From 83d6ffd7154e0711b340791b3c8d6daca8094c46 Mon Sep 17 00:00:00 2001
From: Matthew Berryman <matthew@acrossthecloud.net>
Date: Sun, 28 Apr 2024 00:04:36 +0930
Subject: [PATCH] fix(isVAT): improved ABN (AU VAT) validation (#2343)

---
 src/lib/isVAT.js        | 18 +++++++++++++++++-
 test/validators.test.js | 18 ++++++++++++++++--
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/src/lib/isVAT.js b/src/lib/isVAT.js
index a8e2611b6..50fcf52e0 100644
--- a/src/lib/isVAT.js
+++ b/src/lib/isVAT.js
@@ -1,6 +1,22 @@
 import assertString from './util/assertString';
 import * as algorithms from './util/algorithms';
 
+const AU = (str) => {
+  const match = str.match(/^(AU)?(\d{11})$/);
+  if (!match) {
+    return false;
+  }
+  // @see {@link https://abr.business.gov.au/Help/AbnFormat}
+  const weights = [10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19];
+  str = str.replace(/^AU/, '');
+  const ABN = (parseInt(str.slice(0, 1), 10) - 1).toString() + str.slice(1);
+  let total = 0;
+  for (let i = 0; i < 11; i++) {
+    total += weights[i] * ABN.charAt(i);
+  }
+  return (total !== 0 && total % 89 === 0);
+};
+
 const CH = (str) => {
   // @see {@link https://www.ech.ch/de/ech/ech-0097/5.2.0}
   const hasValidCheckNumber = (digits) => {
@@ -68,7 +84,7 @@ export const vatMatchers = {
    */
   AL: str => /^(AL)?\w{9}[A-Z]$/.test(str),
   MK: str => /^(MK)?\d{13}$/.test(str),
-  AU: str => /^(AU)?\d{11}$/.test(str),
+  AU,
   BY: str => /^(УНП )?\d{9}$/.test(str),
   CA: str => /^(CA)?\d{9}$/.test(str),
   IS: str => /^(IS)?\d{5,6}$/.test(str),
diff --git a/test/validators.test.js b/test/validators.test.js
index 8462c0f1d..3928a1c5c 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -14105,10 +14105,24 @@ describe('Validators', () => {
       validator: 'isVAT',
       args: ['AU'],
       valid: [
+        'AU53004085616',
+        '53004085616',
+        'AU65613309809',
+        '65613309809',
+        'AU34118972998',
+        '34118972998',
+      ],
+      invalid: [
+        'AU65613309808',
+        '65613309808',
+        'AU55613309809',
+        '55613309809',
+        'AU65613319809',
+        '65613319809',
+        'AU34117972998',
+        '34117972998',
         'AU12345678901',
         '12345678901',
-      ],
-      invalid: [
         'AU 12345678901',
         '1234567890',
       ],