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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 static com.google.cloud.pubsublite.internal.ExtractStatus.toCanonical;
import static com.google.cloud.pubsublite.internal.UncheckedApiPreconditions.checkArgument;

import com.google.api.gax.rpc.ApiException;
import com.google.cloud.pubsublite.AdminClient;
import com.google.cloud.pubsublite.AdminClientSettings;
import com.google.cloud.pubsublite.Offset;
import com.google.cloud.pubsublite.Partition;
import com.google.cloud.pubsublite.TopicPath;
import com.google.cloud.pubsublite.internal.wire.Committer;
import com.google.cloud.pubsublite.internal.wire.Subscriber;
import com.google.cloud.pubsublite.proto.SequencedMessage;
import com.google.common.base.Stopwatch;
import com.google.common.math.LongMath;
import java.util.List;
import java.util.function.Consumer;
import java.util.stream.Collectors;
import org.apache.beam.sdk.transforms.DoFn.OutputReceiver;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.ParDo;
import org.apache.beam.sdk.transforms.splittabledofn.RestrictionTracker;
import org.apache.beam.sdk.values.PBegin;
import org.apache.beam.sdk.values.PCollection;
import org.joda.time.Duration;

class SubscribeTransform extends PTransform> {
  private final SubscriberOptions options;

  SubscribeTransform(SubscriberOptions options) {
    this.options = options;
  }

  private void checkSubscription(SubscriptionPartition subscriptionPartition) throws ApiException {
    checkArgument(subscriptionPartition.subscription().equals(options.subscriptionPath()));
  }

  private Subscriber newSubscriber(
      Partition partition, Offset initialOffset, Consumer> consumer) {
    try {
      return options
          .getSubscriberFactory(partition, initialOffset)
          .newSubscriber(
              messages ->
                  consumer.accept(
                      messages.stream()
                          .map(message -> message.toProto())
                          .collect(Collectors.toList())));
    } catch (Throwable t) {
      throw toCanonical(t).underlying;
    }
  }

  private SubscriptionPartitionProcessor newPartitionProcessor(
      SubscriptionPartition subscriptionPartition,
      RestrictionTracker tracker,
      OutputReceiver receiver)
      throws ApiException {
    checkSubscription(subscriptionPartition);
    return new SubscriptionPartitionProcessorImpl(
        tracker,
        receiver,
        consumer ->
            newSubscriber(
                subscriptionPartition.partition(),
                Offset.of(tracker.currentRestriction().getRange().getFrom()),
                consumer),
        options.flowControlSettings());
  }

  private TopicBacklogReader newBacklogReader(SubscriptionPartition subscriptionPartition) {
    checkSubscription(subscriptionPartition);
    return options.getBacklogReader(subscriptionPartition.partition());
  }

  private TrackerWithProgress newRestrictionTracker(
      TopicBacklogReader backlogReader, OffsetByteRange initial) {
    return new OffsetByteRangeTracker(
        initial,
        backlogReader,
        Stopwatch.createUnstarted(),
        options.minBundleTimeout(),
        LongMath.saturatedMultiply(options.flowControlSettings().bytesOutstanding(), 10));
  }

  private InitialOffsetReader newInitialOffsetReader(SubscriptionPartition subscriptionPartition) {
    checkSubscription(subscriptionPartition);
    return options.getInitialOffsetReader(subscriptionPartition.partition());
  }

  private Committer newCommitter(SubscriptionPartition subscriptionPartition) {
    checkSubscription(subscriptionPartition);
    return options.getCommitter(subscriptionPartition.partition());
  }

  private TopicPath getTopicPath() {
    try (AdminClient admin =
        AdminClient.create(
            AdminClientSettings.newBuilder()
                .setRegion(options.subscriptionPath().location().extractRegion())
                .build())) {
      return TopicPath.parse(admin.getSubscription(options.subscriptionPath()).get().getTopic());
    } catch (Throwable t) {
      throw toCanonical(t).underlying;
    }
  }

  @Override
  public PCollection expand(PBegin input) {
    PCollection subscriptionPartitions;
    subscriptionPartitions =
        input.apply(new SubscriptionPartitionLoader(getTopicPath(), options.subscriptionPath()));

    return subscriptionPartitions.apply(
        ParDo.of(
            new PerSubscriptionPartitionSdf(
                // Ensure we read for at least 5 seconds more than the bundle timeout.
                options.minBundleTimeout().plus(Duration.standardSeconds(5)),
                new ManagedBacklogReaderFactoryImpl(this::newBacklogReader),
                this::newInitialOffsetReader,
                this::newRestrictionTracker,
                this::newPartitionProcessor,
                this::newCommitter)));
  }
}