Validator for Library of Congress's Extended Date/Time Format (Level 1)

edtf-lvl1-validator.js

var isValidEDTF = function (str) {
  var verdict,
    intervals = str.split('/'),
    validateSingleDate;

  validateSingleDate = function(dateString) {
    var verdict,
      sepMarks = dateString.split(/([?~]*)$/),
      dateParts = sepMarks[0].split('-'),
      possiblyUnclearYear = /^-?[0-9]{0,2}(?:[0-9]{2}|[0-9]u|uu)$/,
      knownYear = /^-?(?:[0-9]{1,4}|y[0-9]{5,})/,
      possiblyUnclear = /^(?:[0-9]{2}|uu)$/,
      year,
      month,
      day;


    if (dateParts.length == 1) {
      // Valid if this is only a year (possibly unclear).

      year = dateParts[0];

      verdict = possiblyUnclearYear.test(year) || knownYear.test(year)

    } else if (dateParts.length == 2) {
      // Valid if this is a year (definitely known) and a month (possibly unclear)

      year = dateParts[0];
      month = dateParts[1];

      verdict = knownYear.test(year) && possiblyUnclear.test(month);
      if (/[0-9]/.test(month)) {
        verdict = ( month >= 1 && month <= 12 ||
                    month >= 21 && month <= 24 ) && verdict
      }

    } else if (dateParts.length == 3) {
      // Valid is this is a year (definitely known) and one of the following:
      // 1. Known month & possibly unclear day
      // 2. Unclear month & unclear day

      year = dateParts[0];
      month = dateParts[1];
      day = dateParts[2].split('T')[0]

      verdict = knownYear.test(year) &&
                  ( /^[0-9]{2}$/.test(month) && possiblyUnclear.test(day) ) ||
                  ( /^uu$/.test(month) && /^uu$/.test(day) )
      if (/[0-9]/.test(month)) {
        verdict = ( month >= 1 && month <= 12 ) && verdict
      }
      if (/[0-9]/.test(day)) {
        verdict = ( day >= 1 && day <= 31 ) && verdict
      }
    } else {
      verdict = false;
    }
    return verdict;
  }
  
  /*
   * Test one or two dates, depending on if date is an interval.
   */

  if (intervals.length == 1) {
    verdict = validateSingleDate(intervals[0]);
  } else if (intervals.length == 2) {
    // The first part of an interval can be 'unknown'; second 'open' or 'unknown'
    verdict = ( validateSingleDate(intervals[0]) || /^unknown$/.test(intervals[0]) ) &&
              ( validateSingleDate(intervals[1]) || /^(?:open|unknown)$/.test(intervals[1]) );
  } else {
    verdict = false;
  }
  
  return verdict;
}