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   * Licensed to the Apache Software Foundation (ASF) under one
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   * 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,
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   * See the License for the specific language governing permissions and
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  package org.apache.beam.sdk.nexmark.queries;
  
  import java.io.Serializable;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.List;
  import org.apache.beam.sdk.nexmark.NexmarkConfiguration;
  import org.apache.beam.sdk.nexmark.NexmarkUtils;
  import org.apache.beam.sdk.nexmark.model.Bid;
  import org.apache.beam.sdk.nexmark.model.Event;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.values.TimestampedValue;
  import org.joda.time.Duration;
  import org.joda.time.Instant;
  
  /** A direct implementation of {@link Query7}. */
  @SuppressWarnings({
    "nullness" // TODO(https://github.com/apache/beam/issues/20497)
  })
  public class Query7Model extends NexmarkQueryModel<Bid> implements Serializable {
    /** Simulator for query 7. */
    private class Simulator extends AbstractSimulator<Event, Bid> {
      /** Bids with highest bid price seen in the current window. */
      private final List<Bid> highestBids;
  
      /** When current window started. */
      private Instant windowStart;
  
      private Instant lastTimestamp;
  
      public Simulator(NexmarkConfiguration configuration) {
        super(NexmarkUtils.standardEventIterator(configuration));
        highestBids = new ArrayList<>();
        windowStart = NexmarkUtils.BEGINNING_OF_TIME;
        lastTimestamp = BoundedWindow.TIMESTAMP_MIN_VALUE;
      }
  
      /** Transfer the currently winning bids into results and retire them. */
      private void retireWindow(Instant timestamp) {
        for (Bid bid : highestBids) {
          addResult(TimestampedValue.of(bid, timestamp));
        }
        highestBids.clear();
      }
  
      /** Keep just the highest price bid. */
      private void captureBid(Bid bid) {
        Iterator<Bid> itr = highestBids.iterator();
        boolean isWinning = true;
        while (itr.hasNext()) {
          Bid existingBid = itr.next();
          if (existingBid.price > bid.price) {
            isWinning = false;
            break;
          }
          NexmarkUtils.info("smaller price: %s", existingBid);
          itr.remove();
        }
        if (isWinning) {
          NexmarkUtils.info("larger price: %s", bid);
          highestBids.add(bid);
        }
      }
  
      @Override
      protected void run() {
        TimestampedValue<Event> timestampedEvent = nextInput();
        if (timestampedEvent == null) {
          // Capture all remaining bids in results.
          retireWindow(lastTimestamp);
          allDone();
          return;
        }
  
        Event event = timestampedEvent.getValue();
        if (event.bid == null) {
          // Ignore non-bid events.
          return;
        }
        lastTimestamp = timestampedEvent.getTimestamp();
        Instant newWindowStart =
            windowStart(
                Duration.standardSeconds(configuration.windowSizeSec),
                Duration.standardSeconds(configuration.windowSizeSec),
                lastTimestamp);
        if (!newWindowStart.equals(windowStart)) {
          // Capture highest priced bids in current window and retire it.
          retireWindow(lastTimestamp);
          windowStart = newWindowStart;
        }
        // Keep only the highest bids.
        captureBid(event.bid);
      }
    }
  
    public Query7Model(NexmarkConfiguration configuration) {
      super(configuration);
    }
  
    @Override
    public AbstractSimulator<?, Bid> simulator() {
      return new Simulator(configuration);
    }
  
    @Override
    protected Collection<String> toCollection(Iterator<TimestampedValue<Bid>> itr) {
      return toValue(itr);
    }
  }
  