From b927e1eaaa70c5bc0ede1a1736eafb37c2831fe1 Mon Sep 17 00:00:00 2001
From: Benjamin Dauvergne <bdauvergne@entrouvert.com>
Date: Tue, 23 Jul 2019 17:40:14 +0200
Subject: [PATCH] template filter for Luhn algorithm (#35013)

---
 tests/test_templates.py           | 19 +++++++++++++++++++
 wcs/qommon/templatetags/qommon.py | 30 ++++++++++++++++++++++++++----
 2 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/tests/test_templates.py b/tests/test_templates.py
index 18f0ea65..31dc78b6 100644
--- a/tests/test_templates.py
+++ b/tests/test_templates.py
@@ -522,3 +522,22 @@ def test_reproj():
     lazy_formdata = LazyFormData(MockFormData())
     tmpl = Template('{% with form_geoloc_base|reproj:"EPSG:3946" as c %}{{c.0}}/{{c.1}}{% endwith %}')
     assert tmpl.render(CompatibilityNamesDict({'form': lazy_formdata})) == '1625337.15483/5422836.71627'
+
+def test_luhn():
+    # EO Siret
+    tmpl = Template('{% if  "44317013900036"|luhn %}yes{% endif %}')
+    assert tmpl.render() == 'yes'
+    for i in range(10):
+        if i == 6:
+            continue
+        tmpl = Template('{% if  "4431701390003' + str(i) + '"|luhn %}yes{% endif %}')
+        assert tmpl.render() == ''
+
+    # EO Siren
+    tmpl = Template('{% if  "443170139"|luhn %}yes{% endif %}')
+    assert tmpl.render() == 'yes'
+    for i in range(10):
+        if i == 9:
+            continue
+        tmpl = Template('{% if  "44317013' + str(i) + '"|luhn %}yes{% endif %}')
+        assert tmpl.render() == ''
diff --git a/wcs/qommon/templatetags/qommon.py b/wcs/qommon/templatetags/qommon.py
index 5178392d..d7e5f92a 100644
--- a/wcs/qommon/templatetags/qommon.py
+++ b/wcs/qommon/templatetags/qommon.py
@@ -20,6 +20,7 @@ from decimal import InvalidOperation as DecimalInvalidOperation
 from decimal import DivisionByZero as DecimalDivisionByZero
 import hashlib
 import math
+import re
 import string
 import random
 
@@ -28,7 +29,7 @@ from pyproj import Geod
 
 from django import template
 from django.template import defaultfilters
-from django.utils import dateparse
+from django.utils import dateparse, six
 from django.utils.safestring import mark_safe
 from wcs.qommon import evalutils
 from wcs.qommon import tokens
@@ -44,13 +45,13 @@ def get(mapping, key):
 
 @register.filter
 def startswith(string, substring):
-    return string and unicode(string).startswith(unicode(substring))
+    return string and six.text_type(string).startswith(six.text_type(substring))
 
 @register.filter
 def split(string, separator=' '):
     if not string:
         return []
-    return unicode(string).split(unicode(separator))
+    return six.text_type(string).split(six.text_type(separator))
 
 @register.filter
 def parse_date(date_string):
@@ -306,7 +307,7 @@ def token_alphanum(length=4):
 
 @register.filter
 def token_check(token1, token2):
-    return unicode(token1).strip().upper() == unicode(token2).strip().upper()
+    return six.text_type(token1).strip().upper() == six.text_type(token2).strip().upper()
 
 
 def get_latlon(obj):
@@ -348,3 +349,24 @@ def reproj(coords, projection_name):
     proj = pyproj.Proj(init='EPSG:4326')
     target_proj = pyproj.Proj(init=projection_name)
     return pyproj.transform(proj, target_proj, coords['lon'], coords['lat'])
+
+@register.filter
+def luhn(value):
+    '''Verify Luhn checksum on a string representing a number'''
+    if not value:
+        return False
+    string_value = six.text_type(value)
+    string_value = string_value.strip()
+    string_value = re.sub(r'\s', '', string_value)
+    if not string_value.isdigit():
+        return False
+
+    # take all digits couting from the right, double value for digits pair
+    # index (counting from 1), if double has 2 digits take their sum
+    checksum = 0
+    for i, x in enumerate(reversed(string_value)):
+        if i % 2 == 0:
+            checksum += int(x)
+        else:
+            checksum += sum(int(y) for y in str(2 * int(x)))
+    return checksum % 10 == 0
-- 
2.22.0