wikimedia/mediawiki-extensions-CirrusSearch

<?php

namespace CirrusSearch\Search\Rescore;

use CirrusSearch\SearchConfig;
use Elastica\Query\FunctionScore;

/**
 * Builds a script score boost documents on the timestamp field.
 * Can be initialized by config for full text and by special syntax in user query
 */
class PreferRecentFunctionScoreBuilder extends FunctionScoreBuilder {

    /**
     * @var float
     */
    private $halfLife;

    /**
     * @var float
     */
    private $decayPortion;

    /**
     * @param SearchConfig $config
     * @param float $weight
     * @param float $halfLife
     * @param float $decayPortion
     */
    public function __construct( SearchConfig $config, $weight, $halfLife, $decayPortion ) {
        parent::__construct( $config, $weight );
        $this->halfLife = $halfLife;
        $this->decayPortion = $decayPortion;
    }

    public function append( FunctionScore $functionScore ) {
        if ( !( $this->halfLife > 0 && $this->decayPortion > 0 ) ) {
            return;
        }
        // Convert half life for time in days to decay constant for time in milliseconds.
        $decayConstant = log( 2 ) / $this->halfLife / 86400000;
        $parameters = [
            'decayConstant' => $decayConstant,
            'decayPortion' => $this->decayPortion,
            'nonDecayPortion' => 1 - $this->decayPortion,
            'now' => time() * 1000,
        ];

        // e^ct where t is last modified time - now which is negative
        $exponentialDecayExpression = "exp(decayConstant * (doc['timestamp'].value - now))";
        if ( $this->decayPortion !== 1.0 ) {
            $exponentialDecayExpression =
                "$exponentialDecayExpression * decayPortion + nonDecayPortion";
        }
        $functionScore->addScriptScoreFunction( new \Elastica\Script\Script( $exponentialDecayExpression,
            $parameters, 'expression' ), null, $this->weight );
    }
}