Major reordering in datetime.

1 files changed, 549 insertions, 553 deletions

diff --git a/module/datetime.scm b/module/datetime.scm
index 126695d1..a95eac47 100644
--- a/module/datetime.scm
+++ b/module/datetime.scm
@@ -19,6 +19,9 @@
   :re-export (locale-month)
   )
 
+
+;;; Enums
+
 (define-many define-public
   (jan january   ) 1
   (feb february  ) 2
@@ -31,8 +34,26 @@
   (sep september ) 9
   (oct october   ) 10
   (nov november  ) 11
-  (dec december  ) 12
-  )
+  (dec december  ) 12)
+
+(define-many define-public
+  (sun) 0
+  (mon) 1
+  (tue) 2
+  (wed) 3
+  (thu) 4
+  (fri) 5
+  (sat) 6)
+
+
+;;; Configuration
+
+(define-public week-start (make-parameter sun))
+
+(define-config week-start sun
+  "First day of week"
+  pre: (ensure (lambda (x) (<= sun x sat)))
+  post: week-start)
 
 
 ;;; RECORD TYPES
@@ -151,6 +172,15 @@
   (set (tz (tm->datetime (gmtime n)))
        "UTC"))
 
+
+;; this returns UTC time, with a TZ component set to "UTC"
+(define-public (current-datetime)
+  (unix-time->datetime ((@ (guile) current-time))))
+
+(define-public (current-date)
+  (get-date (current-datetime)))
+
+
 
 
 ;; datetime → datetime
@@ -169,9 +199,31 @@
       ;; strip tz-name, to conform with my local time.
       (set (tz (tm->datetime tm)) #f))))
 
+(define-public (as-date date/-time)
+  (cond [(datetime? date/-time) (get-date date/-time)]
+        [(date? date/-time) date/-time]
+        [(time? date/-time) (date)]
+        [else (error "Object not a date, time, or datetime object ~a" date/-time)]))
+
+(define-public (as-time date/-time)
+  (cond [(datetime? date/-time) (get-time% date/-time)]
+        [(date? date/-time) (time)]
+        [(time? date/-time) date/-time]
+        [else (error "Object not a date, time, or datetime object ~a" date/-time)]))
+
+(define-public (as-datetime dt)
+  (cond [(datetime? dt) dt]
+        [(date? dt) (datetime date: dt time: (time))]
+        [(time? dt) (datetime time: dt date: (date))]
+        [else (error "Object not a date, time, or datetime object ~a" dt)]))
+
 
 
-;;; UTIL
+(define-public (date-zero? date)
+  (= 0 (year date) (month date) (day date)))
+
+(define-public (time-zero? time)
+  (= 0 (hour time) (minute time) (second time)))
 
 ;; int -> bool
 (define-public (leap-year? year)
@@ -193,27 +245,506 @@
   (if (leap-year? (year date))
       366 365))
 
