/**
  * Output a pricing table
  *
  * * product_id/product_sku - id or sku of product.  Defaults to current product, if any
  *
  * Usage:
  * [wc_measurement_price_calculator_pricing_table]
  *
  * @param array $atts associative array of shortcode parameters
  */
 public static function output($atts)
 {
     global $product, $wpdb;
     extract(shortcode_atts(array('product_id' => '', 'product_sku' => ''), $atts));
     // product by sku?
     if ($product_sku) {
         $product_id = $wpdb->get_var($wpdb->prepare("SELECT post_id FROM {$wpdb->postmeta} WHERE meta_key='_sku' AND meta_value=%s LIMIT 1", $product_sku));
     }
     // product by id?
     if ($product_id) {
         $product = wc_get_product($product_id);
     }
     // product ?
     if (!$product) {
         return;
     }
     // pricing rules?
     $settings = new WC_Price_Calculator_Settings($product);
     if (!$settings->pricing_rules_enabled() || !$settings->has_pricing_rules()) {
         return;
     }
     // the countdown element with a unique identifier to allow multiple countdowns on the same page, and common class for ease of styling
     echo self::get_pricing_rules_table($settings->get_pricing_rules($settings->get_pricing_unit()), $settings);
 }