utcTimeToDate static method

DateTime? utcTimeToDate({ required List<int> contentData, })

Converts a UTCTime value to a date.

Note: GeneralizedTime has 4 digits for the year and is used for X.509 dates past 2049. Parsing that structure hasn't been implemented yet.

contentData the UTCTime value to convert.

Implementation

static DateTime? utcTimeToDate({required List<int> contentData}) {
  /* The following formats can be used:
    YYMMDDhhmmZ
    YYMMDDhhmm+hh'mm'
    YYMMDDhhmm-hh'mm'
    YYMMDDhhmmssZ
    YYMMDDhhmmss+hh'mm'
    YYMMDDhhmmss-hh'mm'
    Where:
    YY is the least significant two digits of the year
    MM is the month (01 to 12)
    DD is the day (01 to 31)
    hh is the hour (00 to 23)
    mm are the minutes (00 to 59)
    ss are the seconds (00 to 59)
    Z indicates that local time is GMT, + indicates that local time is
    later than GMT, and - indicates that local time is earlier than GMT
    hh' is the absolute value of the offset from GMT in hours
    mm' is the absolute value of the offset from GMT in minutes */

  String? utc;
  try {
    utc = utf8.decode(contentData);
  } catch (e) {}
  if (utc == null) {
    return null;
  }

  // if YY >= 50 use 19xx, if YY < 50 use 20xx
  var year = int.parse(utc.substring(0, 2), radix: 10);
  year = (year >= 50) ? 1900 + year : 2000 + year;
  // ignore: non_constant_identifier_names
  var MM = int.parse(utc.substring(2, 4), radix: 10);
  // ignore: non_constant_identifier_names
  var DD = int.parse(utc.substring(4, 6), radix: 10);
  var hh = int.parse(utc.substring(6, 8), radix: 10);
  var mm = int.parse(utc.substring(8, 10), radix: 10);
  var ss = 0;

  int? end;
  String? c;
  // not just YYMMDDhhmmZ
  if (utc.length > 11) {
    // get character after minutes
    c = utc[10];
    end = 10;

    // see if seconds are present
    if (c != '+' && c != '-') {
      // get seconds
      ss = int.parse(utc.substring(10, 12), radix: 10);
      end += 2;
    }
  }

  var date = DateTime.utc(year, MM, DD, hh, mm, ss, 0);

  if (end != null) {
    // get +/- after end of time
    c = utc[end];
    if (c == '+' || c == '-') {
      // get hours+minutes offset
      var hhoffset =
          int.parse(utc.substring(end + 1, end + 1 + 2), radix: 10);
      var mmoffset =
          int.parse(utc.substring(end + 4, end + 4 + 2), radix: 10);

      // calculate offset in milliseconds
      var offset = hhoffset * 60 + mmoffset;
      offset *= 60000;

      var offsetDuration = Duration(milliseconds: offset);
      // apply offset
      if (c == '+') {
        date.subtract(offsetDuration);
      } else {
        date.add(offsetDuration);
      }
    }
  }

  return date;
}