+(define-public (start-of-month date)
+  (set (day date) 1))
+
+(define-public (end-of-month date)
+  (set (day date) (days-in-month date)))
+
+(define-public (start-of-year date)
+  (set-> date
+         (day 1)
+         (month 1)))
+
+(define-public (date-stream date-increment start-day)
+  (stream-iterate (lambda (d) (date+ d date-increment))
+                  start-day))
+
+(define-public (day-stream start-day)
+  (date-stream (date day: 1) start-day))
+
+(define-public (month-stream start-day)
+  (date-stream (date month: 1) start-day))
+
+(define-public (week-stream start-day)
+  (date-stream (date day: 7) 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))
+
+(define-public (date-min a b)
+  (if (date< a b) a b))
+
+(define-public (date-max a b)
+  (if (date< a b) b a))
+
+(define-public (datetime-min a b)
+  (if (datetime< a b) a b))
+
+(define-public (datetime-max a b)
+  (if (datetime< a b) b a))
+
+(define*-public (month+ date-object #:optional (change 1))
+  (date+ date-object (date month: change)))
+
+(define*-public (month- date-object #:optional (change 1))
+  (date- date-object (date month: change)))
+
+;; 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)))))
+
+
+
+;; given a date, returns the date the first week of that year starts on.
+;; @example
+;; (week-1-start #2020-01-01 mon)
+;; ⇒ 2019-12-30
+;; @end example
+(define*-public (week-1-start d optional: (wkst (week-start)))
+  (let* ((ystart (start-of-year d))
+         (day-index (modulo (- (week-day ystart) wkst) 7)))
+    (if (> day-index 3)
+        (date+ ystart (date day: (- 7 day-index)))
+        (date- ystart (date day: day-index)))))
+
+;; (week-number #2020-01-01 mon) ; => 1
+;; (week-number #2019-12-31 mon) ; => 1
+(define*-public (week-number d optional: (wkst (week-start)))
+  ;; Calculating week number for starts of week was much simpler.
+  ;; We can both skip the special cases for Jan 1, 2 & 3. It also
+  ;; solved some weird bug that was here before.
+
+  (let ((d (start-of-week d wkst)))
+   (cond
+    [(and (= 12 (month d))
+          (memv (day d) '(29 30 31))
+          (< (year d) (year (date+ (start-of-week d wkst)
+                                   (date day: 3)))))
+     1]
+
+    [else
+     (let* ((w1-start (week-1-start d wkst))
+            (week day (floor/ (days-in-interval w1-start d)
+                              7)))
+       (1+ week))])))
+
+(define*-public (date-starting-week
+                 week-number d
+                 optional: (wkst (week-start)))
+  (date+ (week-1-start d wkst)
+         (date day: (* (1- week-number) 7))))
+
+
+(define*-public (week-day-name week-day-number optional: truncate-to
+                               key: (locale %global-locale))
+
+  ;; NOTE this allows days larger than 7 (sunday if counting from monday).
+  (let ((str (catch 'out-of-range
+               (lambda () (locale-day (1+ (modulo week-day-number 7)) locale))
+               (lambda (oor str num)
+                 (scm-error 'out-of-range 'week-day-name
+                            "~a == (~a % 7) + 1"
+                            (list num week-day-number)
+                            (list week-day-number))))))
+    ;; I also know about the @var{locale-day-short} method, but I need
+    ;; strings of length 2.
+    (if truncate-to
+        (string-take str truncate-to)
+        str)))
+
+
+;; @verbatim
+;;    A          B          C          D          E         ¬F
+;; |s1|     :     |s2| : |s1|     :     |s2| :          : |s1|
+;; |  |     :     |  | : |  ||s2| : |s1||  | : |s1||s2| : |  |
+;; |  ||s2| : |s1||  | : |  ||  | : |  ||  | : |  ||  | :
+;;     |  | : |  |     : |  ||  | : |  ||  | : |  ||  | :     |s2|
+;;     |  | : |  |     : |  |     :     |  | :          :     |  |
+;;
+;; Infinitely short ---+|s2| : |s1|+--- : two instants don't overlap
+;; events, overlap   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))))
+
+
+;; Returns the first instance of the given week-day after @var{d}.
+;; @example
+;; (find-first-week-day mon #2020-04-01)
+;; => #2020-04-06
+;; (find-first-week-day mon #2020-04-10)
+;; => #2020-04-13
+;; (find-first-week-day mon #2020-04-30)
+;; => #2020-05-04
+;; @end example
+(define-public (find-first-week-day wday d)
+  (let* ((start-day (week-day d))
+         (diff (- wday start-day)))
+    (date+ d (date day: (modulo diff 7)))))
+
+;; returns instances of the given week-day in month between
+;; month-date and end of month.
+;; @example
