validateRut.ts

function filterChars(dv: string): string {
  let result = '';
  for (const c of dv) {
    if ((c >= '0' && c <= '9') || c === 'k') {
      result += c;
    }
  }
  return result;
}

function normalizeRUT(chars: string): string {
  return filterChars(chars.toLocaleLowerCase());
}

function lastChar(str: string): string {
  return str[str.length - 1];
}

function removeLastChar(str: string): string {
  return str.slice(0, -1);
}

function getWeight(j: number) {
  return parseInt('234567'[(j - 1) % 6]);
}

function sumAB(a: number, b: number): number {
  return a + b;
}

function weightedSum(rutWithoutDv: string) {
  const n = rutWithoutDv.length;
  return stringToArray(rutWithoutDv)
    .map((digit, i) => getWeight(n - i) * parseInt(digit))
    .reduce(sumAB);
}

function stringToArray(rutWithoutDv: string) {
  return rutWithoutDv.split('');
}

function extractRutWithoutDV(fullRut: string) {
  return removeLastChar(fullRut);
}

function extractDv(fullRut: string) {
  return lastChar(fullRut);
}

function hasValidParams(rut: string, dv: string) {
  return hasLessThanTwoChars(dv) && hasTwoOrMoreChars(dv + rut);
}

function hasTwoOrMoreChars(fullRut: string) {
  const r = normalizeRUT(fullRut);
  return r.length >= 2;
}

function hasLessThanTwoChars(dv: string) {
  const d = normalizeRUT(dv);
  return d.length <= 1;
}

function formatDv(d: number): string {
  return d === 10 ? 'k' : d.toString();
}

function validateRut(rut: string, dv = ''): boolean {
  if (!hasValidParams(rut, dv)) return false;
  const cleanRut = normalizeRUT(rut + dv);
  const r = extractRutWithoutDV(cleanRut);
  const d = extractDv(cleanRut);
  return generateDv(r) === d;
}

function generateDv(rutWithoutDv: string): string {
  const sum = weightedSum(rutWithoutDv);
  const d = (11 - (sum % 11)) % 11;
  return formatDv(d);
}

export { validateRut, generateDv };