protected function attachSku(array &$product)
    {
        if (empty($product)) {
            return $product;
        }

        $product['default_field_values'] = array();
        $codes = (array) $this->sku->getList(array('product_id' => $product['product_id']));

        foreach ($codes as $code) {

            if ($code['combination_id'] === '') {
                $product['sku'] = $code['sku'];
                $product['price'] = $code['price'];
                $product['stock'] = $code['stock'];
                continue;
            }

            $product['combination'][$code['combination_id']] = $code;

            if (!empty($code['is_default'])) {
                $product['default_field_values'] = $code['fields'];
            }
        }

        return $product;
    }