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   * 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.
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  package org.apache.beam.sdk.nexmark.queries;
  
  import org.apache.beam.sdk.nexmark.NexmarkConfiguration;
  import org.apache.beam.sdk.nexmark.model.Auction;
  import org.apache.beam.sdk.nexmark.model.Event;
  import org.apache.beam.sdk.nexmark.model.IdNameReserve;
  import org.apache.beam.sdk.nexmark.model.Person;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.transforms.join.CoGbkResult;
  import org.apache.beam.sdk.transforms.join.CoGroupByKey;
  import org.apache.beam.sdk.transforms.join.KeyedPCollectionTuple;
  import org.apache.beam.sdk.transforms.windowing.FixedWindows;
  import org.apache.beam.sdk.transforms.windowing.Window;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.joda.time.Duration;
  
  /**
   * Query 8, 'Monitor New Users'. Select people who have entered the system and created auctions in
   * the last 12 hours, updated every 12 hours. In CQL syntax:
   *
   * <pre>
   * SELECT Rstream(P.id, P.name, A.reserve)
   * FROM Person [RANGE 12 HOUR] P, Auction [RANGE 12 HOUR] A
   * WHERE P.id = A.seller;
   * </pre>
   *
   * <p>To make things a bit more dynamic and easier to test we'll use a much shorter window.
   */
  public class Query8 extends NexmarkQueryTransform<IdNameReserve> {
    private final NexmarkConfiguration configuration;
  
    public Query8(NexmarkConfiguration configuration) {
      super("Query8");
      this.configuration = configuration;
    }
  
    @Override
    public PCollection<IdNameReserve> expand(PCollection<Event> events) {
      // Window and key new people by their id.
      PCollection<KV<Long, Person>> personsById =
          events
              .apply(NexmarkQueryUtil.JUST_NEW_PERSONS)
              .apply(
                  "Query8.WindowPersons",
                  Window.into(FixedWindows.of(Duration.standardSeconds(configuration.windowSizeSec))))
              .apply("PersonById", NexmarkQueryUtil.PERSON_BY_ID);
  
      // Window and key new auctions by their id.
      PCollection<KV<Long, Auction>> auctionsBySeller =
          events
              .apply(NexmarkQueryUtil.JUST_NEW_AUCTIONS)
              .apply(
                  "Query8.WindowAuctions",
                  Window.into(FixedWindows.of(Duration.standardSeconds(configuration.windowSizeSec))))
              .apply("AuctionBySeller", NexmarkQueryUtil.AUCTION_BY_SELLER);
  
      // Join people and auctions and project the person id, name and auction reserve price.
      return KeyedPCollectionTuple.of(NexmarkQueryUtil.PERSON_TAG, personsById)
          .and(NexmarkQueryUtil.AUCTION_TAG, auctionsBySeller)
          .apply(CoGroupByKey.create())
          .apply(
              name + ".Select",
              ParDo.of(
                  new DoFn<KV<Long, CoGbkResult>, IdNameReserve>() {
                    @ProcessElement
                    public void processElement(ProcessContext c) {
                      @Nullable
                      Person person =
                          c.element().getValue().getOnly(NexmarkQueryUtil.PERSON_TAG, null);
                      if (person == null) {
                        // Person was not created in last window period.
                        return;
                      }
                      for (Auction auction :
                          c.element().getValue().getAll(NexmarkQueryUtil.AUCTION_TAG)) {
                        c.output(new IdNameReserve(person.id, person.name, auction.reserve));
                      }
                    }
                  }));
    }
  }
  