+;; (all-wday-in-month mon #2020-06-01)
+;; => (#2020-06-01 #2020-06-08 #2020-06-15 #2020-06-22 #2020-06-29)
+;; (all-wday-in-month mon #2020-06-10)
+;; => (#2020-06-15 #2020-06-22 #2020-06-29)
+;; @end example
+;; week-day, date → (list date)
+(define-public (all-wday-in-month wday month-date)
+  (stream->list
+   (stream-take-while
+    (lambda (d) (= (month d) (month month-date)))
+    (week-stream (find-first-week-day wday month-date)))))
+
+
+(define-public (all-wday-in-year wday year-date)
+  (stream->list
+   (stream-take-while
+    (lambda (d) (= (year d) (year year-date)))
+    (week-stream (find-first-week-day wday year-date)))))
+
+(define-public (add-day d)
+  (date+ d (date day: 1)))
+
+(define-public (remove-day d)
+  (date- d (date day: 1)))
+
+(define-public (in-date-range? start-date end-date)
+  (lambda (date)
+    (date<= start-date date end-date)))
+
+;; Returns a list of the seven week days, with @var{week-start}
+;; as the beginning of the week.
+;; @example
+;; (weekday-list sun)
+;; => (0 1 2 3 4 5 6)
+;; @end example
+(define-public (weekday-list week-start)
+  (take (drop (apply circular-list (iota 7))
+              week-start)
+        7))
+
+;; returns the date the week containing d started.
+;; (start-of-week #2020-04-02 sun) ; => 2020-03-29
+(define*-public (start-of-week d optional: (week-start (week-start)))
+  (date- d (date day: (modulo (- (week-day d)
+                                 week-start)
+                              7))))
+
+;; (end-of-week #2020-04-01 mon)
+;; => 2020-04-05
+(define*-public (end-of-week d optional: (week-start (week-start)))
+  (date+ (start-of-week d week-start)
+         (date day: 6)))
+
+
+;; Given a month and and which day the week starts on,
+;; returns three lists, which are:
+;; The days leading up to the current month, but share a week
+;; The days in the current month
+;; The days after the current month, but which shares a week.
+;; 
+;;       mars 2020
+;; må ti on to fr lö sö
+;;                    1
+;;  2  3  4  5  6  7  8
+;;  9 10 11 12 13 14 15
+;; 16 17 18 19 20 21 22
+;; 23 24 25 26 27 28 29
+;; 30 31
+;; @lisp
+;; (month-days #2020-03-01 mon)
+;; ; ⇒ (2020-02-24 ... 2020-02-29)
+;; ; ⇒ (2020-03-01 ... 2020-03-31)
+;; ; ⇒ (2020-04-01 ... 2020-04-05)
+;; @end lisp
+;; Ignores day component of @var{date}.
+(define*-public (month-days date optional: (week-start (week-start)))
+  (let* ((month-len (days-in-month date))
+         (prev-month-len (days-in-month (month- date)))
+         (month-start (modulo (- (week-day date) week-start) 7)))
+    (values
+     (map (lambda (d) (set (day (month- date)) d))
+          (iota month-start (1+ (- prev-month-len month-start))))
+     (map (lambda (d) (set (day date) d)) (iota month-len 1))
+     (map (lambda (d) (set (day (month+ date)) d))
+          (iota (modulo (- (* 7 5) month-len month-start) 7) 1)))))
+
+
+(define-public (days-in-interval start-date end-date)
+  (let ((diff (date-difference (date+ end-date (date day: 1)) start-date)))
+    (with-streams
+     (fold + (day diff)
+           (map days-in-month
+                (take (+ (month diff)
+                         (* 12 (year diff)))
+                      (month-stream start-date)))))))
+
+;; Day from start of the year, so 1 feb would be day 32.
+;; Also known as Julian day.
+(define-public (year-day date)
+  (days-in-interval (start-of-year date) date))
+
+
+;; @example
+;; (time->decimal-hour #10:30:00) ; => 10.5
+;; @end example
+(define-public (time->decimal-hour time)
+  (exact->inexact (+ (hour time)
+                     (/ (minute time) 60)
+                     (/ (second time) 3600))))
+
+(define*-public (datetime->decimal-hour dt optional: start-date)
+
+  (let ((date-diff
+         (cond [start-date
+                (let* ((end-date (date+ start-date (get-date dt))))
+                  (days-in-interval start-date end-date)) ]
+               [(or (not (zero? (month (get-date dt))))
+                    (not (zero? (year (get-date dt)))))
+                (error "Multi-month intervals only supported when start-date is given" dt)]
+               [else (day (get-date dt))])))
+    (+ (time->decimal-hour (get-time% dt))
+       (* (1- date-diff) 24))))
+
+;; Returns a list of all dates from start to end.
+;; both inclusive
+;; date, date → [list date]
+(define-public (date-range start end)
+  (stream->list
+   (stream-take-while (lambda (d) (date<= d end))
+                      (day-stream start))))
+
 
