onomy to get the defining term id for.
	 * @param array                 $term_ids_by_slug_cache A term ids by slug as generated by get_term_ids_by_slug_cache.
	 * @return int|null The term id, or null if there's no defining id for that taxonomy in that variation.
	 */
	private function get_variation_definition_term_id( \WC_Product_Variation $variation, string $taxonomy, array $term_ids_by_slug_cache ) {
		$variation_attributes = $variation->get_attributes();
		$term_slug            = ArrayUtil::get_value_or_default( $variation_attributes, $taxonomy );
		if ( $term_slug ) {
			return $term_ids_by_slug_cache[ $taxonomy ][ $term_slug ];
		} else {
			return null;
		}
	}

	/**
	 * Get the variations of a given variable product.
	 *
	 * @param \WC_Product_Variable $product The product to get the variations for.
	 * @return array An array of WC_Product_Variation objects.
	 */
	private function get_variations_of( \WC_Product_Variable $product ) {
		$variation_ids = $product->get_children();
		return array_map(
			function( $id ) {
				return WC()->call_function( 'wc_get_product', $id );
			},
			$variation_ids
		);
	}

	/**
	 * Check if a given product is a variable product.
	 *
	 * @param \WC_Product $product The product to check.
	 * @return bool True if it's a variable product, false otherwise.
	 */
	private function is_variable_product( \WC_Product $product ) {
		return is_a( $product, \WC_Product_Variable::class );
	}

	/**
	 * Check if a given product is a variation.
	 *
	 * @param \WC_Product $product The product to check.
	 * @return bool True if it's a variation, false otherwise.
	 */
	private function is_variation( \WC_Product $product ) {
		return is_a( $product, \WC_Product_Variation::class );
	}

	/**
	 * Return the list of taxonomies used for variations on a product together with
	 * the associated term ids, with the following format:
	 *
	 * [
	 *   'taxonomy_name' =>
	 *   [
	 *     'term_ids' => [id, id, ...],
	 *     'used_for_variations' => true|false
	 *   ], ...
	 * ]
	 *
	 * @param \WC_Product $product The product to get the attribute taxonomies for.
	 * @return array Information about the attribute taxonomies of the product.
	 */
	private function get_attribute_taxonomies( \WC_Product $product ) {
		$product_attributes = $product->get_attributes();
		$result             = array();
		foreach ( $product_attributes as $taxonomy_name => $attribute_data ) {
			if ( ! $attribute_data->get_id() ) {
				// Custom product attribute, not suitable for attribute-based filtering.
				continue;
			}

			$result[ $taxonomy_name ] = array(
				'term_ids'            => $attribute_data->get_options(),
				'used_for_variations' => $attribute_data->get_variation(),
			);
		}

		return $result;
	}

	/**
	 * Insert one entry in the lookup table.
	 *
	 * @param int    $product_id The product id.
	 * @param int    $product_or_parent_id The product id for non-variable products, the main/parent product id for variations.
	 * @param string $taxonomy Taxonomy name.
	 * @param int    $term_id Term id.
	 * @param bool   $is_variation_attribute True if the taxonomy corresponds to an attribute used to define variations.
	 * @param bool   $has_stock True if the product is in stock.
	 */
	private function insert_lookup_table_data( int $product_id, int $product_or_parent_id, string $taxonomy, int $term_id, bool $is_variation_attribute, bool $has_stock ) {
		global $wpdb;

		// phpcs:disable WordPress.DB.PreparedSQL.NotPrepared
		$wpdb->query(
			$wpdb->prepare(
				'INSERT INTO ' . $this->lookup_table_name . ' (
					  product_id,
					  product_or_parent_id,
					  taxonomy,
					  term_id,
					  is_variation_attribute,
					  in_stock)
					VALUES
					  ( %d, %d, %s, %d, %d, %d )',
				$product_id,
				$product_or_parent_id,
				$taxonomy,
				$term_id,
				$is_variation_attribute ? 1 : 0,
				$has_stock ? 1 : 0
			)
		);
		// phpcs:enable WordPress.DB.PreparedSQL.NotPrepared
	}

	/**
	 * Tells if a lookup table regeneration is currently in progress.
	 *
	 * @return bool True if a lookup table regeneration is already in progress.
	 */
	public function regeneration_is_in_progress() {
		return 'yes' === get_option( 'woocommerce_attribute_lookup_regeneration_in_progress', null );
	}

	/**
	 * Set a permanent flag (via option) indicating that the lookup table regeneration is in process.
	 */
	public function set_regeneration_in_progress_flag() {
		update_option( 'woocommerce_attribute_lookup_regeneration_in_progress', 'yes' );
	}

	/**
	 * Remove the flag indicating that the lookup table regeneration is in process.
	 */
	public function unset_regeneration_in_progress_flag() {
		delete_option( 'woocommerce_attribute_lookup_regeneration_in_progress' );
	}
}