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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.proto.SequencedMessage;
import org.apache.beam.sdk.transforms.MapElements;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.ProcessFunction;
import org.apache.beam.sdk.transforms.Values;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.TypeDescriptor;

/**
 * A transform for deduplicating Pub/Sub Lite messages based on the UUID they were published with.
 */
class UuidDeduplicationTransform
    extends PTransform, PCollection> {
  private final UuidDeduplicationOptions options;

  UuidDeduplicationTransform(UuidDeduplicationOptions options) {
    this.options = options;
  }

  @Override
  public PCollection expand(PCollection input) {
    ProcessFunction> mapWithKeys =
        message -> KV.of(options.uuidExtractor().apply(message), message);
    PCollection> uuidMapped =
        input.apply(
            "MapUuids",
            MapElements.into(new TypeDescriptor>() {}).via(mapWithKeys));
    PCollection> unique =
        uuidMapped.apply("Deduplicate", options.deduplicate());
    return unique.apply("StripUuids", Values.create());
  }
}