+;;; Output
 
-(define-public (as-date date/-time)
-  (cond [(datetime? date/-time) (get-date date/-time)]
-        [(date? date/-time) date/-time]
-        [(time? date/-time) (date)]
-        [else (error "Object not a date, time, or datetime object ~a" date/-time)]))
+(define*-public (datetime->string
+                 datetime
+                 optional: (fmt "~Y-~m-~dT~H:~M:~S")
+                 key: allow-unknown?)
+  (define date (get-date datetime))
+  (define time (get-time% datetime))
+  (with-output-to-string
+    (lambda ()
+      (fold (lambda (token state)
+              (case state
+                ((#\~)
+                 (case token
+                   ((#\~) (display "~"))
+                   ((#\H) (format #t "~2'0d" (hour time)))
+                   ((#\k) (format #t "~2' d" (hour time)))
+                   ((#\M) (format #t "~2'0d" (minute time)))
+                   ((#\S) (format #t "~2'0d" (second time)))
+                   ((#\Y) (format #t "~4'0d" (year date)))
+                   ((#\m) (format #t "~2'0d" (month date)))
+                   ((#\d) (format #t "~2'0d" (day date)))
+                   ;; Should be same as ~_d
+                   ((#\s) (display (datetime->unix-time datetime))) ; epoch time!
+                   ((#\e) (format #t "~2' d" (day date)))
+                   ((#\1) (format #t "~4'0d-~2'0d-~2'0d"
+                                  (year date) (month date) (day date)))
+                   ((#\3) (format #t "~2'0d:~2'0d:~2'0d"
+                                  (hour time) (minute time) (second time)))
+                   ((#\A) (display (week-day-name (week-day date))))
+                   ((#\a) (display (week-day-name (week-day date) 3)))
+                   ((#\b) (display (locale-month-short (month date))))
+                   ((#\B) (display (locale-month (month date))))
+                   ((#\Z) (when (equal? "UTC" (get-timezone datetime)) (display "Z")))
+                   (else (unless allow-unknown?
+                           (error 'datetime->string "Invalid format token ~a" token))))
+                 #f)
+                (else (unless (char=? #\~ token) (display token)) token)))
+            #f
+            (string->list fmt)))))
 
-(define-public (as-time date/-time)
-  (cond [(datetime? date/-time) (get-time% date/-time)]
-        [(date? date/-time) (time)]
-        [(time? date/-time) date/-time]
-        [else (error "Object not a date, time, or datetime object ~a" date/-time)]))
+(define*-public (date->string date
+                              optional: (fmt "~Y-~m-~d")
+                              key: allow-unknown?)
+  (datetime->string (datetime date: date)
+                    fmt allow-unknown?: allow-unknown?))
 
