Check if string is of SortableDateTimePattern format - regex

Question

Is there any way I can easily check if a string conforms to the SortableDateTimePattern ("s"), or do I need to write a regular expression?
I've got a form where users can input a copyright date (as a string), and these are the allowed formats:
Year: YYYY (eg 1997)
Year and month: YYYY-MM (eg 1997-07)
Complete date: YYYY-MM-DD (eg 1997-07-16)
Complete date plus hours and minutes: YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00)
Complete date plus hours, minutes and seconds: YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00)
Complete date plus hours, minutes, seconds and a decimal fraction of a second
YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)
I don't have much experience of writing regular expressions so if there's an easier way of doing it I'd be very grateful!

Answer 1

Not thoroughly tested and hence not foolproof, but the following seems to work:
var regex:RegExp = /(?<=\s|^)\d{4}(-\d{2}(-\d{2}(T\d{2}:\d{2}(:\d{2}(\.\d{2})?)?\+\d{2}:\d{2})?)?)?(?=\s|$)/g;
var test:String = "23 1997 1998-07 1995-07s 1937-04-16 " +
"1970-0716 1993-07-16T19:20+01:01 1979-07-16T19:20+0100 " +
"2997-07-16T19:20:30+01:08 3997-07-16T19:20:30.45+01:00";
var result:Object
while(result = regex.exec(test))
trace(result[0]);
Traced output:
1997
1998-07
1937-04-16
1993-07-16T19:20+01:01
2997-07-16T19:20:30+01:08
3997-07-16T19:20:30.45+01:00
I am using ActionScript here, but the regex should work in most flavors. When implementing it in your language, note that the first and last / are delimiters and the last g stands for global.

Answer 2

I'd split the input field into many (one for year, month, day etc.).
You can use Javscript to advance from one field to the next once full (i.e. once four characters are in the year box, move focus to month) for smoother entry.
You can then validate each field independently and finally construct the complete date string.