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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 com.carrotsearch.hppc.BitMixer;
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.io.IOException;
import java.util.Objects;
/**
* Pseudo randomly generate a score for each {@link LeafScoreFunction#score}.
*/
public class RandomScoreFunction extends ScoreFunction {
private final int originalSeed;
private final int saltedSeed;
private final IndexFieldData fieldData;
/**
* 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 = BitMixer.mix(seed, salt);
this.fieldData = uidFieldData;
}
@Override
public LeafScoreFunction getLeafScoreFunction(LeafReaderContext ctx) {
final SortedBinaryDocValues values;
if (fieldData != null) {
AtomicFieldData leafData = fieldData.load(ctx);
values = leafData.getBytesValues();
if (values == null) throw new NullPointerException("failed to get fielddata");
} else {
values = null;
}
return new LeafScoreFunction() {
@Override
public double score(int docId, float subQueryScore) throws IOException {
int hash;
if (values == null) {
hash = BitMixer.mix(ctx.docBase + docId, saltedSeed);
} else if (values.advanceExact(docId)) {
hash = StringHelper.murmurhash3_x86_32(values.nextValue(), saltedSeed);
} else {
// field has no value
hash = 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) throws IOException {
String field = fieldData == null ? null : fieldData.getFieldName();
return Explanation.match(
(float) score(docId, subQueryScore.getValue().floatValue()),
"random score function (seed: " + originalSeed + ", field: " + field + ")");
}
};
}
@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);
}
}