From 3d7e1cf403961d03bb08af1332c8226c0b0cef6d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@hornquist.se>
Date: Tue, 18 Feb 2020 02:03:55 +0100
Subject: Freed datetime from its srfi-19 prison.

---
 module/datetime/util.scm | 167 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 167 insertions(+)
 create mode 100644 module/datetime/util.scm

(limited to 'module/datetime')

diff --git a/module/datetime/util.scm b/module/datetime/util.scm
new file mode 100644
index 00000000..0eaf484a
--- /dev/null
+++ b/module/datetime/util.scm
@@ -0,0 +1,167 @@
+(define-module (datetime util)
+  :use-module (datetime)
+  :use-module ((srfi srfi-1) :select (fold))
+  :use-module (srfi srfi-26)
+  :use-module (srfi srfi-41)
+  :use-module (util)
+  )
+
+(define-public (start-of-month date)
+  (set (day date) 1))
+
+
+(define-public (parse-freeform-date str)
+  (let* (((year month day) (map string->number (string-split str #\-))))
+    (date year: year month: month day: day)
+    ))
+
+(define-public (day-stream start-day)
+  (stream-iterate (cut date+ <> #0-0-1)
+                  start-day))
+
+(define-public (month-stream start-day)
+  (stream-iterate (cut date+ <> #0-1-0)
+                  start-day))
+
+(define-public (time-min a b)
+  (if (time<? a b) a b))
+
+(define-public (time-max a b)
+  (if (time<? a b) b a))
+
+
+;; https://projecteuclid.org/euclid.acta/1485888738
+;; 1. Begel.
+;; J sei die Zahl des Jahrhunderts,
+;; K die Jahrszahl innerhalb desselben,
+;; m die Zahl des Monats,
+;; q die Zahl des Monatstags,
+;; h die Zahl des Wochentags;
+(define (zeller J K m q)
+  (modulo (+ q
+             (floor-quotient (* 13 (1+ m))
+                             5)
+             K
+             (floor-quotient K 4)
+             5
+             (- J))
+          7))
+
+;; 0 indexed, starting at sunday.
+(define-public (week-day date)
+  (let* ((J K (floor/ (year date) 100))
+         (m (month date)))
+    (if (memv m '(1 2))
+        (zeller J (1- K) (+ m 12) (day date))
+        (zeller J K (month date) (day date)))))
+
+(define-many define-public
+  (sun) 0
+  (mon) 1
+  (tue) 2
+  (wed) 3
+  (thu) 4
+  (fri) 5
+  (sat) 6
+  )
+
+(define-public (week-day-name week-day-number)
+  ;; TODO internationalization
+  (case* week-day-number
+         [(sun 7) "Sön"]
+         [(mon) "Mån"]
+         [(tue) "Tis"]
+         [(wed) "Ons"]
+         [(thu) "Tor"]
+         [(fri) "Fre"]
+         [(sat) "Lör"]))
+
+(define*-public (date->string date optional: (fmt "~Y-~m-~d") key: allow-unknown?)
+  (with-output-to-string
+    (lambda ()
+      (fold (lambda (token state)
+              (case state
+                ((#\~)
+                 (case token
+                   ((#\~) (display "~"))
+                   ((#\Y) (format #t "~4'0d" (year date)))
+                   ((#\m) (format #t "~2'0d" (month date)))
+                   ((#\d) (format #t "~2'0d" (day date)))
+                   ((#\1) (format #t "~4'0d-~2'0d-~2'0d"
+                                  (year date) (month date) (day date)))
+                   ((#\a) (display (week-day-name (week-day date))))
+                   (else (unless allow-unknown?
+                           (error 'date->string "Invalid format token ~a" token))))
+                 #f)
+                (else (unless (char=? #\~ token) (display token)) token)))
+            #f
+            (string->list fmt)))))
+
+(define*-public (time->string time optional: (fmt "~H:~M:~S") key: allow-unknown?)
+  (with-output-to-string
+    (lambda ()
+      (fold (lambda (token state)
+              (case state
+                ((#\~)
+                 (case token
+                   ((#\~) (display "~"))
+                   ((#\H) (format #t "~2'0d" (hour time)))
+                   ((#\M) (format #t "~2'0d" (minute time)))
+                   ((#\S) (format #t "~2'0d" (second time)))
+                   ;; ((#\z) (when (utc? time) (display "Z")))
+                   (else (unless allow-unknown?
+                           (error 'time->string "Invalid format token ~a" token))))
+                 #f)
+                (else (unless (char=? #\~ token) (display token)) token)))
+            #f
+            (string->list fmt)))))
+
+
+
+
+;; @verbatim
+;;    A          B          C          D          E         ¬F
+;; |s1|     :     |s2| : |s1|     :     |s2| :          : |s1|
+;; |  |     :     |  | : |  ||s2| : |s1||  | : |s1||s2| : |  |
+;; |  ||s2| : |s1||  | : |  ||  | : |  ||  | : |  ||  | :
+;;     |  | : |  |     : |  ||  | : |  ||  | : |  ||  | :     |s2|
+;;     |  | : |  |     : |  |     :     |  | :          :     |  |
+;; @end verbatim
+;; 
+;; E is covered by both case A and B.
+(define-public (timespan-overlaps? s1-begin s1-end s2-begin s2-end)
+  "Return whetever or not two timespans overlap."
+  (or
+   ;; A
+   (and (date/-time<? s2-begin s1-end)
+        (date/-time<? s1-begin s2-end))
+
+   ;; B
+   (and (date/-time<? s1-begin s2-end)
+        (date/-time<? s2-begin s1-end))
+
+   ;; C
+   (and (date/-time<? s1-begin s2-begin)
+        (date/-time<? s2-end s1-end))
+
+   ;; D
+   (and (date/-time<? s2-begin s1-begin)
+        (date/-time<? s1-end s2-end))))
+
+(define-public (add-day d)
+  (date+ d (date day: 1)))
+
+(define-public (remove-day d)
+  (date- d (date day: 1)))
+
+
+;; Checks if @var{datetime} is within the date
+;; given by @var{base-date}.
+;; TODO test time zones
+;; date x datetime → bool
+;; (define-public (in-day? base-date date/-time)
+;;   (date< base-date (as-date date/-time) (date+ base-date (date day: 1))))
+
+(define-public (in-date-range? start-date end-date)
+  (lambda (date)
+    (date<= start-date date end-date)))
-- 
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