pesel.ts

// See https://pl.wikipedia.org/wiki/PESEL#Data_urodzenia
// See https://en.wikipedia.org/wiki/PESEL#Birthdates
const CENTURY_MAP: {[k: number]: number} = {
  0: 1900,
  1: 2000,
  2: 2100,
  3: 2200,
  4: 1800,
};

export function isValid(pesel: string): boolean {
  if (pesel.length !== 11) {
    return false;
  }

  const digits: number[] = pesel.split('').map(Number);
  const checkWeights = [9, 7, 3, 1, 9, 7, 3, 1, 9, 7];

  const checkSum = checkWeights.reduce((sum, weight, idx) => {
    return sum + weight * digits[idx];
  }, 0);

  return checkSum % 10 === digits.pop();
}

export function getGender(pesel: string): 'f' | 'm' {
  const genderComponent = Number(pesel[9]);
  return genderComponent % 2 === 0 ? 'f' : 'm';
}

export function getBirthDate(pesel: string): Date {
  const yearComponent: number = Number(pesel.slice(0, 2));
  const monthComponent: number = Number(pesel.slice(2, 4));
  const day: number = Number(pesel.slice(4, 6));

  const century: number = CENTURY_MAP[Math.floor(monthComponent / 20)];
  const year = century + yearComponent;
  const month = monthComponent % 20;

  return new Date(`${year}-${month}-${day}`);
}