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Druid Aggregators based on datasketches lib http://datasketches.github.io/
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/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets 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 io.druid.query.aggregation.datasketches.theta;

import com.yahoo.sketches.Family;
import com.yahoo.sketches.theta.SetOperation;
import com.yahoo.sketches.theta.Union;
import io.druid.java.util.common.ISE;
import io.druid.query.aggregation.Aggregator;
import io.druid.segment.BaseObjectColumnValueSelector;

import java.util.List;

public class SketchAggregator implements Aggregator
{
  private final BaseObjectColumnValueSelector selector;
  private final int size;
  private Union union;

  public SketchAggregator(BaseObjectColumnValueSelector selector, int size)
  {
    this.selector = selector;
    this.size = size;
  }

  private void initUnion()
  {
    union = new SynchronizedUnion((Union) SetOperation.builder().setNominalEntries(size).build(Family.UNION));
  }

  @Override
  public void aggregate()
  {
    Object update = selector.getObject();
    if (update == null) {
      return;
    }
    if (union == null) {
      initUnion();
    }
    updateUnion(union, update);
  }

  @Override
  public Object get()
  {
    if (union == null) {
      return SketchHolder.EMPTY;
    }
    //in the code below, I am returning SetOp.getResult(true, null)
    //"true" returns an ordered sketch but slower to compute than unordered sketch.
    //however, advantage of ordered sketch is that they are faster to "union" later
    //given that results from the aggregator will be combined further, it is better
    //to return the ordered sketch here
    return SketchHolder.of(union.getResult(true, null));
  }

  @Override
  public float getFloat()
  {
    throw new UnsupportedOperationException("Not implemented");
  }

  @Override
  public long getLong()
  {
    throw new UnsupportedOperationException("Not implemented");
  }

  @Override
  public double getDouble()
  {
    throw new UnsupportedOperationException("Not implemented");
  }

  @Override
  public void close()
  {
    union = null;
  }

  static void updateUnion(Union union, Object update)
  {
    if (update instanceof SketchHolder) {
      ((SketchHolder) update).updateUnion(union);
    } else if (update instanceof String) {
      union.update((String) update);
    } else if (update instanceof byte[]) {
      union.update((byte[]) update);
    } else if (update instanceof Double) {
      union.update(((Double) update));
    } else if (update instanceof Integer || update instanceof Long) {
      union.update(((Number) update).longValue());
    } else if (update instanceof int[]) {
      union.update((int[]) update);
    } else if (update instanceof long[]) {
      union.update((long[]) update);
    } else if (update instanceof List) {
      for (Object entry : (List) update) {
        union.update(entry.toString());
      }
    } else {
      throw new ISE("Illegal type received while theta sketch merging [%s]", update.getClass());
    }
  }
}