From 61f1a24381a6078a56e2c31bec190a415bb2d0d0 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           | 22 +++++++++++++++++++++
 wcs/qommon/templatetags/qommon.py | 32 +++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/tests/test_templates.py b/tests/test_templates.py
index 18f0ea65..e9ca0a3a 100644
--- a/tests/test_templates.py
+++ b/tests/test_templates.py
@@ -522,3 +522,25 @@ 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"|is_valid_siret%}yes{% endif %}')
+    assert tmpl.render() == 'yes'
+    # with spaces
+    tmpl = Template('{% if  " 443 170\t139 00 036 "|is_valid_siret %}yes{% endif %}')
+    assert tmpl.render() == 'yes'
+    for i in range(10):
+        if i == 6:
+            continue
+        tmpl = Template('{% if  "4431701390003' + str(i) + '"|is_valid_siret %}yes{% endif %}')
+        assert tmpl.render() == ''
+
+    # EO Siren
+    tmpl = Template('{% if  "443170139"|is_valid_siren %}yes{% endif %}')
+    assert tmpl.render() == 'yes'
+    for i in range(10):
+        if i == 9:
+            continue
+        tmpl = Template('{% if  "44317013' + str(i) + '"|is_valid_siren %}yes{% endif %}')
+        assert tmpl.render() == ''
diff --git a/wcs/qommon/templatetags/qommon.py b/wcs/qommon/templatetags/qommon.py
index 5178392d..31e0e0b0 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
 
@@ -348,3 +349,34 @@ 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'])
+
+def is_valid_luhn(value):
+    '''Verify Luhn checksum on a string representing a number'''
+    if not value:
+        return False
+    string_value = unicode(value)
+    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
+
+@register.filter
+def is_valid_siren(value):
+    return is_valid_luhn(value)
+
+@register.filter
+def is_valid_siret(value):
+    return is_valid_luhn(value)
+
+@register.filter
+def is_valid_cb(value):
+    return is_valid_luhn(value)
-- 
2.22.0