[FIX] base_vat: new dutch vat number verification

Steps to reproduce:
- install contacts and vat number validation
- setup your company country to "Netherlands"
- go to contacts > add a company > try to add a dutch vat number
 (NL264077921B03)

Previous behavior:
Proper vat numbers are considered unvalid and raise a ValidationError

Current behavior:
Specific check added for dutch vat numbers

Related:
http://kleineondernemer.nl/index.php/nieuw-btw-identificatienummer-vanaf-1-januari-2020-voor-eenmanszaken
https://business.gov.nl/regulation/using-checking-vat-numbers/
http://www.pruefziffernberechnung.de/U/USt-IdNr.shtml

opw-2166380

closes odoo/odoo#43081

X-original-commit: b7a82684a311d736dfffd822c2fce8896104b96d
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>
Co-authored-by: Nicolas Martinelli <nim@odoo.com>

addons/base_vat/models/res_partner.py

@@ -294,6 +294,61 @@ class ResPartner(models.Model):
         # Valid format and valid date
         return True
 
+    # Netherlands VAT verification
+    __check_vat_nl_re = re.compile("(?:NL)?[0-9A-Z+*]{10}[0-9]{2}")
+
+    def check_vat_nl(self, vat):
+        """
+        Temporary Netherlands VAT validation to support the new format introduced in January 2020,
+        until upstream is fixed.
+
+        Algorithm detail: http://kleineondernemer.nl/index.php/nieuw-btw-identificatienummer-vanaf-1-januari-2020-voor-eenmanszaken
+
+        TODO: remove when fixed upstream
+        """
+
+        try:
+            from stdnum.util import clean
+            from stdnum.nl.bsn import checksum
+        except ImportError:
+            return True
+
+        vat = clean(vat, ' -.').upper().strip()
+
+        if not (len(vat) == 14):
+            return False
+
+        # Check the format
+        match = self.__check_vat_nl_re.match(vat)
+        if not match:
+            return False
+
+        # Match letters to integers
+        char_to_int = {k: str(ord(k) - 55) for k in string.ascii_uppercase}
+        char_to_int['+'] = '36'
+        char_to_int['*'] = '37'
+
+        # Remove the prefix
+        vat = vat[2:]
+
+        # 2 possible checks:
+        # - For natural persons
+        # - For non-natural persons and combinations of natural persons (company)
+
+        # Natural person => mod97 full checksum
+        check_val_natural = '2321'
+        for x in vat:
+            check_val_natural += x if x.isdigit() else char_to_int[x]
+        if int(check_val_natural) % 97 == 1:
+            return True
+
+        # Company => weighted(9->2) mod11 on bsn
+        vat = vat[:-3]
+        if vat.isdigit() and checksum(vat) == 0:
+            return True
+
+        return False
+
     # Norway VAT validation, contributed by Rolv Råen (adEgo) <rora@adego.no>
     # Support for MVA suffix contributed by Bringsvor Consulting AS (bringsvor@bringsvor.com)
     def check_vat_no(self, vat):
@@ -418,3 +473,4 @@ class ResPartner(models.Model):
         if values.get('vat'):
             values['vat'] = self._fix_vat_number(values['vat'])
         return super(ResPartner, self).write(values)
+