LemonStand AJAX Handler for MailChimp function

gistfile1.php

function process_mailing_list($controller)
{
  if (post('mailinglist_signup')) {
    $url = "https://us2.api.mailchimp.com/1.2/?output=php&method=listSubscribe";
    
    $data = Shop_CheckoutData::get_billing_info();
    $country = Shop_Country::create()->find($data->country);
    $state = Shop_CountryState::create()->find($data->state);
    
    $fields = array(
      'FNAME' => $data->first_name,
      'LNAME' => $data->last_name,
      'FORM_LOCAT' => 'rt-reg',
      'STREET' => $data->street_address,
      'CITY' => $data->city,
      'STATE' => $state->name,
      'ZIP' => $data->zip,
      'COUNTRY' => $country->name
    );
    $postdata = http_build_query(
      array(
        'apikey' => '',
        'id' => '',
        'email_address' => $data->email,
        'merge_vars' => $fields,
        'email_type' => 'html',
        'double_option' => true,
        'update_existing' => true
      )
    );
    $options = array(
      'http' => array(
        'method' => 'POST',
        'content' => $postdata,
        'header' => 'Content-Type: application/x-www-form-urlencoded'
      )
    );
    $context = stream_context_create( $options );
    $return = file_get_contents( $url, false, $context );
  }
  $controller->action();
}