add_filter( 'rank_math/snippet/rich_snippet_product_entity', function( $entity ) {
    if ( ! is_product() ) {
        return $entity;
    }

    $product = wc_get_product( get_the_ID() );
    if ( ! $product->is_type( 'variable' ) ) {
        $entity['gtin13'] = get_post_meta( get_the_ID(), 'hwp_var_gtin', true );
        return $entity;
    }

    $variations = $product->get_available_variations();
    if ( ! empty( $variations ) ) {
        $entity['offers'] = [];
        foreach ( $variations as $variation ) {
            $price_valid_until = get_post_meta( $variation['variation_id'], '_sale_price_dates_to', true );
            $entity['offers'][] = [
                '@type'           => 'Offer',
                'description'     => strip_tags( $variation['variation_description'] ),
                'price'           => $variation['display_price'],
                'priceCurrency'   => get_woocommerce_currency(),
                'availability'    => $variation['is_in_stock'] ? 'https://schema.org/InStock' : 'https://schema.org/OutOfStock',
                'itemCondition'   => 'NewCondition',
                'priceValidUntil' => $price_valid_until ? date_i18n( 'Y-m-d', $price_valid_until ) : '2025-12-31',
                'url'             => $product->get_permalink(),
                'sku'             => get_post_meta($variation['variation_id'],'variable_sku', true ),
            ];
        }
    }

    return $entity;
} );