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A module that is everything required to understands Druid Segments

There is a newer version: 30.0.1

/*
 * 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.
 */

package org.apache.druid.query;

import com.google.common.base.Preconditions;
import org.apache.druid.common.guava.CombiningSequence;
import org.apache.druid.guice.annotations.PublicApi;
import org.apache.druid.java.util.common.guava.Sequence;
import org.apache.druid.query.context.ResponseContext;

import java.util.Comparator;
import java.util.function.BinaryOperator;
import java.util.function.Function;

/**
 */
@PublicApi
public class ResultMergeQueryRunner extends BySegmentSkippingQueryRunner
{
  private final Function, Comparator> comparatorGenerator;
  private final Function, BinaryOperator> mergeFnGenerator;

  public ResultMergeQueryRunner(
      QueryRunner baseRunner,
      Function, Comparator> comparatorGenerator,
      Function, BinaryOperator> mergeFnGenerator
  )
  {
    super(baseRunner);
    Preconditions.checkNotNull(comparatorGenerator);
    Preconditions.checkNotNull(mergeFnGenerator);
    this.comparatorGenerator = comparatorGenerator;
    this.mergeFnGenerator = mergeFnGenerator;
  }

  @Override
  public Sequence doRun(QueryRunner baseRunner, QueryPlus queryPlus, ResponseContext context)
  {
    Query query = queryPlus.getQuery();
    return CombiningSequence.create(
        baseRunner.run(queryPlus, context),
        comparatorGenerator.apply(query),
        mergeFnGenerator.apply(query));
  }
}