(function (global, factory) {
  'use strict';

  /* eslint-disable no-undef */
  if (typeof exports === 'object' && typeof module !== 'undefined') {
    module.exports = factory();
  } else if (typeof define === 'function' && define.amd) {
    define(factory);
  } else {
    global.saIdParser = factory();
  }
  /* eslint-enable */
}(this, function () {
  'use strict';

  /**
   * Parsing result for a valid South African ID number.
   *
   * @typedef {Object} ValidIDParseResult
   * @property {boolean} isValid - true
   * @property {Date} dateOfBirth - The date of birth from the ID number.
   * @property {boolean} isMale - The sex from the ID number - true if male, false if female.
   * @property {boolean} isFemale - The sex from the ID number - true if female, false if male.
   * @property {boolean} isSouthAfricanCitizen - Citizenship status from the ID
   *   number, true if it indicates South African citizenship.
   */

  /**
   * Parsing result for a invalid South African ID number.
   *
   * @typedef {Object} InvalidIDParseResult
   * @property {boolean} isValid - false
   */

  return {
    /**
     * Validates and ID number and parses out all information from it.
     *
     * This is a combination of the other parsing and validation functions, so
     * refer to their documentation for any details.
     *
     * @function
     * @param {string} idNumber - The ID number to be parsed.
     * @return {ValidIDParseResult|InvalidIDParseResult} An object with all of
     *   the parsing results. If the ID is invalid, the result is an object with
     *   just an `isValid` property set to false.
     *
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     *
     * var info = saIdParser.parse(validIdNumber);
     * // info === {
     * //   isValid: true,
     * //   dateOfBirth: new Date(1990, 0, 4),
     * //   isMale: true,
     * //   isFemale: false,
     * //   isSouthAfricanCitizen: true
     * // }
     *
     * var invalidIdNumber = '1234567';
     * info = saIdParser.parse(invalidIdNumber);
     * // info === {
     * //   isValid: false
     * // }
     */
    parse: function(idNumber) {
      var isValid = validate(idNumber);
      if (!isValid) {
        return {
          isValid: false
        };
      }

      return {
        isValid: isValid,
        dateOfBirth: parseDateOfBirth(idNumber),
        isMale: parseIsMale(idNumber),
        isFemale: parseIsFemale(idNumber),
        isSouthAfricanCitizen: parseIsSouthAfricanCitizen(idNumber)
      };
    },

    /**
     * Validates an ID number.
     *
     * This includes making sure that it follows the expected 13 digit pattern,
     * checking that the control digit is correct, and checking that the date of
     * birth is a valid date.
     *
     * @function
     * @param {string} idNumber - The ID number to be validated.
     * @return {boolean} True if the ID number is a valid South African ID number.
     *
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     * var isValid = saIdParser.validate(validIdNumber);
     *
     * // valid === true
     */
    validate: function(idNumber) {
      return validate(idNumber);
    },

    /**
     * Parses the date of birth out of an ID number.
     *
     * Minimal validation of the ID number is performed, requiring only that
     * it's 13 digits long.
     *
     * The date of birth included in the ID number has a two digit year. For
     * example, 90 instead of 1990. This is converted to a full date by
     * comparing the date of birth to the current date, and choosing the century
     * that gives the person the lowest age, while still putting their age in
     * the past.
     *
     * For example, assuming that the current date is 10 December 2015. If the
     * date of birth parsed is 10 December 15, it will be interpreted as 10
     * December 2015. If, on the other hand, the date of birth is parsed as 11
     * December 15, that will be interpreted as 10 December 1915.
     *
     * The date will be in the local timezone, with the time portion set to
     * midnight.
     *
     * @function
     * @param {string} idNumber - The ID number to be parsed.
     * @return {?Date} The date of birth from the ID number, or undefined if the
     *   ID number is not formatted correctly or does not have a valid date of
     *   birth.
     *
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     * var dateOfBirth = saIdParser.parseDateOfBirth(validIdNumber);
     *
     * // dateOfBirth === new Date(1990, 0, 4)
     */
    parseDateOfBirth: function(idNumber) {
      return parseDateOfBirth(idNumber);
    },

    /**
     * Parses the sex out of the ID number and returns true it is male.
     *
     * Minimal validation of the ID number is performed, requiring only that
     * it's 13 digits long.
     *
     * @function
     * @param {string} idNumber - The ID number to be parsed.
     * @return {?boolean} True if male, false if female. Returns undefined if the
     *   ID number is not a 13 digit number.
     *
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     * var isMale = saIdParser.parseIsMale(validIdNumber);
     *
     * // isMale === true
     */
    parseIsMale: function(idNumber) {
      return parseIsMale(idNumber);
    },

