From ecb92a54a8c2dce5f60765f3dece4223b9ff856a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Thu, 21 Mar 2019 21:19:50 +0100
Subject: Fixed recurrence code.

---
 vcalendar/recurrence/generate.scm | 108 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 vcalendar/recurrence/generate.scm

(limited to 'vcalendar/recurrence/generate.scm')

diff --git a/vcalendar/recurrence/generate.scm b/vcalendar/recurrence/generate.scm
new file mode 100644
index 00000000..222362fd
--- /dev/null
+++ b/vcalendar/recurrence/generate.scm
@@ -0,0 +1,108 @@
+(define-module (vcalendar recurrence generate)
+  ;; #:use-module (srfi srfi-1)
+  ;; #:use-module (srfi srfi-9 gnu)        ; Records
+  #: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 control)          ; ?
+  #:use-module (ice-9 match)
+  #:use-module (vcalendar)
+  #:use-module (vcalendar datetime)
+  #:use-module (util)
+
+  #: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 interval)
+  (case interval
+    ((SECONDLY) 1)
+    ((MINUTELY) 60)
+    ((HOURLY) (* 60 60))
+    ((DAILY) (* 60 60 24))
+    ((WEEKLY) (* 60 60 24 7))))
+
+(define-stream (recur-event-stream event rule-obj)
+  (stream-unfold
+   ;; Rule → event
+   (match-lambda
+     ((last r)
+      (let ((e (copy-vcomponent last)))   ; new event
+        ;; TODO
+        ;; Update DTEND as (add-duration DTSTART DURATINO)
+        (cond
+
+         ;; BYDAY and the like depend on the freq?
+         ;; Line 7100
+         ;; Table @ 2430
+
+         ((memv (freq r) '(SECONDLY MINUTELY HOURLY DAILY WEEKLY))
+          (mod! (attr e "DTSTART")
+                (cut add-duration! <>
+                     (make-duration
+                      ;; INTERVAL
+                      (* (interval r)
+                         (seconds-in (freq r)))))))
+
+         ((memv (freq r) '(MONTHLY YEARLY))
+          ;; Hur fasen beräkrnar man det här!!!!
+          #f
+          )
+
+         (else #f))
+        e)))
+
+   ;; Rule → Bool (#t if continue, #f if stop)
+   (match-lambda
+     ((last r)
+
+      ;; (optional->bool
+      ;;  (do (<$> (cut time<=? (attr last 'DTSTART)) (until r))
+      ;;      (<$> (negate zero?) (count r))
+      ;;    (just #t)))
+
+      (or (and (not (until r)) (not (count r)))
+          (and=> (until r) (cut time<=? (attr last 'DTSTART) <>)) ; UNTIL
+          (and=> (count r) (negate zero?)))                      ; COUNT
+
+      )
+     )
+
+   ;; Rule → (next) Rule
+   (match-lambda
+     ((last r)
+      ;; Note that this doesn't modify, since r is immutable.
+      (list last
+            (if (count r)
+                (mod! (count r) 1-)
+                r))))
+   (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 (build-recur-rules (attr event "RRULE"))))
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