-(define-public (as-datetime dt)
-  (cond [(datetime? dt) dt]
-        [(date? dt) (datetime date: dt time: (time))]
-        [(time? dt) (datetime time: dt date: (date))]
-        [else (error "Object not a date, time, or datetime object ~a" dt)]))
+(define*-public (time->string time
+                              optional: (fmt "~H:~M:~S")
+                              key: allow-unknown?)
+  (datetime->string (datetime time: time)
+                    fmt allow-unknown?: allow-unknown?))
+
+
+
+;;; Input
+
+(define*-public (string->datetime str optional: (fmt "~Y-~m-~dT~H:~M:~S~Z"))
+  (let loop ((str (string->list str))
+             (fmt (string->list fmt))
+             (dt (datetime)))
+
+    (define time (get-time% dt))
+    (define date (get-date dt))
+    (define (as-dt dt)
+      (cond [(date? dt) (datetime date: dt time: time)]
+            [(time? dt) (datetime date: date time: dt)]
+            [else dt]))
+
+    (cond [(null? str)
+           ;; (warning  "Premature end of string")
+           dt]
+          [(null? fmt)
+           ;; (warning "Unsparsed characters at end of string")
+           dt]
+          [(eq? #\~ (car fmt))
+           (case (cadr fmt)
+             [(#\~) (if (eq? #\~ (car str))
+                        (loop (cdr str)
+                              (cddr fmt)
+                              dt)
+                        (error "Non-match"))]
+             [(#\Z)
+              (if (eq? #\Z (car str))
+                  (loop (cdr str)
+                        (cdr fmt)
+                        (set (tz dt) "UTC"))
+                  (loop str
+                        (cdr fmt)
+                        dt))]
+             [(#\H #\M #\S #\m #\d)
+              (let* ((pre post (split-at str 2))
+                     (num (-> pre list->string string->number)))
+                (loop
+                 post
+                 (cddr fmt)
+                 (as-dt
+                  (case (cadr fmt)
+                    [(#\H) (set (hour time)   num)]
+                    [(#\M) (set (minute time) num)]
+                    [(#\S) (set (second time) num)]
+                    [(#\m) (set (month date)  num)]
+                    [(#\d) (set (day date)    num)]))))]
+
+             [(#\Y)
+              (let* ((pre post (split-at str 4))
+                     (num (-> pre list->string string->number)))
+                (loop
+                 post
+                 (cddr fmt)
+                 (as-dt (set (year date) num))))]
+
+             [else
+              (error "Unimplemented or incorrect parse token")])]
+          [else
+           (if (eq? (car str) (car fmt))
+               (loop (cdr str)
+                     (cdr fmt)
+                     dt)
+               (error (format #f "Mismatched symbol, expected ~a got ~a"
+                              (car fmt) (car str))))])))
+
+(define*-public (string->time str optional: (fmt "~H:~M:~S"))
+  (get-time% (string->datetime str fmt)))
+
+(define*-public (string->date str optional: (fmt "~Y-~m-~d"))
+  (get-date (string->datetime str fmt)))
+
+
+(define-public (parse-ics-date str)
+  (string->date str "~Y~m~d"))
+
+(define-public (parse-ics-time str)
+  (string->time str "~H~M~S"))
+
+(define*-public (parse-ics-datetime str optional: zone)
+  (let ((dt (string->datetime str "~Y~m~dT~H~M~S~Z")))
+    (if (tz dt)
+        dt
+        (set (tz dt) zone))))
+
+(define-public (parse-iso-date str)
+  (string->date str))
+
+(define-public (parse-iso-time str)
+  (string->time str))
+
+(define-public (parse-iso-datetime str)
+  (string->datetime str))
+
+(define-public (parse-freeform-date str)
+  (parse-iso-datetime str))
+
+(define (date->sexp d)
+  `(date year: ,(year d)
+         month: ,(month d)
+         day: ,(day d)))
+
+(define (time->sexp t)
+  `(time hour: ,(hour t)
+         minute: ,(minute t)
+         second: ,(second t)))
+
+(define (datetime->sexp dt)
+  `(datetime date: ,(get-date dt)
+             time: ,(get-time% dt)
+             tz: ,(tz dt)))
+
+(define (date-reader chr port)
+  (unread-char chr port)
+  (let ((line (symbol->string (read port))))
+    (cond [(string-contains line "T")
+           (-> line string->datetime datetime->sexp)]
+          [(string-contains line ":")
+           (-> line string->time time->sexp)]
+          [(string-contains line "-")
+           (-> line string->date date->sexp)])))
+
+(read-hash-extend #\0 date-reader)
+(read-hash-extend #\1 date-reader)
+(read-hash-extend #\2 date-reader)
 
 
+;;; Everything below really messy
+
 ;;; EQUIALENCE
 
 (define-public (date= . args)
@@ -332,11 +863,6 @@
 
 ;;; OPERATIONS
 
-(define-public (date-zero? date)
-  (= 0 (year date) (month date) (day date)))
-
-(define-public (time-zero? time)
-  (= 0 (hour time) (minute time) (second time)))
 