    /**
     * Parses the sex out of the ID number and returns true it is female.
     *
     * Minimal validation of the ID number is performed, requiring only that
     * it's 13 digits long.
     *
     * @function
     * @param {string} idNumber - The ID number to be parsed.
     * @return {?boolean} True if female, false if male. Returns undefined if the
     *   ID number is not a 13 digit number.
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     * var isFemale = saIdParser.parseIsFemale(validIdNumber);
     *
     * // isFemale === false
     */
    parseIsFemale: function(idNumber) {
      return parseIsFemale(idNumber);
    },

    /**
     * Parses the citizenship status out of an ID number and returns true if it
     * indicates South African citizen.
     *
     * Minimal validation of the ID number is performed, requiring only that
     * it's 13 digits long.
     *
     * @function
     * @param {string} idNumber - The ID number to be parsed.
     * @return {?boolean} True if the ID number belongs to a South African
     *   citizen. Returns undefined if the ID number is not a 13 digit number.
     *
     * @example
     * var saIdParser = require('south-african-id-parser');
     * var validIdNumber = '9001049818080';
     * var isSouthAfricanCitizen = saIdParser.parseIsSouthAfricanCitizen(validIdNumber);
     *
     * // isSouthAfricanCitizen === true
     */
    parseIsSouthAfricanCitizen: function(idNumber) {
      return parseIsSouthAfricanCitizen(idNumber);
    }
  };

  function validate(idNumber) {
    if (!regexpValidate(idNumber) || !datePartValidate(idNumber) || !controlDigitValidate(idNumber)) {
      return false;
    }

    return true;
  }

  function regexpValidate(idNumber) {
    if (typeof(idNumber) !== 'string') {
      return false;
    }
    var regexp = /^[0-9]{13}$/;
    return regexp.test(idNumber);
  }

  function datePartValidate(idNumber) {
    var dateOfBirth = parseDateOfBirth(idNumber);
    return !!dateOfBirth;
  }

  function controlDigitValidate(idNumber) {
    var checkDigit = parseInt(idNumber[12], 10);

    var oddDigitsSum = 0;

    for (var i = 0; i < idNumber.length - 1; i+=2) {
      oddDigitsSum += parseInt(idNumber[i], 10);
    }
    var evenDigits = '';
    for (var j = 1; j < idNumber.length - 1; j+=2) {
      evenDigits += idNumber[j];
    }
    evenDigits = parseInt(evenDigits, 10);
    evenDigits *= 2;
    evenDigits = '' + evenDigits;

    var sumOfEvenDigits = 0;
    for (var k = 0; k < evenDigits.length; k++) {
      sumOfEvenDigits += parseInt(evenDigits[k], 10);
    }
    var total = sumOfEvenDigits + oddDigitsSum;
    var computedCheckDigit = 10 - (total % 10);

    if (computedCheckDigit === 10) {
      computedCheckDigit = 0;
    }
    return computedCheckDigit === checkDigit;
  }

  function parseDateOfBirth(idNumber) {
    if (!regexpValidate(idNumber)) {
      return undefined;
    }

    // get year, and assume century
    var currentYear = new Date().getFullYear();
    var currentCentury = Math.floor(currentYear/100)*100;
    var yearPart = currentCentury + parseInt(idNumber.substring(0,2), 10);
    if (yearPart > currentYear) {
      yearPart -= 100; //must be last century
    }

    // In Javascript, Jan=0. In ID Numbers, Jan=1.
    var monthPart = parseInt(idNumber.substring(2,4), 10)-1;

    var dayPart = parseInt(idNumber.substring(4,6), 10);

    var dateOfBirth = new Date(yearPart, monthPart, dayPart);

    // validate that date is in a valid range by making sure that it wasn't 'corrected' during construction
    if (!dateOfBirth || dateOfBirth.getFullYear() !== yearPart || dateOfBirth.getMonth() !== monthPart || dateOfBirth.getDate() !== dayPart) {
      return undefined;
    }

    return dateOfBirth;
  }

  function parseIsMale(idNumber) {
    return !parseIsFemale(idNumber);
  }

  function parseIsFemale(idNumber) {
    if (!regexpValidate(idNumber)) {
      return undefined;
    }
    return parseInt(idNumber[6], 10) <= 4;
  }

  function parseIsSouthAfricanCitizen(idNumber) {
    if (!regexpValidate(idNumber)) {
      return undefined;
    }
    return parseInt(idNumber[10], 10) === 0;
  }
}));