Add boosting to ElasticPress queries. THIS IS NOT COMPLETE YET.

elasticpress-custom-query-boosting.php

<?php
/**
 * Plugin Name: ElasticPress - Custom Query Boosting
 * Description: Add Boosting query to ElasticPress
 * Version:     1.0.0
 * Author:      10up | Felipe Elia
 * Author URI:  https://10up.com/
 * Text Domain: elasticpress-custom-query-boosting
 * Domain Path: /languages
 *
 * @package ElasticPressCustomQueryBoosting
 */

namespace ElasticPressCustomQueryBoosting;

/**
 * Adds 'boosting' to the Elasticsearch query
 *
 * @param array     $formatted_args Formatted Elasticsearch query.
 * @param array     $args           WP_Query arguments
 * @param \WP_Query $query          WP_Query object
 * @return array
 */
function add_boosting_query( $formatted_args, $args, $query ) {
	if ( ! $query->is_main_query() ) {
		return $formatted_args;
	}

	if ( ! isset( $formatted_args['query'] ) ) {
		$formatted_args['query'] = [];
	}

	$boosting = [
		'positive'       => [
			'term' => [
				'meta._stock_status.value' => 'instock',
			],
		],
		'negative'       => [
			'term' => [
				'meta._stock_status.value' => 'outofstock',
			],
		],
		'negative_boost' => 0.05,
	];

	$formatted_args['query']['boosting'] = $boosting;

	return $formatted_args;
}
add_filter( 'ep_post_formatted_args', __NAMESPACE__ . '\\add_boosting_query', 10, 3 );