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There is a newer version: 8.14.0

/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.action.search;

import org.apache.lucene.search.Scorable;
import org.apache.lucene.search.ScoreMode;
import org.apache.lucene.search.SimpleCollector;

import java.io.IOException;

/**
 * A collector that computes the maximum score.
 */
public class MaxScoreCollector extends SimpleCollector {

    private Scorable scorer;
    private float maxScore = Float.NEGATIVE_INFINITY;
    private boolean hasHits = false;

    @Override
    public void setScorer(Scorable scorer) {
        this.scorer = scorer;
    }

    @Override
    public ScoreMode scoreMode() {
        // Could be TOP_SCORES but it is always used in a MultiCollector anyway, so this saves some wrapping.
        return ScoreMode.COMPLETE;
    }

    @Override
    public void collect(int doc) throws IOException {
        hasHits = true;
        maxScore = Math.max(maxScore, scorer.score());
    }

    /**
     * Get the maximum score. This returns {@link Float#NaN} if no hits were
     * collected.
     */
    public float getMaxScore() {
        return hasHits ? maxScore : Float.NaN;
    }

}