siret-validator.ts

import { AbstractControl, ValidationErrors } from '@angular/forms';

const luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];

// https://portal.hardis-group.com/pages/viewpage.action?pageId=120357227
export function checkSIRET(control: AbstractControl): ValidationErrors {
  if (!control.value) {
    return null;
  }

  const siret = (control.value as string).replace(/\s/g, '') as string;

  if (!/^\d{14}$/.test(siret)) {
    return { invalidFormat: { siret } };
  }

  const numbers = siret.split('').map((v) => parseInt(v));
  const checksum = numbers.reduce((a, e, i) => a + ((i & 1) ? e : luhnArr[e]), 0);
  if (checksum % 10) {
    return { invalidChecksum: { siret } };
  }

  return null;
}