 ;; TODO +1 month is weird for late days in a month.
 ;; is the last of january +1 month the last of february,
@@ -628,533 +1154,3 @@
                                             (date day: overflow))
                                      (get-date start))
               time: fixed-time)))
-
-
-
-;; this returns UTC time, with a TZ component set to "UTC"
-(define-public (current-datetime)
-  (unix-time->datetime ((@ (guile) current-time))))
-
-(define-public (current-date)
-  (get-date (current-datetime)))
-
-
-
-
-
-(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 (string->datetime str optional: (fmt "~Y-~m-~dT~H:~M:~S~Z"))
-  (let loop ((str (string->list str))
-             (fmt (string->list fmt))
-             (dt (datetime)))
-
-    (define time (get-time% dt))
-    (define date (get-date dt))
-    (define (as-dt dt)
-      (cond [(date? dt) (datetime date: dt time: time)]
-            [(time? dt) (datetime date: date time: dt)]
-            [else dt]))
-
-    (cond [(null? str)
-           ;; (warning  "Premature end of string")
-           dt]
-          [(null? fmt)
-           ;; (warning "Unsparsed characters at end of string")
-           dt]
-          [(eq? #\~ (car fmt))
-           (case (cadr fmt)
-             [(#\~) (if (eq? #\~ (car str))
-                        (loop (cdr str)
-                              (cddr fmt)
-                              dt)
-                        (error "Non-match"))]
-             [(#\Z)
-              (if (eq? #\Z (car str))
-                  (loop (cdr str)
-                        (cdr fmt)
-                        (set (tz dt) "UTC"))
-                  (loop str
-                        (cdr fmt)
-                        dt))]
-             [(#\H #\M #\S #\m #\d)
-              (let* ((pre post (split-at str 2))
-                     (num (-> pre list->string string->number)))
-                (loop
-                 post
-                 (cddr fmt)
-                 (as-dt
-                  (case (cadr fmt)
-                    [(#\H) (set (hour time)   num)]
-                    [(#\M) (set (minute time) num)]
-                    [(#\S) (set (second time) num)]
-                    [(#\m) (set (month date)  num)]
-                    [(#\d) (set (day date)    num)]))))]
-
-             [(#\Y)
-              (let* ((pre post (split-at str 4))
-                     (num (-> pre list->string string->number)))
-                (loop
-                 post
-                 (cddr fmt)
-                 (as-dt (set (year date) num))))]
-
-             [else
-              (error "Unimplemented or incorrect parse token")])]
-          [else
-           (if (eq? (car str) (car fmt))
-               (loop (cdr str)
-                     (cdr fmt)
-                     dt)
-               (error (format #f "Mismatched symbol, expected ~a got ~a"
-                              (car fmt) (car str))))])))
-
-(define*-public (string->time str optional: (fmt "~H:~M:~S"))
-  (get-time% (string->datetime str fmt)))
-
-(define*-public (string->date str optional: (fmt "~Y-~m-~d"))
-  (get-date (string->datetime str fmt)))
-
-
-
-(define-public (parse-ics-date str)
-  (string->date str "~Y~m~d"))
-
-(define-public (parse-ics-time str)
-  (string->time str "~H~M~S"))
-
-(define*-public (parse-ics-datetime str optional: zone)
-  (let ((dt (string->datetime str "~Y~m~dT~H~M~S~Z")))
-    (if (tz dt)
-        dt
-        (set (tz dt) zone))))
-
-(define-public (parse-iso-date str)
-  (string->date str))
-
-(define-public (parse-iso-time str)
-  (string->time str))
-
-(define-public (parse-iso-datetime str)
-  (string->datetime str))
-
-(define (date->sexp d)
-  `(date year: ,(year d)
-         month: ,(month d)
-         day: ,(day d)))
-
-(define (time->sexp t)
-  `(time hour: ,(hour t)
-         minute: ,(minute t)
-         second: ,(second t)))
-
-(define (datetime->sexp dt)
-  `(datetime date: ,(get-date dt)
-             time: ,(get-time% dt)
-             tz: ,(tz dt)))
-
-(define (date-reader chr port)
-  (unread-char chr port)
-  (let ((line (symbol->string (read port))))
-    (cond [(string-contains line "T")
-           (-> line string->datetime datetime->sexp)]
-          [(string-contains line ":")
-           (-> line string->time time->sexp)]
-          [(string-contains line "-")
-           (-> line string->date date->sexp)])))
