xmpp-vala: Improve time parsing

xmpp-vala/src/module/xep/0082_date_time_profiles.vala

@@ -1,32 +1,14 @@
 namespace Xmpp.Xep.DateTimeProfiles {
 
 public DateTime? parse_string(string time_string) {
-    Regex DATETIME_REGEX = new Regex("""^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})(\.(\d{3}))?(Z|((\+|\-)(\d{2})(:(\d{2}))?))$""");
-    MatchInfo match_info;
-    if (DATETIME_REGEX.match(time_string, RegexMatchFlags.ANCHORED, out match_info)) {
-        int year = int.parse(match_info.fetch(1));
-        int month = int.parse(match_info.fetch(2));
-        int day = int.parse(match_info.fetch(3));
-        int hour = int.parse(match_info.fetch(4));
-        int minute = int.parse(match_info.fetch(5));
-        int second = int.parse(match_info.fetch(6));
-        DateTime datetime = new DateTime.utc(year, month, day, hour, minute, second);
-        if (match_info.fetch(9) != "Z") {
-            char plusminus = match_info.fetch(11)[0];
-            int tz_hour = int.parse(match_info.fetch(12));
-            int tz_minute = int.parse(match_info.fetch(13));
-            if (plusminus == '-') {
-                tz_hour *= -1;
-                tz_minute *= -1;
-            }
-            datetime.add_hours(tz_hour);
-            datetime.add_minutes(tz_minute);
-        }
-        return datetime;
+    TimeVal time_val = new TimeVal();
+    if (time_val.from_iso8601(time_string)) {
+        return new DateTime.from_unix_utc(time_val.tv_sec);
     }
     return null;
 }
 
+
 public string to_datetime(DateTime time) {
     return time.to_utc().format("%Y-%m-%dT%H:%M:%SZ");
 }