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(define-module (vcalendar recurrence generate)
#:use-module (srfi srfi-19) ; Datetime
#:use-module (srfi srfi-19 util)
#:use-module (srfi srfi-26) ; Cut
#:use-module (srfi srfi-41) ; Streams
#:use-module (ice-9 match)
#:use-module (util)
#:use-module (vcalendar)
#:use-module (vcalendar recurrence internal)
#:use-module (vcalendar recurrence parse)
#:export (generate-recurrence-set)
)
;;; TODO implement
;;; EXDATE and RDATE
;;; EXDATE (3.8.5.1)
;;; comma sepparated list of dates or datetimes.
;;; Can have TZID parameter
;;; Specifies list of dates that the event should not happen on, even
;;; if the RRULE say so.
;;; Can have VALUE field specifiying "DATE-TIME" or "DATE".
;;; RDATE (3.8.5.2)
;;; Comma sepparated list of dates the event should happen on.
;;; Can have TZID parameter.
;;; Can have VALUE parameter, specyfying "DATE-TIME", "DATE" or "PREIOD".
;;; PERIOD (see 3.3.9)
(define (seconds-in freq)
(case freq
((SECONDLY) 1)
((MINUTELY) 60)
((HOURLY) (* 60 60))
((DAILY) (* 60 60 24))
((WEEKLY) (* 60 60 24 7))))
;; Event x Rule → Event
(define (next-event ev r)
(let ((e (copy-vcomponent ev)))
(cond
((memv (freq r) '(SECONDLY MINUTELY HOURLY DAILY WEEKLY))
(mod! (attr e 'DTSTART)
;; Previously I had the mutating version of
;; @var{add-duration(!)} here. However since
;; @var{copy-vcomponent} doesn't do a deep copy that
;; modified the attribute for all items in the set,
;; breaking everything.
(cut add-duration <>
(make-duration
(* (interval r) ; INTERVAL
(seconds-in (freq r)))))))
((memv (freq r) '(MONTHLY YEARLY))
#f ; Hur fasen beräkrnar man det här!!!!
))
(set! (attr e 'DTEND)
(add-duration (attr e 'DTSTART) (attr e 'DURATION)))
;; Return
e))
;; BYDAY and the like depend on the freq?
;; Line 7100
;; Table @@ 2430
;;
;; Event x Rule → Bool (continue?)
;; Alternative, monadic solution using <optional>.
;; @example
;; (optional->bool
;; (do (<$> (cut time<=? (attr last 'DTSTART)) (until r))
;; (<$> (negate zero?) (count r))
;; (just #t)))
;; @end example
(define-stream (recur-event-stream event rule-obj)
(stream-unfold
;; Event x Rule → Event
car
;; Event x Rule → Bool (continue?)
(match-lambda
((e r)
(or (and (not (until r)) (not (count r))) ; Never ending
(and=> (count r) (negate zero?)) ; COUNT
(and=> (until r) (cut time<=? (attr e 'DTSTART) <>))))) ; UNTIL
;; Event x Rule → next (Event, Rule)
(match-lambda
((e r)
(list (next-event e r)
(if (count r)
;; Note that this doesn't modify, since r is immutable.
(mod! (count r) 1-)
r ))))
;; Seed
(list event rule-obj)))
(define (generate-recurrence-set event)
(unless (attr event "DURATION")
(set! (attr event "DURATION")
(time-difference
(attr event "DTEND")
(attr event "DTSTART"))))
(recur-event-stream event (parse-recurrence-rule (attr event "RRULE"))))
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