fix(isVAT): corrected validation for Swiss (CH) locale (#2203)

* correct isVAT regex for CH

* use checkdigit for swiss isvat

* allow space as number separator, edit test cases

* fix: correct test-case, edit comment

* extract vat matcher for Switzerland (CH)
- adjust number separation rule
- edit comments in test

Author: jimmyorpheus

src/lib/isVAT.js

@@ -1,6 +1,21 @@
 import assertString from './util/assertString';
 import * as algorithms from './util/algorithms';
 
+const CH = (str) => {
+  // @see {@link https://www.ech.ch/de/ech/ech-0097/5.2.0}
+  const hasValidCheckNumber = (digits) => {
+    const lastDigit = digits.pop(); // used as check number
+    const weights = [5, 4, 3, 2, 7, 6, 5, 4];
+    const calculatedCheckNumber = (11 - (digits.reduce((acc, el, idx) =>
+      acc + (el * weights[idx]), 0) % 11)) % 11;
+
+    return lastDigit === calculatedCheckNumber;
+  };
+
+  // @see {@link https://www.estv.admin.ch/estv/de/home/mehrwertsteuer/uid/mwst-uid-nummer.html}
+  return /^(CHE[- ]?)?(\d{9}|(\d{3}\.\d{3}\.\d{3})|(\d{3} \d{3} \d{3})) ?(TVA|MWST|IVA)?$/.test(str) && hasValidCheckNumber((str.match(/\d/g).map(el => +el)));
+};
+
 const PT = (str) => {
   const match = str.match(/^(PT)?(\d{9})$/);
   if (!match) {
@@ -69,7 +84,7 @@ export const vatMatchers = {
   SM: str => /^(SM)?\d{5}$/.test(str),
   SA: str => /^(SA)?\d{15}$/.test(str),
   RS: str => /^(RS)?\d{9}$/.test(str),
-  CH: str => /^(CH)?(\d{6}|\d{9}|(\d{3}.\d{3})|(\d{3}.\d{3}.\d{3}))(TVA|MWST|IVA)$/.test(str),
+  CH,
   TR: str => /^(TR)?\d{10}$/.test(str),
   UA: str => /^(UA)?\d{12}$/.test(str),
   GB: str => /^GB((\d{3} \d{4} ([0-8][0-9]|9[0-6]))|(\d{9} \d{3})|(((GD[0-4])|(HA[5-9]))[0-9]{2}))$/.test(str),

test/validators.test.js

@@ -13891,18 +13891,30 @@ describe('Validators', () => {
       validator: 'isVAT',
       args: ['CH'],
       valid: [
-        'CH123456TVA',
-        '123456TVA',
-        'CH123456789MWST',
-        '123456789MWST',
-        'CH123.456IVA',
-        '123.456IVA',
-        'CH123.456.789TVA',
-        '123.456.789TVA',
-      ],
-      invalid: [
-        'CH 123456',
-        '12345',
+        // strictly valid
+        'CHE-116.281.710 MWST',
+        'CHE-116.281.710 IVA',
+        'CHE-116.281.710 TVA',
+        // loosely valid presentation variants
+        'CHE 116 281 710 IVA', // all separators are spaces
+        'CHE-191.398.369MWST', // no space before suffix
+        'CHE-116281710 MWST', // no number separators
+        'CHE-116281710MWST', // no number separators and no space before suffix
+        'CHE105854263MWST', // no separators
+        'CHE-116.285.524', // no suffix (vat abbreviation)
+        'CHE116281710', // no suffix and separators
+        '116.281.710 TVA', // no prefix (CHE, ISO-3166-1 Alpha-3)
+        '116281710MWST', // no prefix and separators
+        '100.218.485', // no prefix and suffix
+        '123456788', // no prefix, separators and suffix
+      ],
+      invalid: [
+        'CH-116.281.710 MWST', // invalid prefix (should be CHE)
+        'CHE-116.281 MWST', // invalid number of digits (should be 9)
+        'CHE-123.456.789 MWST', // invalid last digit (should match the calculated check-number 8)
+        'CHE-123.356.780 MWST', // invalid check-number (there are no swiss UIDs with the calculated check number 10)
+        'CH-116.281.710 VAT', // invalid suffix (should be MWST, IVA or TVA)
+        'CHE-116/281/710 IVA', // invalid number separators (should be all dots or all spaces)
       ],
     });
     test({