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(define-module (vcalendar timezone)
:use-module (vcalendar)
: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 ((vcalendar recur) :select (generate-recurrence-set))
:use-module ((vcalendar datetime) :select (ev-time<?))
)
;;@begin exampe
;; <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
;; 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)))))
(if (stream-null? strm)
stream-null
(stream-zip strm (stream-cdr strm)))))
(define (parse-offset str)
(let* (((pm h1 h0 m1 m0) (string->list str)))
((primitive-eval (symbol pm))
(+ (* 60 (string->number (list->string (list m1 m0))))
(* 60 60 (string->number (list->string (list 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)))
(children cal 'VTIMEZONE))))
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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