/**
  * Get Screenshot URL for Call to Action preview. If local environment show template thumbnail.
  *
  * @param INT $cta_id id if of call to action
  * @param INT $vid id of variation belonging to call to action
  *
  * @return STRING url of preview
  */
 public static function get_screenshot_url($cta_id, $vid = null)
 {
     if ($vid === null) {
         $vid = CTA_Variations::get_current_variation_id();
     }
     $template = CTA_Variations::get_current_template($cta_id, $vid);
     if (in_array($_SERVER['REMOTE_ADDR'], array('127.0.0.1', '::1'))) {
         if (file_exists(WP_CTA_UPLOADS_URLPATH . 'templates/' . $template . '/thumbnail.png')) {
             $screenshot = WP_CTA_UPLOADS_URLPATH . 'templates/' . $template . '/thumbnail.png';
         } else {
             $screenshot = WP_CTA_URLPATH . 'templates/' . $template . '/thumbnail.png';
         }
     } else {
         $screenshot = 'http://s.wordpress.com/mshots/v1/' . urlencode(esc_url($permalink)) . '?w=140';
     }
     return $screenshot;
 }