Add Belgian OGM-VCS

Closes #487

Author: cedk

stdnum/be/ogm_vcs.py

@@ -0,0 +1,81 @@
+# ogm_vcs.py - functions for handling Belgian OGM-VCS
+# coding: utf-8
+#
+# Copyright (C) 2025 Cédric Krier
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301 USA
+
+"""Belgian OGM-VCS.
+
+The OGM-VCS is used in bank transfer as structured communication.
+
+* https://febelfin.be/en/publications/2023/febelfin-banking-standards-for-online-banking
+
+>>> validate('+++010/8068/17183+++')
+'010806817183'
+>>> validate('010/8068/17180')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
+>>> format('010806817183')
+'010/8068/17183'
+>>> calc_check_digits('0108068171')
+'83'
+"""
+
+from __future__ import annotations
+
+from stdnum.exceptions import *
+from stdnum.util import clean, isdigits
+
+
+def compact(number: str) -> str:
+    """Convert the number to the minimal representation. This strips the number
+    of any invalid separators and removes surrounding whitespace."""
+    return clean(number, ' +/').strip()
+
+
+def calc_check_digits(number: str) -> str:
+    """Calculate the check digit that should be added."""
+    number = compact(number)
+    return '%02d' % ((int(number[:10]) % 97) or 97)
+
+
+def validate(number: str) -> str:
+    """Check if the number is a valid OGM-VCS."""
+    number = compact(number)
+    if not isdigits(number) or int(number) <= 0:
+        raise InvalidFormat()
+    if len(number) != 12:
+        raise InvalidLength()
+    if calc_check_digits(number) != number[-2:]:
+        raise InvalidChecksum()
+    return number
+
+
+def is_valid(number: str) -> bool:
+    """Check if the number is a valid VAT number."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False
+
+
+def format(number: str) -> str:
+    """Format the number provided for output."""
+    number = compact(number)
+    number = number.rjust(12, '0')
+    return f'{number[:3]}/{number[3:7]}/{number[7:]}'