heyho!

i devel'd a system that needed all those features once. here are some things that might help:

$weeknum = $yday / 52 ($yday as returned from localtime() )
i always stored the seconds since epoch in the DB, cause manipulating integers is way much funner than dealing with dates (only humans could have thought of such an incredibly computing-unfriendly concept).

watch out for DST-hour shifts! i can't really recall where that was, but i checked for e.g. "messages received in a particular week" using offsets (coded in S.S.E.s), and that is if a week/month/day has an extra hour somewhere, that really messes things up. try to convert the offset to SSE using functions of the TIME package on cpan.

when using SQL, try to avoid storing the SSEs in the DB - rather use a time-to-sql-timeformat-conversion function...that was you'll avoid a couple of problems later on.

hope i could help, and i'm always willing to help,

M.