public static function email_header($email_heading = '')
 {
     $file = 'email_header.html';
     if (file_exists(STYLESHEETPATH . '/emails/' . $file)) {
         // $header_template_path = get_stylesheet_directory() . '/emails/'. $file;
         $header_template_path = STYLESHEETPATH . '/emails/' . $file;
         $header_template_url = get_stylesheet_directory_uri() . '/emails/' . $file;
     } else {
         $header_template_path = WP_EMAIL_TEMPLATE_DIR . '/emails/' . $file;
         $header_template_url = WP_EMAIL_TEMPLATE_URL . '/emails/' . $file;
     }
     $template_html = file_get_contents($header_template_path);
     if ($template_html == false) {
         $ch = curl_init($header_template_url);
         curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
         curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
         $template_html = curl_exec($ch);
         curl_close($ch);
     }
     $template_html = WP_Email_Template_Functions::replace_shortcode_header($template_html, $email_heading);
     return $template_html;
 }