Vpim talk - May 2006 - [vpim] Support for RDATE

Quoting cosmin at speakeasy.net, on Sat, May 06, 2006 at 11:27:07AM
-0700:
>    I noticed a comment in the code and was wondering if I can bump the
>    priority on the ToDo list for this.
> 
>    I need support for RDATE when parsing recurrent events.
> 
>    Is there any chance on getting this in soon? Also, if you don''t
have
>    the time maybe you can point me what/where I need to change to
>    implement it. I''m just a newbie with Ruby, but I know a bit
more about
>    iCal/iTIP as I implemented a few years ago a C++ parser for this.
Thats great. Did you implement support for timezones? Ruby has only the support
that basic posix/C apis have, which is not good.


I think RDATE support means a few things, some easy, some taking more
work.


An RDATE field itself looks like it is allowed to occur just once.
Anyhow, its value is a list of date-time, date, or period values.
decode_date_time() and others in rfc2425.rb can decode these values. Its
a fixed length list, nowhere near as complex as RRULE. I can add support
for that with a fix I''m currently trying to get out to properly return
a Date for fields whose value is DATE.

Maybe thats all you need?

The bigger problem is to take multiple RRULE enumerators, the RDATE
array of values multiple EXRULE enumerators, an EXDATE array of values,
and integrate them into a single enumerator returning all the recurrence
times... thats a lot more work.

I don''t know if I''ll have the time for the full aggregation
support,
though I''ll bump it to next on the list after bug fixes.

The aggregation algorithm below could be implemented outside of vPim
initially.  If you implemented the algorithm, I''d be even happier to
take it and merge it into icalendar components! If you have implemented
the algorithm before, you might have a head start in doing it in ruby.

One thing that could help me is if you could send example calendar
components or calendars with the kinds of recurring events you need
support for, that would help a bunch.

Cheers,
Sam


RDATE ....

   Description: This property can appear along with the "RRULE"
property
   to define an aggregate set of repeating occurrences. When they both
   appear in an iCalendar object, the recurring events are defined by
   the union of occurrences defined by both the "RDATE" and
"RRULE".
    
   The recurrence dates, if specified, are used in computing the
   recurrence set. The recurrence set is the complete set of recurrence
   instances for a calendar component. The recurrence set is generated
   by considering the initial "DTSTART" property along with the
"RRULE",
   "RDATE", "EXDATE" and "EXRULE" properties
contained within the
   iCalendar object. The "DTSTART" property defines the first instance
   in the recurrence set. Multiple instances of the "RRULE" and
"EXRULE"
   properties can also be specified to define more sophisticated
   recurrence sets. The final recurrence set is generated by gathering
   all of the start date/times generated by any of the specified
"RRULE"
   and "RDATE" properties, and excluding any start date/times which
fall
   within the union of start date/times generated by any specified
   "EXRULE" and "EXDATE" properties. This implies that start
date/times
   within exclusion related properties (i.e., "EXDATE" and
"EXRULE")
   take precedence over those specified by inclusion properties (i.e.,
   "RDATE" and "RRULE"). Where duplicate instances are
generated by the
   "RRULE" and "RDATE" properties, only one recurrence is
considered.
   Duplicate instances are ignored.

Hi Sam,
>>  Thats great. Did you implement support for timezones? Ruby has only
the
>>   support
>>  that basic posix/C apis have, which is not good.
Yes, I did this in Windows though.
>>  I think RDATE support means a few things, some easy, some taking more
>>  work.
I need it for parsing some VCALENDARS that have VEVENTS with one RDATE property 
with a bunch of DATE values or VEVENTS with RRULE. I don''t have VEVENTS
with
both properties which I assume it''s a bit more work.
>>  An RDATE field itself looks like it is allowed to occur just once.
>>  Anyhow, its value is a list of date-time, date, or period values.
>>  decode_date_time() and others in rfc2425.rb can decode these values.
Its
>>  a fixed length list, nowhere near as complex as RRULE. I can add
support
>>  for that with a fix I''m currently trying to get out to
properly return
>>  a Date for fields whose value is DATE.
>>  Maybe thats all you need?
Currently, I''m using the occurs_in? method trying to extract recurrent 
occurances from a specific date range. I only get occurrences for events with 
RRULE. So adding the RDATE support will fix my issue.

>>  The bigger problem is to take multiple RRULE enumerators, the RDATE
>>  array of values multiple EXRULE enumerators, an EXDATE array of
values,
>>  and integrate them into a single enumerator returning all the
recurrence
>>  times... thats a lot more work.
Yes, I agree. No need for now. I didn''t get to implement those as well
in the
past as I didn''t have to deal with lots of interop issues (I only did
RRULE).
>>  I don''t know if I''ll have the time for the full
aggregation support,
>>  though I''ll bump it to next on the list after bug fixes.
>>  The aggregation algorithm below could be implemented outside of vPim
>>  initially.  If you implemented the algorithm, I''d be even
happier to
>>  take it and merge it into icalendar components! If you have
implemented
>>  the algorithm before, you might have a head start in doing it in ruby.
Ok. I could give it a try once I''m finishing my stuff.
>>  One thing that could help me is if you could send example calendar
>>  components or calendars with the kinds of recurring events you need
>>  support for, that would help a bunch.
Here are some of the events I need to parse:

   BEGIN:VEVENT
   DTSTART;VALUE=DATE:20000423
   DTEND;VALUE=DATE:20000424
   RDATE;VALUE=DATE:20000423,20010415,20020331
   SEQUENCE:0
   UID:SOME-GUID
   DTSTAMP:20060506T120000Z
   SUMMARY:Some event
   END:VEVENT

And another one:

   BEGIN:VEVENT
   DTSTART;VALUE=DATE:20021130
   DTEND;VALUE=DATE:20021201
   RDATE;VALUE=DATE:20021130
   SEQUENCE:0
   UID:ANOTHER-GUID
   DTSTAMP:20060420T120000Z
   SUMMARY:Another event
   END:VEVENT


Thank you in advance,
Cosmin