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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.common.lucene.search.function;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.util.StringHelper;
import org.elasticsearch.index.fielddata.AtomicFieldData;
import org.elasticsearch.index.fielddata.IndexFieldData;
import org.elasticsearch.index.fielddata.SortedBinaryDocValues;
import java.util.Objects;
/**
* Pseudo randomly generate a score for each {@link LeafScoreFunction#score}.
*/
public class RandomScoreFunction extends ScoreFunction {
private int originalSeed;
private int saltedSeed;
private final IndexFieldData<?> uidFieldData;
/**
* Default constructor. Only useful for constructing as a placeholder, but should not be used for actual scoring.
*/
public RandomScoreFunction() {
super(CombineFunction.MULTIPLY);
uidFieldData = null;
}
/**
* Creates a RandomScoreFunction.
*
* @param seed A seed for randomness
* @param salt A value to salt the seed with, ideally unique to the running node/index
* @param uidFieldData The field data for _uid to use for generating consistent random values for the same id
*/
public RandomScoreFunction(int seed, int salt, IndexFieldData<?> uidFieldData) {
super(CombineFunction.MULTIPLY);
this.originalSeed = seed;
this.saltedSeed = seed ^ salt;
this.uidFieldData = uidFieldData;
if (uidFieldData == null) throw new NullPointerException("uid missing");
}
@Override
public LeafScoreFunction getLeafScoreFunction(LeafReaderContext ctx) {
AtomicFieldData leafData = uidFieldData.load(ctx);
final SortedBinaryDocValues uidByteData = leafData.getBytesValues();
if (uidByteData == null) throw new NullPointerException("failed to get uid byte data");
return new LeafScoreFunction() {
@Override
public double score(int docId, float subQueryScore) {
uidByteData.setDocument(docId);
int hash = StringHelper.murmurhash3_x86_32(uidByteData.valueAt(0), saltedSeed);
return (hash & 0x00FFFFFF) / (float)(1 << 24); // only use the lower 24 bits to construct a float from 0.0-1.0
}
@Override
public Explanation explainScore(int docId, Explanation subQueryScore) {
return Explanation.match(
CombineFunction.toFloat(score(docId, subQueryScore.getValue())),
"random score function (seed: " + originalSeed + ")");
}
};
}
@Override
public boolean needsScores() {
return false;
}
@Override
protected boolean doEquals(ScoreFunction other) {
RandomScoreFunction randomScoreFunction = (RandomScoreFunction) other;
return this.originalSeed == randomScoreFunction.originalSeed &&
this.saltedSeed == randomScoreFunction.saltedSeed;
}
@Override
protected int doHashCode() {
return Objects.hash(originalSeed, saltedSeed);
}
}
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