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(define-module (vcomponent timezone)
:use-module (vcomponent base)
:use-module ((srfi srfi-1) :select (find))
:use-module (srfi srfi-19)
:use-module (srfi srfi-19 util)
:use-module (srfi srfi-41)
:use-module (srfi srfi-41 util)
:use-module (util)
:use-module ((vcomponent recurrence generate) :select (generate-recurrence-set))
:use-module ((vcomponent datetime) :select (ev-time<?))
)
;;@begin example
;; <VTIMEZONE> :: "#<vcomponent 558c5da80fc0>"
;; TZID: Europe/Stockholm
;; X-LIC-LOCATION: Europe/Stockholm
;; : <DAYLIGHT> :: "#<vcomponent 558c5e11e7c0>"
;; : RRULE: FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
;; : DTSTART: 19700329T020000
;; : TZNAME: CEST
;; : TZOFFSETTO: +0200
;; : TZOFFSETFROM: +0100
;; : <STANDARD> :: "#<vcomponent 558c5e11e7e0>"
;; : RRULE: FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
;; : DTSTART: 19701025T030000
;; : TZNAME: CET
;; : TZOFFSETTO: +0100
;; : TZOFFSETFROM: +0200
;; @end example
;;; GENERAL INFINITE EXTRAPOLATION OF TIMEZONE DATA IS IMPOSSIBLE, SINCE TIMEZONES
;;; DON'T CHANGE THAT PREDICTABLY
;; @begin example
;; BEGIN:VTIMEZONE
;; TZID:Europe/Stockholm
;; BEGIN:STANDARD
;; DTSTART;VALUE=DATE-TIME:20181028T020000
;; TZNAME:CET
;; TZOFFSETFROM:+0200
;; TZOFFSETTO:+0100
;; END:STANDARD
;; BEGIN:DAYLIGHT
;; DTSTART;VALUE=DATE-TIME:20190331T030000
;; TZNAME:CEST
;; TZOFFSETFROM:+0100
;; TZOFFSETTO:+0200
;; END:DAYLIGHT
;; END:VTIMEZONE
;; @end example
;; This should really be parsed as:
;; STANDARD : [2018-10-28 02:00, 2019-03-31 03:00)
;; DAYLIGHT : [2019-03-21 03:00, ∞)
;; Given a tz stream of length 2, takes the time difference between the DTSTART
;; of those two. And creates a new VTIMEZONE with that end time.
;; TODO set remaining properties, and type of the newly created component.
(define (extrapolate-tz-stream strm)
(let ((nevent (copy-vcomponent (stream-car strm))))
(set! (attr nevent 'DTSTART)
))
;; old code fails since (length standard) ≠ (length summer)
;; Also, it copies the summmer time, making the alternation
;; break (but that wasn't the primary problem)
#;
(let ((nevent (copy-vcomponent (stream-ref strm 1))))
(mod! (attr nevent 'DTSTART)
= (add-duration (time-difference
(attr (stream-ref strm 1) 'DTSTART)
(attr (stream-ref strm 0) 'DTSTART))))
(stream-append strm (stream nevent))))
;; The RFC requires that at least one DAYLIGHT or STANDARD component is present.
;; Any number of both can be present. This should handle all these cases well,
;; as long as noone has multiple overlapping timezones, which depend on some
;; further condition. That feels like something that should be impossible, but
;; this is (human) time we are talking about.
(define-public (make-tz-set tz)
(let ((strm (interleave-streams
ev-time<?
;; { DAYLIGHT, STANDARD }
(map generate-recurrence-set (children tz)))))
(cond [(stream-null? strm) stream-null]
[(stream-null? (stream-drop 2 strm))
(let ((strm (extrapolate-tz-stream strm)))
(stream-zip strm (stream-cdr strm)))]
[else (stream-zip strm (stream-cdr strm))])))
;; str ::= ±[0-9]{4}
;; str → int seconds
(define (parse-offset str)
(let* (((± h1 h0 m1 m0) (string->list str)))
((primitive-eval (symbol ±))
(+ (* 60 (string->number (string m1 m0)))
(* 60 60 (string->number (string h1 h0)))))))
;; Finds the VTIMEZONE with id @var{tzid} in calendar.
;; Crashes on error.
(define (find-tz cal tzid)
(let ((ret (find (lambda (tz) (string=? tzid (attr tz 'TZID)))
(filter (lambda (o) (eq? 'VTIMEZONE (type o)))
(children cal)))))
ret))
;; Takes a VEVENT.
;; Assumes that DTSTART has a TZID property, and that that TZID is available as
;; a direct child of the parent of @var{ev}.
(define-public (get-tz-offset ev)
(let ((ret (stream-find
(lambda (z)
(let* (((start end) (map (extract 'DTSTART) z)))
(and (time<=? start (attr ev 'DTSTART))
(time<? (attr ev 'DTSTART) end))))
(attr (find-tz (parent ev)
(car (prop (attr* ev 'DTSTART) 'TZID)))
'X-HNH-TZSET))))
(if (not ret)
0 (parse-offset (attr (car ret) 'TZOFFSETTO)))))
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