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A module that is everything required to understands Druid Segments
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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.
 */

package org.apache.druid.query;

import org.apache.druid.java.util.common.guava.Sequence;
import org.apache.druid.java.util.emitter.service.ServiceEmitter;
import org.apache.druid.query.context.ResponseContext;

import java.util.concurrent.atomic.AtomicLong;
import java.util.function.Function;

public class FluentQueryRunner implements QueryRunner
{
  @SuppressWarnings("unchecked")
  public static > FluentQueryRunner create(
      QueryRunner runner,
      QueryToolChest toolchest
  )
  {
    return new FluentQueryRunner<>(runner, (QueryToolChest>) toolchest);
  }

  private final QueryToolChest> toolChest;
  private final QueryRunner baseRunner;

  public FluentQueryRunner(QueryRunner runner, QueryToolChest> toolChest)
  {
    this.baseRunner = runner;
    this.toolChest = toolChest;
  }

  @Override
  public Sequence run(QueryPlus queryPlus, ResponseContext responseContext)
  {
    return baseRunner.run(queryPlus, responseContext);
  }

  public FluentQueryRunner from(QueryRunner runner)
  {
    return new FluentQueryRunner(runner, toolChest);
  }

  public FluentQueryRunner applyPostMergeDecoration()
  {
    return from(new FinalizeResultsQueryRunner<>(toolChest.postMergeQueryDecoration(baseRunner), toolChest));
  }

  public FluentQueryRunner applyPreMergeDecoration()
  {
    return from(new UnionQueryRunner<>(toolChest.preMergeQueryDecoration(baseRunner)));
  }

  public FluentQueryRunner emitCPUTimeMetric(ServiceEmitter emitter)
  {
    return emitCPUTimeMetric(emitter, new AtomicLong(0L));
  }

  public FluentQueryRunner emitCPUTimeMetric(ServiceEmitter emitter, AtomicLong accumulator)
  {
    return from(
        CPUTimeMetricQueryRunner.safeBuild(
            baseRunner,
            toolChest,
            emitter,
            accumulator,
            true
        )
    );
  }

  public FluentQueryRunner postProcess(PostProcessingOperator postProcessing)
  {
    return from(postProcessing != null ? postProcessing.postProcess(baseRunner) : baseRunner);
  }

  public FluentQueryRunner mergeResults()
  {
    return from(toolChest.mergeResults(baseRunner));
  }

  public FluentQueryRunner map(final Function, QueryRunner> mapFn)
  {
    return from(mapFn.apply(baseRunner));
  }

  /**
   * Sets the toString of the QueryRunner.  This is used because QueryRunner objects are often used as parameters for
   * tests and the toString() value of the QueryRunners are used for the name of the test.
   *
   * This method doesn't return a FluentQueryRunner because it breaks the fluency.
   *
   * @param toStringValue the value that the resulting QueryRunner should return from its toString method.
   * @return a QueryRunner that will return toStringValue from its toString method
   */
  public QueryRunner setToString(String toStringValue)
  {
    return new QueryRunner()
    {
      @Override
      public Sequence run(QueryPlus queryPlus, ResponseContext responseContext)
      {
        return FluentQueryRunner.this.run(queryPlus, responseContext);
      }

      @Override
      public String toString()
      {
        return toStringValue;
      }
    };
  }
}