state) {
    return new MonotonicallyIncreasing(state);
  }

  @ProcessElement
  public ProcessContinuation processElement(
      RestrictionTracker tracker,
      @Element SubscriptionPartition subscriptionPartition,
      OutputReceiver receiver)
      throws Exception {
    try (SubscriptionPartitionProcessor processor =
        processorFactory.newProcessor(subscriptionPartition, tracker, receiver)) {
      processor.start();
      ProcessContinuation result = processor.waitForCompletion(maxSleepTime);
      processor
          .lastClaimed()
          .ifPresent(
              lastClaimedOffset -> {
                Committer committer = committerFactory.apply(subscriptionPartition);
                committer.startAsync().awaitRunning();
                // Commit the next-to-deliver offset.
                try {
                  committer.commitOffset(Offset.of(lastClaimedOffset.value() + 1)).get();
                } catch (Exception e) {
                  throw ExtractStatus.toCanonical(e).underlying;
                }
                committer.stopAsync().awaitTerminated();
              });
      return result;
    }
  }

  @GetInitialRestriction
  public OffsetRange getInitialRestriction(@Element SubscriptionPartition subscriptionPartition) {
    try (InitialOffsetReader reader = offsetReaderFactory.apply(subscriptionPartition)) {
      Offset offset = reader.read();
      return new OffsetRange(offset.value(), Long.MAX_VALUE /* open interval */);
    }
  }

  @NewTracker
  public RestrictionTracker newTracker(
      @Element SubscriptionPartition subscriptionPartition, @Restriction OffsetRange range) {
    return trackerFactory.apply(subscriptionPartition, range);
  }
}