4
	 *
	 * @param number $product_per_page Products per page.
	 * @return int[] Products ids.
	 */
	private function get_related_products_ids( $product_per_page = 5 ): array {
		global $post;

		$product = wc_get_product( $post->ID );

		if ( ! $product instanceof \WC_Product ) {
			return array();
		}

		$related_products_ids = wc_get_related_products( $product->get_id(), $product_per_page, $product->get_upsell_ids() );
		if ( ! empty( $related_products_ids ) ) {
			// Prime caches to reduce future queries.
			_prime_post_caches( $related_products_ids );

			$related_products = array_filter( array_map( 'wc_get_product', $related_products_ids ), 'wc_products_array_filter_visible' );
			$related_products = wc_products_array_orderby( $related_products, 'rand', 'desc' );
			/** @var \WC_Product[] $related_products */ // phpcs:ignore Generic.Commenting.DocComment.MissingShort

			// Prime caches to reduce future queries.
			_prime_post_caches( array_filter( array_map( fn( $product ) => (int) $product->get_image_id(), $related_products ) ) );

			$related_products_ids = array_map( fn( $product ) => $product->get_id(), $related_products );
		}

		return $related_products_ids;
	}
}