pass along timezone for timedates (mandatory!)

[RiedleroD]

ALL timedates should have their timezone attached! This is non-negotiable if we want this to work at all outside CET/CEST. I'm not even sure if we're not assuming GMT instead in some places. tbqh the time-related code is a mess and needs to be rewritten. We can't rely on only passing implicitly UTC-based timedates, especially in countries that have summertime/wintertime splits.

I suggest:

• for dates: YYYY-MM-DD+-HH:MM (e.g. 2024-10-22+02:00, in PHP Y-m-dP)
• for datetimes: YYYY-MM-DDTHH:MM+-HH:MM (e.g. 2024-10-22T05:40+02:00, in PHP Y-m-d\TH:iP)
• where +-HH:MM is the offset relative to UTC (e.g. CEST would be +02:00)
• yes there are timezones with offsets of non-whole hours
• tz prefix is either + or - depending on whether the timezone is ahead or behind UTC
• we don't care about seconds in any case

todos:

• [ ] Custom DateTime in/out helper class to enforce this rule
• [ ] Look into ways of making absolutely sure that no timezone-less dates ever get passed around
• [ ] Make sure we only save dates in the DB in local time (since summertime/wintertime can mess things up otherwise - 16:00 shouldn't suddenly be 17:00 when the time gets changed)
• [ ] Coordinate transition of format with frontend team (@mcquenji) formats can be adjusted if flutter's native functions don't like this way of formatting things - see also https://www.php.net/manual/en/datetimeimmutable.createfromformat.php and https://www.php.net/manual/en/datetime.format.php for avaliable options in php.

[mcquenji]

or we only store UTC timestamps which can be converted client side to the correct timezone

[RiedleroD]

I literally already explained why we can't do that

[mcquenji]

i dont get it

[RiedleroD]

I'll explain it in tomorrow's meeting. tldr time is fucked and we're the condom