EU VAT with DNI field : group assignment and free shipping

[Mooon]

EU VAT has been quite discussed here but my client need is a mix of the threads I've seen. Prestashop 1.4 may bring solutions but obviously, theme and plugins have been bought for 1.3.7 and budget is empty.

Here is the need :
[*] The website is b2b : only pro customers
[*] there is a minimum amount for order
[*] we want customers that enter EU VAT Number (in DNI field) to be VAT free and transport free
[*] customers without DNI filled are charged VAT of the shop country and transport by weight

Here is how I see it :
[*] Customer registering without DNI stays in default group for taxes, and in zone with pay carrier
[*] Customer registering with DNI is assigned to special group only and has only free carrier available
[*] AND
[*] Customer changing DNI in his account have also same effects.

Uf !

FIRST STEP is unlocking the DNI registration based on this EU VAT Thread

In classes classes/validate.php I tried regexp based on a code seen somewhere to validate number form (by the way it's certainly bugged so if you have improvement)

Replace :
if (!preg_match('/((^[A-Z]{1}[0-9]{7}[A-Z0-9]{1}$|^[T]{1}[A-Z0-9]{8}$)|^[0-9]{8}[A-Z]{1}$)/', $dni)) 

By :
if (!preg_match('/^(RO[0-9]{2,10}|GB[0-9]{5}|(ATU|DK|FI|HU|LU|MT|CZ|SI)[0-9]{8}|IE[A-Z0-9]{8}|(DE|BG|EE|EL|LT|BE0|
PT|CZ)[0-9]{9}|CY[0-9]{8}[A-Z]|(ES|GB)[A-Z0-9]{9}|(BE0|PL|SK|CZ)[0-9]{10}|(FR|IT|LV)[0-9]{11}|(LT|SE)[0-9]{12}|
(NL|GB)[A-Z0-9]{12})$/', $dni)) 

Then I tried to assign customer with DNI to a free tax group in authentification.php, based on same thread :

else
{
   if (Tools::getValue('dni') != '')
       $customer->addGroups(array(2));                
   $address->id_customer = intval($customer->id); 

at registration customer goes to the good group, but prices in order doesn't change. I haven't tested yet this solution but it seems to be the same.

SECOND STEP is configuring into admin
- Payment / taxes : two taxes (one at 0), both on the same zones... (delivery zones by weight)
- Shipping : 2 carriers, one with prices by weight and zone, other with weight and 0 price for each zone
- Shipping / carrier : one is tax included other is tax excluded

DNI or not DNI, taxes doesn't show up !

THIRD STEP is making shipping free if DNI filled, based on this :

if (isset($configuration['PS_SHIPPING_FREE_PRICE']) AND $orderTotal >= floatval($configuration

['PS_SHIPPING_FREE_PRICE']) AND floatval($configuration['PS_SHIPPING_FREE_PRICE']) > 0 AND $id_zone==6)
           return $shipping_cost;

I tried to adapt :

if ($orderTotalwithDiscounts >= floatval($free_fees_price) AND floatval($free_fees_price) > 0 AND intval($id_carrier) == 2 AND ((intval($id_zone) == 6 OR intval($id_zone) == 18) && Tools::getValue('dni') != ''))

Doesn't work and I don't have idea on how to get DNI here. I tried to adapt a solution based on address validation :

add anywhere in classes/customer.php

static public function getDni($id_customer)
   {
       $result = Db::getInstance()->getRow('
           SELECT `dni` FROM `'._DB_PREFIX_.'customer`
           WHERE `id_customer` = '.intval($id_customer));
       return isset($result['dni']) ? $result['dni'] : false;
   }   

order.php (root) around l.320

[b]under :[/b]
function displayCarrier()
{
   global $smarty, $cart, $cookie, $defaultCountry, $link;
   $address = new Address
(intval($cart->id_address_delivery));
   $id_zone = Address::getZoneById(intval($address->id));

[b]Add[/b]        
   $dni = Address::getDni($customer->id);

in order-carrier.tpl

[b]Replace[/b]
<input type="radio" name="id_carrier" value="{$carrier.id_carrier|intval}" id="id_carrier{$carrier.id_carrier|
intval}" {if $carrier.id_carrier == $checked || ($checked == 0 && $i == 0) || ($carriers|@sizeof == 1)}
checked="checked"{/if} />

By
{if $carrier.id_carrier=='2'}
                           {if $dni != ''}
                           <input 
type="radio" name="id_carrier" value="{$carrier.id_carrier|intval}" id="id_carrier{$carrier.id_carrier|intval}" {if 
$carrier.id_carrier == $checked || ($checked == 0 && $i == 0) || ($carriers|@sizeof == 1)}checked="checked"{/if} />
                          {else}-
                           {/if}
                       {else}               
    <input type="radio" name="id_carrier" value="{$carrier.id_carrier|intval}" id="id_carrier
{$carrier.id_carrier|intval}" {if $carrier.id_carrier == $checked || ($checked == 0 && $i == 0) || ($carriers|
@sizeof == 1)}checked="checked"{/if} />
                       {/if}

And around l.380

after
$smarty->assign(array(

add
'dni' => $dni, // EU VAT

I have more code and options, but I'd like to debate a little before

So, I know I won't have all the answers (but hope some), but my brain really needs fresh eye to tell me what is wrong.