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(define-module (vcomponent recurrence parse)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-19) ; Datetime
#:use-module (srfi srfi-19 util)
#:use-module (srfi srfi-26)
#:use-module ((vcomponent datetime) #:select (parse-datetime))
#:duplicates (last) ; Replace @var{count}
#:use-module (vcomponent recurrence internal)
#:use-module (util)
#:use-module (ice-9 match)
#:export (parse-recurrence-rule))
;; @example
;; <weekday> ∈ weekdays
;; <weekdaynum> ::= [[±] <num>] <weekday> ;; +3MO
;; (<weekadynum>, ...)
;; @end example
;; Returns a pair, where the @code{car} is the offset
;; and @code{cdr} is the day symbol.
;; The @code{car} may be @code{#f}.
(define (parse-day-spec str)
(let* ((numchars (append '(#\+ #\-) (map integer->char (iota 10 #x30))))
(num symb (span (cut memv <> numchars)
(string->list str))))
(cons (string->number (list->string num))
(apply symbol symb))))
(define-macro (quick-case key . cases)
(let ((else-clause (or (assoc-ref cases 'else)
'(error "Guard failed"))))
`(case ,key
,@(map (match-lambda
((key guard '=> body ...)
`((,key) (if (not ,guard)
(begin ,@else-clause)
(begin ,@body))))
((key body ...)
`((,key) (begin ,@body)))
(('else body ...)
`(else ,@body)))
cases))))
(define (parse-recurrence-rule str)
(fold
(lambda (kv o)
(let* (((key val) kv))
(let-lazy
((symb (string->symbol val))
(date (date->time-utc (parse-datetime val)))
(days (map parse-day-spec (string-split val #\,)))
(num (string->number val))
(nums (map string->number (string-split val #\,))))
(quick-case (string->symbol key)
(UNTIL (set! (until o) date))
(COUNT (<= 0 num) => (set! (count o) num))
(INTERVAL (<= 0 num) => (set! (interval o) num))
(FREQ (memv symb intervals) => (set! (freq o) symb))
(WKST (memv symb weekdays) => (set! (wkst o) symb))
(BYSECOND (every (lambda (n) (<= 0 n 60)) nums) => (set! (bysecond o) nums))
(BYMINUTE (every (lambda (n) (<= 0 n 59)) nums) => (set! (byminute o) nums))
(BYHOUR (every (lambda (n) (<= 0 n 23)) nums) => (set! (byhour o) nums))
(BYMONTH (every (lambda (n) (<= 1 n 12)) nums) => (set! (byweekno o) nums))
(BYDAY (every (lambda (p) (memv (cdr p) weekdays)) days) => (set! (byday o) days))
(BYMONTHDAY (every (lambda (n) (and (!= n 0) (<= -31 n 31))) nums) => (set! (bymonthday o) nums))
(BYYEARDAY (every (lambda (n) (and (!= n 0) (<= -366 n 366))) nums) => (set! (byyearday o) nums))
(BYSETPOS (every (lambda (n) (and (!= n 0) (<= -366 n 366))) nums) => (set! (bysetpos o) nums))
(BYWEEKNO (every (lambda (n) (and (!= n 0) (<= -53 n 53))) nums) => (set! (byweekno o) nums))
(else o)))))
;; obj
(make-recur-rule 1 'MO)
;; ((key val) ...)
(map (cut string-split <> #\=)
(string-split str #\;))))
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