fix: Luhn generation algorithms and tests (#980)

Co-authored-by: ST-DDT <ST-DDT@gmx.de>

src/modules/helpers/index.ts

@@ -1,4 +1,5 @@
 import type { Faker } from '../..';
+import { luhnCheckValue } from './luhn-check';
 
 /**
  * Module with various helper methods that transform the method input rather than returning values from locales.
@@ -141,30 +142,10 @@ export class Helpers {
   ): string {
     // default values required for calling method without arguments
 
-    // Function calculating the Luhn checksum of a number string
-    const getCheckBit = (number: number[]) => {
-      number.reverse();
-      number = number.map((num, index) => {
-        if (index % 2 === 0) {
-          num *= 2;
-          if (num > 9) {
-            num -= 9;
-          }
-        }
-        return num;
-      });
-      const sum = number.reduce((prev, curr) => prev + curr);
-      return sum % 10;
-    };
-
     string = this.regexpStyleStringParse(string); // replace [4-9] with a random number in range etc...
     string = this.replaceSymbolWithNumber(string, symbol); // replace ### with random numbers
 
-    const numberList = string
-      .replace(/\D/g, '')
-      .split('')
-      .map((num) => parseInt(num));
-    const checkNum = getCheckBit(numberList);
+    const checkNum = luhnCheckValue(string);
     return string.replace('L', String(checkNum));
   }
 

src/modules/helpers/luhn-check.ts

@@ -0,0 +1,42 @@
+/**
+ * Checks that the given string passes the luhn algorithm.
+ *
+ * @param str The string to validate.
+ */
+export function luhnCheck(str: string): boolean {
+  return luhnChecksum(str) === 0;
+}
+
+/**
+ * Calculates the luhn check value for the given string.
+ *
+ * @param str The string to calculate the check value for.
+ * May contain the `L` placeholder at the end.
+ */
+export function luhnCheckValue(str: string): number {
+  const checksum = luhnChecksum(str.replace(/L?$/, '0'));
+  return checksum === 0 ? 0 : 10 - checksum;
+}
+
+/**
+ * Calculates the luhn checksum value for the given value.
+ *
+ * @param str The string to generate the checksum for.
+ */
+function luhnChecksum(str: string): number {
+  str = str.replace(/[\s-]/g, '');
+  let sum = 0;
+  let alternate = false;
+  for (let i = str.length - 1; i >= 0; i--) {
+    let n = parseInt(str.substring(i, i + 1));
+    if (alternate) {
+      n *= 2;
+      if (n > 9) {
+        n = (n % 10) + 1;
+      }
+    }
+    sum += n;
+    alternate = !alternate;
+  }
+  return sum % 10;
+}

test/finance.spec.ts

@@ -2,7 +2,7 @@ import { afterEach, describe, expect, it } from 'vitest';
 import { faker } from '../src';
 import { FakerError } from '../src/errors/faker-error';
 import ibanLib from '../src/modules/finance/iban';
-import { luhnCheck } from './support/luhnCheck';
+import { luhnCheck } from '../src/modules/helpers/luhn-check';
 
 const seedRuns = [
   {
@@ -19,7 +19,7 @@ const seedRuns = [
       currencySymbol: '₱',
       bitcoinAddress: '3XbJMAAara64sSkA9HD24YHQWd1b',
       litecoinAddress: '3XbJMAAara64sSkA9HD24YHQWd1b',
-      creditCardNumber: '3581-7755-1410-0486',
+      creditCardNumber: '3581-7755-1410-0484',
       creditCardCVV: '379',
       pin: '3791',
       ethereumAddress: '0x8be4abdd39321ad7d3fe01ffce404f4d6db0906b',
@@ -43,7 +43,7 @@ const seedRuns = [
       currencySymbol: '$',
       bitcoinAddress: '3adhxs2jewAgkYgJi7No6Cn8JZa',
       litecoinAddress: 'Madhxs2jewAgkYgJi7No6Cn8JZar',
-      creditCardNumber: '6011-6212-2540-3255-2392',
+      creditCardNumber: '6011-6212-2540-3255-2398',
       creditCardCVV: '251',
       pin: '2512',
       ethereumAddress: '0x5c346ba075bd57f5a62b82d72af39cbbb07a98cb',
@@ -67,7 +67,7 @@ const seedRuns = [
       currencySymbol: '₭',
       bitcoinAddress: '1TMe8Z3EaFdLqmaGKP1LEEJQVriSZRZdsA',
       litecoinAddress: 'MTMe8Z3EaFdLqmaGKP1LEEJQVriSZRZds',
-      creditCardNumber: '4872190616276',
+      creditCardNumber: '4872190616274',
       creditCardCVV: '948',
       pin: '9487',
       ethereumAddress: '0xeadb42f0e3f4a973fab0aeefce96dfcf49cd438d',

test/helpers.spec.ts

@@ -1,6 +1,6 @@
 import { afterEach, describe, expect, it } from 'vitest';
 import { faker } from '../src';
-import { luhnCheck } from './support/luhnCheck';
+import { luhnCheck } from '../src/modules/helpers/luhn-check';
 
 const seededRuns = [
   {
@@ -9,7 +9,7 @@ const seededRuns = [
       slugify: '',
       replaceSymbolWithNumber: '',
       replaceSymbols: '',
-      replaceCreditCardSymbols: '6453-3791-7755-1410-0481',
+      replaceCreditCardSymbols: '6453-3791-7755-1410-0489',
       repeatString: '',
       regexpStyleStringParse: '',
       shuffle: [],
@@ -23,7 +23,7 @@ const seededRuns = [
       slugify: '',
       replaceSymbolWithNumber: '',
       replaceSymbols: '',
-      replaceCreditCardSymbols: '6453-2512-2540-3255-2391',
+      replaceCreditCardSymbols: '6453-2512-2540-3255-2399',
       repeatString: '',
       regexpStyleStringParse: '',
       shuffle: [],
@@ -37,7 +37,7 @@ const seededRuns = [
       slugify: '',
       replaceSymbolWithNumber: '',
       replaceSymbols: '',
-      replaceCreditCardSymbols: '6453-9487-2190-6162-7436',
+      replaceCreditCardSymbols: '6453-9487-2190-6162-7434',
       repeatString: '',
       regexpStyleStringParse: '',
       shuffle: [],

test/phone.spec.ts

@@ -1,6 +1,6 @@
 import { beforeEach, describe, expect, it } from 'vitest';
 import { faker } from '../src';
-import { luhnCheck } from './support/luhnCheck';
+import { luhnCheck } from '../src/modules/helpers/luhn-check';
 
 const seededRuns = [
   {
@@ -35,7 +35,7 @@ const seededRuns = [
         noArgs: '(!##) !##-####',
       },
       imei: {
-        noArgs: '25-122540-325523-6',
+        noArgs: '25-122540-325523-4',
       },
     },
   },
@@ -53,7 +53,7 @@ const seededRuns = [
         noArgs: '1-!##-!##-#### x#####',
       },
       imei: {
-        noArgs: '94-872190-616274-6',
+        noArgs: '94-872190-616274-4',
       },
     },
   },