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fix(mx/rfc): do not enforce check digit, matching python-stdnum default behavior #163

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fix(mx/rfc): do not enforce check digit, matching python-stdnum default behavior #163

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22 changes: 17 additions & 5 deletions src/mx/rfc.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -37,11 +37,13 @@ describe('mx/rfc', () => {
expect(result.isValid && result.compact).toEqual('SALC7304253S0');
});

// it('validate:XEXX010101000', () => {
// const result = validate('XEXX010101000');
it('validate:XEXX010101000', () => {
// Generic RFC for foreign residents; its serial/check digits do not
// follow the check digit algorithm but it is a real, valid RFC
const result = validate('XEXX010101000');

// expect(result.isValid && result.compact).toEqual('XEXX010101000');
// });
expect(result.isValid && result.compact).toEqual('XEXX010101000');
});

it('validate:RET130705MD5', () => {
const result = validate('RET130705MD5');
Expand All @@ -56,9 +58,19 @@ describe('mx/rfc', () => {
});

it('validate:VACE-460910-SX6', () => {
// python-stdnum docstring example: fails the check digit algorithm but
// is accepted because check digit validation is disabled by default
const result = validate('VACE-460910-SX6');

expect(result.isValid).toEqual(false);
expect(result.isValid && result.compact).toEqual('VACE460910SX6');
});

it('validate:PAF-070213-GI1', () => {
// SAT-issued company RFC whose check digit does not match the published
// algorithm (expected 'A'); must validate like python-stdnum does
const result = validate('PAF-070213-GI1');

expect(result.isValid && result.compact).toEqual('PAF070213GI1');
});

it('validate:SOTO800101110', () => {
Expand Down
47 changes: 2 additions & 45 deletions src/mx/rfc.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@
*/

import * as exceptions from '../exceptions';
import { isValidDateCompactYYMMDD, strings, weightedSum } from '../util';
import { isValidDateCompactYYMMDD, strings } from '../util';
import { Validator, ValidateReturn } from '../types';

function clean(input: string): ReturnType<typeof strings.cleanUnicode> {
Expand Down Expand Up @@ -80,13 +80,6 @@ const nameBlacklist = new Set([
'RUIN',
]);

// Official alphabet per SAT (Anexo 20). Includes '&' and 'Ñ'.
const checkAlphabet = '0123456789ABCDEFGHIJKLMN&OPQRSTUVWXYZ Ñ';

// Legacy alphabet (Base 36) used in older systems.
// It excludes '&' and 'Ñ'. Space is added to support padding for companies.
const checkAlphabetLegacy = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ ';

const impl: Validator = {
name: 'Mexican Tax Number',
localName: 'Registro Federal de Contribuyentes',
Expand Down Expand Up @@ -145,42 +138,6 @@ const impl: Validator = {
return { isValid: false, error: new exceptions.InvalidLength() };
}

if (value.length >= 12) {
if (!/[1-9A-V][1-9A-Z][0-9A]$/.test(value)) {
return { isValid: false, error: new exceptions.InvalidComponent() };
}

const [front, check] = strings.splitAt(value, -1);
const paddedInput = front.padStart(12, ' ');

const calculateChecksum = (alphabet: string) => {
const sum = weightedSum(paddedInput, {
modulus: 11,
alphabet: alphabet,
weights: [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14],
reverse: true,
});

const mod = 11 - (sum % 11);
if (mod === 11) return '0';
if (mod === 10) return 'A';
return String(mod);
};

// Try with official SAT alphabet first
const valOfficial = calculateChecksum(checkAlphabet);

if (check !== valOfficial) {
// If it fails, try with Legacy alphabet (Base 36)
// This handles older RFCs generated without '&' or 'Ñ' support
const valLegacy = calculateChecksum(checkAlphabetLegacy);

if (check !== valLegacy) {
return { isValid: false, error: new exceptions.InvalidChecksum() };
}
}
}

return {
isValid: true,
compact: value,
Expand All @@ -191,4 +148,4 @@ const impl: Validator = {
};

export const { name, localName, abbreviation, validate, format, compact } =
impl;
impl;