How to unobtrusively add new Validation methods to Magento checkout? - ajax

Question

I want to prevent customers entering PO Boxes into the shipping address for selected Shipping Methods (UPS specifically in this case). I could override js/prototype/validation.js to insert a new validation pattern, but I don't want to fork such a key file.
Is there a mechanism to unobtrusively validate the customer's shipping address AFTER they select a shipping method via Javascript without overriding core files?
I see that Validation.add is used inside the validation.js, so it may be possible to add a new validation method outside of the core file?
The regex that I want to apply is:
\b([P|p](OST|ost)?\.?\s?[O|o|0](ffice|FFICE)?\.?\s)?([B|b][O|o|0][X|x])\s(\d+)
If the validation cannot be performed elegantly in the JS, I would be interested in an Observer on the controller_action_predispatch_onepage_saveShippingMethod that inspects the data and performs an Ajax redirect back to the shipping address form if necessary.

Answer 1

The library used is Really Easy Field Validation and that page does explain how to extend it. I guess you will need something like this:
Validation.add('address', 'Error message text', {
pattern : /\b([P|p](OST|ost)?\.?\s?[O|o|0](ffice|FFICE)?\.?\s)?([B|b][O|o|0][X|x])\s(\d+)/
});

Answer 2

As a brief look into it without debugging the checkout
# Unfortunately Magento 1.3.2.3 - Find real postcode from debugging checkout
public function saveShippingAction()
{
$this->_expireAjax();
if ($this->getRequest()->isPost()) {
$data = $this->getRequest()->getPost('shipping', array());
$customerAddressId = $this->getRequest()->getPost('shipping_address_id', false);
$result = $this->getOnepage()->saveShipping($data, $customerAddressId);
$preg_search = '\b([P|p](OST|ost)?\.?\s?[O|o|0](ffice|FFICE)?\.?\s)?([B|b][O|o|0][X|x])\s(\d+)';
$address = $this->getQuote()->getShippingAddress(); #find real postcode
if(preg_match($preg_search, $address['postcode']){
$result = array(
'error' => 1,
'message' => Mage::helper('checkout')->__('Invalid PO Box postcode');
);
}
else{
if (!isset($result['error'])) {
$result['goto_section'] = 'shipping_method';
$result['update_section'] = array(
'name' => 'shipping-method',
'html' => $this->_getShippingMethodsHtml()
);
}
}
$this->getResponse()->setBody(Zend_Json::encode($result));
}
}