Sub-day recurrences

[Mike Samuel]

A couple people have expressed interest in implementing sub-day
recurrences.

http://code.google.com/p/google-rfc-2445/source/browse/trunk/src/com/google/ical/iter/RecurrenceIteratorFactory.java
is the class that would have to decode the byhour rules etc., and
http://code.google.com/p/google-rfc-2445/source/browse/trunk/src/com/google/ical/iter/RRuleIteratorImpl.java
around line 253 is where the byhour/byminute/bysecond rules could be
applied.

They need to be applied before the BYSETPOS rules are evaluated in
http://code.google.com/p/google-rfc-2445/source/browse/trunk/src/com/google/ical/iter/InstanceGenerators.java

It might help to define generators (see Generators.java) for each of
Hour/Minute/Second and extend the nested loop in
InstanceGenerators.java to invoke those generators. You would
probably have to define a generator that generates given a set, a
ByHourGenerator, and a default one that generates a single time per
day from the dtstart.

Perhaps these 3 kinds of tests would be useful
(1) Testing sub-day rules
RRULE:FREQ=HOURLY
(2) Testing longer period rules with BYHOUR
RRULE:FREQ=YEARLY;BYHOUR=4,12,20
(3) Testing interaction between BYSETPOS and other rules
RRULE:FREQ=HOURLY;BYSETPOS=3.-3
RFC 2445 has a section with a bunch of testcases.
http://code.google.com/p/google-rfc-2445/source/browse/trunk/test/com/google/ical/iter/RRuleIteratorImplTest.java
contains most of those except for the sub-day ones.

[jvdneste]

If anyone is already spending time on this, give a shout. I will
mostly likely have a look at it soon.

Mike: Thanks for the above pointers. Is there a high-level document
explaining how the library is implemented?

[jvdneste]

> Mike: Thanks for the above pointers. Is there a high-level document
> explaining how the library is implemented?

Nevermind, I think I understand most of it.Still figuring out some
parts...

[jvdneste]

I seems to me that a *lot* of places where DateValue is used now need
DateTimeValue. I implemented some generators, and started some
refactoring on an as-needed basis, but it's turning out to be more
work than I thought it would be. (keeping unittests up to date etc.)

Anyway, I'm still on it.

[Denis Hennessy]

The other thing to bear in mind with sub-day recurrences is that
dealing with timezones and DST effects are really important. So, for
example, with a 30 minute recurrence there will be times where it
jumps ahead by an hour and times when it goes backwards....

Of course, it actually spits out an event every 30 minutes as you'd
expect. The important thing is to make sure that the reported times
are in the requested timezone, which is specified to the createXXX()
call, even across DST changes.

/dh

[Neal Gafter]

I think recurrence rules are supposed to compute raw times independent
of time zone. The time zone should be applied later to the results.

[Mike Samuel]

I put together http://code.google.com/p/google-rfc-2445/wiki/LifeOfARecurrence
which is a high level design. Let me know if that answers/doesn't
answer your questions.

[Mike Samuel]

I'm confused. The generators all deal with a DTBuilder which should
have all the fields you need, so the InstanceGenerators should be the
only bit that needs to generate a DateValue or DateTimeValue from the
DTBuilder.

[Johan Van den Neste]

but the date iterators now no longer return date values, but date time values

--
Johan Van den Neste

[Mike Samuel]

2008/5/7 Johan Van den Neste <jvdn...@gmail.com>:

but the date iterators now no longer return date values, but date time values

date time values are date values though.

From http://code.google.com/p/google-rfc-2445/source/browse/trunk/src/com/google/ical/values/DateTimeValue.java

public interface DateTimeValue extends DateValue, TimeValue

 

[Johan Van den Neste]

> date time values are date values though.

true, but you actually want to receive them as date time values

[Mike Samuel]

2008/5/7 Johan Van den Neste <jvdn...@gmail.com>:

> date time values are date values though.

true, but you actually want to receive them as date time values

I don't want to receive a date time value when the DTSTART has no time.
If you iterate RRULE:FREQ=DAILY with DTSTART:20080508 then you get back date values, but if you iterate the same recurrence with DTSTART:20080508T120000 then you get back date time values.