Re: [POLL] Dealing with +1m/y repeaters when jumping to impossible date (should 05-31 +1m be 07-01 or 06-30?)

[Ihor Radchenko <yantar92@posteo.net>]

Max Nikulin <manikulin@gmail.com> writes:

> On 13/05/2024 17:07, Ihor Radchenko wrote:
>> 
>> However, there are still some issues remaining.
>> When updating timestamps repeating monthly across months with 30, 31,
>> and 28 days we get
>> 
>> <2025-01-31 Fri +1m>
>> <2025-02-28 Fri +1m>
>> <2025-03-28 Fri +1m>
>> ...
>> <2026-01-28 Wed +1m>
>
> Instead of using timestamp obtained on previous step, use original 
> timestamp and multiple of the interval.

This is not possible because of how `org-auto-repeat-maybe' is designed.
When repeater is triggered, the original date in the timestamp is
replaced with future date. So, we have no access to the original date in
the timestamp.

> I have the following in my notes. However I have not find suitable 
> functions in elisp:
>
> https://debbugs.gnu.org/54764#10
> Paul Eggert. Sat, 9 Apr 2022 00:52:57 -0700
>> Generally speaking, 
>> when Org mode is doing calendrical calculations it should use 
>> calendrical functions rather than encode-time+decode-time, which are 
>> best used for time calculations not calendar calculations.
>
> Do you have any idea what Paul was writing about?

No idea. I am not aware about any existing built-in API that provides
date increments.

>> +          (org-encode-time
>> +           (list
>> +            (+ (if (eq unit 'second) value 0) (decoded-time-second time))
>> +            (+ (if (eq unit 'minute) value 0) (decoded-time-minute time))
>> +            (+ (if (eq unit 'hour) value 0)   (decoded-time-hour time))
>> +            (+ (if (eq unit 'day) value 0)    (decoded-time-day time))
>
> Have you considered using `min' with result of `date-days-in-month' here 
> (or its sibling from timezone.el)?

Not sure if it is going to be simpler.

>> +(defun org-time-inc (unit value time)
> Is there a chance that support of intervals like 1h20m will be required 
> later?

Not sure again. I simply used ts-inc function signature from Adam's
ts.el as reference.

>> +            (+ (if (eq unit 'month) value 0)  (decoded-time-month time))
>> +            (+ (if (eq unit 'year) value 0)   (decoded-time-year time))
>> +            (decoded-time-weekday time)
>> +            (if (memq unit '(day month year))
>> +                nil ; Avoid auto-adjustments of time when jumping across DST.
>
> Sorry, but you have to use -1, otherwise
>
> (format-time-string
>   "%F %T %Z %z"
>   (encode-time '(0 30 12 15 1 2000 'ignored nil "Africa/Juba"))
>   "Africa/Juba")
> (error "Specified time is not representable")

Hmm. I am not sure if it is a real problem in practice.
String values of time zone are only possible for hand-crafted time
values. Using `decode-time' does not retain the time zone name:

(decode-time
  (encode-time '(0 30 12 15 1 2000 'ignored -1 "Africa/Juba")))
; => (0 30 12 15 1 2000 6 nil 7200)

The reason why I forced DST nil is hysteresis of glibc when dealing with
DST transitions:

(cl-loop for m in '(1 2 3 4 5 6 7 8 9 10 11 12)
  collect (decode-time (encode-time `(0 0 0 4 ,m 2012 nil -1 10800))))

(0 0 23 3 1 2012 2 nil 7200)
(0 0 23 3 2 2012 5 nil 7200)
(0 0 23 3 3 2012 6 nil 7200)
(0 0 0  4 4 2012 3 t 10800)
(0 0 0  4 5 2012 5 t 10800)
(0 0 0  4 6 2012 1 t 10800)
(0 0 0  4 7 2012 3 t 10800)
(0 0 0  4 8 2012 6 t 10800)
(0 0 0  4 9 2012 2 t 10800)
(0 0 0  4 10 2012 4 t 10800)
(0 0 23 3 11 2012 6 nil 7200)
(0 0 23 3 12 2012 1 nil 7200)

Although, forcing DST nil will not always help here, so I need some
other solution to this problem.
(timezones, DSTs... :sigh:)

>> +              (decoded-time-dst time))
>> +            (decoded-time-zone time))))))
>> +    (if (not org-repeat-round-time) new-time
> I am in doubts if `org-time-inc' should access `org-repeat-round-time' 
> directly or its value should be passed as an explicit argument. Perhaps 
> the additional argument may be optional with fallback to 
> `org-repeat-round-time' when it is omitted.

This is of no use for now - we do not need to pass different parameters
to `org-time-inc' from the existing Org code. But we can always add an
extra optional argument if necessary.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>