'use strict';

/**
 * Social Security number (SSN) is a 4-digit number following the date of birth 
 * in the format: YYYYMMDD-XXXX issued to Swedish citizens, permanent residents 
 * and/or individuals with educational registration.
 * 
 * The format length can either be 12 (full year) or 10 (short year) digits long.
 * E.g. 19900211-1234 (12) or instead 900211-1234 (10).
 *
 * See following link for more information.
 * https://www.skatteverket.se/servicelankar/otherlanguages/inenglish/individualsandemployees/movingtosweden/citizenofeueeacountry/youarestudying/youaremovingbyyourself.4.3810a01c150939e893f4157.html
 */

/**
 * Regular expression to match dates after 1800 and include possibility to be
 * over 100 years old. 
 */
const expression = /^(19|20)?(\d{6}\d{4}|(?!19|20)\d{10})$/;

/**
 * Validate function.
 */
function ssnIsValid(value) {
  return expression.test(value.replace(/\W/g, ''));
}

/**
 * Mask the SSN with "X" placeholders to protect sensitive data.
 * E.g. "12345678-1234" -> "XXXXXX78XX3X ", "123456-1234" -> "XXXX56XX3X".
 * The numbers left unmasked can be used to determine the gender and day of birth.
 */
function ssnMask(value) {
  value = value.replace(/\W/g, '');
  if (!ssnIsValid(value)) {
    throw new Error('Invalid Swedish Social Security Number');
  }

  switch (value.length) {
    case 12:
      // YYYY-MM-DD:NNNN
      return value.substr(0, 6).replace(/[\w]/g, 'X') + value.substr(6, 2) + value.substr(10, 10).replace(/[\w]/g, 'X') + value.substr(10, 1) + 'X';
    case 10:
      // YY-MM-DD:NNNN
      return value.substr(0, 4).replace(/[\w]/g, 'X') + value.substr(4, 2) + value.substr(8, 8).replace(/[\w]/g, 'X') + value.substr(8, 1) + 'X';
    default:
      throw new Error('Invalid Swedish Social Security Number');
  }
}

/**
 * Exports.
 */
module.exports = { ssnMask, ssnIsValid };