From 7ce6d0091dd52979f51684a16162e9d771ec835d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@hornquist.se>
Date: Sat, 2 Mar 2019 23:14:53 +0100
Subject: Start work on recuring events.

---
 vcalendar/recur.scm | 155 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 vcalendar/recur.scm

(limited to 'vcalendar')

diff --git a/vcalendar/recur.scm b/vcalendar/recur.scm
new file mode 100644
index 00000000..474d228d
--- /dev/null
+++ b/vcalendar/recur.scm
@@ -0,0 +1,155 @@
+(define-module (vcalendar recur)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-9 gnu)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-41)
+
+  #:use-module (vcalendar)
+  )
+
+(define s "FREQ=WEEKLY;UNTIL=20191130")
+
+(define (generate-kv-pairs str)
+  (map (cut string-split <> #\=)
+       (string-split str #\;)))
+
+(define upstring->symbol (compose string->symbol string-upcase))
+
+(define-syntax-rule (ensure key val test)
+  ((key)
+   (let ((v val))
+     (if (test v)
+         v
+         (throw 'bad-value key val))
+     )))
+
+#;
+(let ((key 'FREQ)
+      (val-base 'HOURLY))
+  (case key
+    (FREQ (upstring->symbol val-base)
+          (memv <> '(SECONDLY MINUTELY HOURLY DAILY
+                           WEEKLY MONTHLY YEARLY)))))
+
+(define-immutable-record-type <recur-rule>
+  (make-recur-rules freq until count interval)
+  recur-rule?
+  (freq get-freq set-freq)
+  (until get-until set-until)
+  (count get-count set-count)
+  (interval get-interval set-interval)))
+
+(let ((s->n string->number))
+ (reduce (lambda (kv rule)
+        (let ((key (upstring->symbol (car kv)))
+              (val-base (cadr kv)))
+          (case key
+            ((FREQ)
+             (set-freq rule
+                       (ensure (upstring->symbol val-base)
+                               (cut memv <>
+                                    '(SECONDLY MINUTELY HOURLY DAILY
+                                               WEEKLY MONTHLY YEARLY)))))
+            
+
+            ((UNTIL)
+             (set-until rule (parse-datetime val-base)))
+
+            ((COUNT) (set-count rule (s->n val-base)))
+
+            ((INTERVAL) (set-internal rule (s->n val-base)))
+
+            ((BYSECOND) (let ((s (s->n val-base)))
+                          (<= 0 s 60)))
+
+            ((BYMINUTE) (let ((m (s->n val-base)))
+                          (<= 0 m 59)))
+
+            ((BYHOUR) (let ((h (s->n val-base)))
+                        (<= 0 h 23)))
+            
+            #|
+            ((BYDAY) #; TODO )
+
+            ((BYMONTHDAY) #; TODO)
+            ((BYYEARDAY)  )
+            ((BYWEEKNO)  )
+            ((BYMONTH)  )
+            ((BYSETPOS) )
+            ((WKST)  )
+            |#
+            (else 'err))))
+
+      (generate-kv-pairs s)))
+
+
+
+#|
+Each recuring event should be expanded to a stream of all it's occurances.
+
+The first instance of the event is at DTSTART,
+times for following instances are calculating according to the DSL below. 
+     
+3.3.10. Recurrence Rule
+     Value Name: RECUR
+|#
+
+
+#|
+       byseclist   = ( seconds *("," seconds) )
+
+       seconds     = 1*2DIGIT       ;0 to 60
+
+       byminlist   = ( minutes *("," minutes) )
+
+       minutes     = 1*2DIGIT       ;0 to 59
+
+       byhrlist    = ( hour *("," hour) )
+
+       hour        = 1*2DIGIT       ;0 to 23
+
+       bywdaylist  = ( weekdaynum *("," weekdaynum) )
+
+       weekdaynum  = [[±] ordwk] weekday
+
+       ordwk       = 1*2DIGIT       ;1 to 53
+
+       weekday     = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
+       ;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
+       ;FRIDAY, and SATURDAY days of the week.
+
+
+
+Desruisseaux                Standards Track                    [Page 39]
+
+RFC 5545                       iCalendar                  September 2009
+
+
+       bymodaylist = ( monthdaynum *("," monthdaynum) )
+
+       monthdaynum = [±] ordmoday
+
+       ordmoday    = 1*2DIGIT       ;1 to 31
+
+       byyrdaylist = ( yeardaynum *("," yeardaynum) )
+
+       yeardaynum  = [±] ordyrday
+
+       ordyrday    = 1*3DIGIT      ;1 to 366
+
+       bywknolist  = ( weeknum *("," weeknum) )
+
+       weeknum     = [±] ordwk
+
+       bymolist    = ( monthnum *("," monthnum) )
+
+       monthnum    = 1*2DIGIT       ;1 to 12
+
+       bysplist    = ( setposday *("," setposday) )
+
+       setposday   = yeardaynum
+
+
+
+|#
-- 
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