-
-(read-hash-extend #\0 date-reader)
-(read-hash-extend #\1 date-reader)
-(read-hash-extend #\2 date-reader)
-
-
-
-
-
-(define-public (start-of-month date)
-  (set (day date) 1))
-
-(define-public (end-of-month date)
-  (set (day date) (days-in-month date)))
-
-(define-public (start-of-year date)
-  (set-> date
-         (day 1)
-         (month 1)))
-
-(define-public (date-stream date-increment start-day)
-  (stream-iterate (lambda (d) (date+ d date-increment))
-                  start-day))
-
-(define-public (day-stream start-day)
-  (date-stream (date day: 1) start-day))
-
-(define-public (month-stream start-day)
-  (date-stream (date month: 1) start-day))
-
-(define-public (week-stream start-day)
-  (date-stream (date day: 7) 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))
-
-(define-public (date-min a b)
-  (if (date< a b) a b))
-
-(define-public (date-max a b)
-  (if (date< a b) b a))
-
-(define-public (datetime-min a b)
-  (if (datetime< a b) a b))
-
-(define-public (datetime-max a b)
-  (if (datetime< a b) b a))
-
-(define*-public (month+ date-object #:optional (change 1))
-  (date+ date-object (date month: change)))
-
-(define*-public (month- date-object #:optional (change 1))
-  (date- date-object (date month: change)))
-
-;; 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-start (make-parameter sun))
-
-(define-config week-start sun
-  "First day of week"
-  pre: (ensure (lambda (x) (<= sun x sat)))
-  post: week-start)
-
-;; given a date, returns the date the first week of that year starts on.
-;; @example
-;; (week-1-start #2020-01-01 mon)
-;; ⇒ 2019-12-30
-;; @end example
-(define*-public (week-1-start d optional: (wkst (week-start)))
-  (let* ((ystart (start-of-year d))
-         (day-index (modulo (- (week-day ystart) wkst) 7)))
-    (if (> day-index 3)
-        (date+ ystart (date day: (- 7 day-index)))
-        (date- ystart (date day: day-index)))))
-
-;; (week-number #2020-01-01 mon) ; => 1
-;; (week-number #2019-12-31 mon) ; => 1
-(define*-public (week-number d optional: (wkst (week-start)))
-  ;; Calculating week number for starts of week was much simpler.
-  ;; We can both skip the special cases for Jan 1, 2 & 3. It also
-  ;; solved some weird bug that was here before.
-
-  (let ((d (start-of-week d wkst)))
-   (cond
-    [(and (= 12 (month d))
-          (memv (day d) '(29 30 31))
-          (< (year d) (year (date+ (start-of-week d wkst)
-                                   (date day: 3)))))
-     1]
-
-    [else
-     (let* ((w1-start (week-1-start d wkst))
-            (week day (floor/ (days-in-interval w1-start d)
-                              7)))
-       (1+ week))])))
-
-(define*-public (date-starting-week
-                 week-number d
-                 optional: (wkst (week-start)))
-  (date+ (week-1-start d wkst)
-         (date day: (* (1- week-number) 7))))
-
-
-(define*-public (week-day-name week-day-number optional: truncate-to
-                               key: (locale %global-locale))
-
-  ;; NOTE this allows days larger than 7 (sunday if counting from monday).
-  (let ((str (catch 'out-of-range
-               (lambda () (locale-day (1+ (modulo week-day-number 7)) locale))
-               (lambda (oor str num)
-                 (scm-error 'out-of-range 'week-day-name
-                            "~a == (~a % 7) + 1"
-                            (list num week-day-number)
-                            (list week-day-number))))))
-    ;; I also know about the @var{locale-day-short} method, but I need
-    ;; strings of length 2.
-    (if truncate-to
-        (string-take str truncate-to)
-        str)))
-
-(define*-public (datetime->string
-                 datetime
-                 optional: (fmt "~Y-~m-~dT~H:~M:~S")
-                 key: allow-unknown?)
-  (define date (get-date datetime))
-  (define time (get-time% datetime))
-  (with-output-to-string
-    (lambda ()
-      (fold (lambda (token state)
-              (case state
-                ((#\~)
-                 (case token
-                   ((#\~) (display "~"))
-                   ((#\H) (format #t "~2'0d" (hour time)))
-                   ((#\k) (format #t "~2' d" (hour time)))
-                   ((#\M) (format #t "~2'0d" (minute time)))
-                   ((#\S) (format #t "~2'0d" (second time)))
-                   ((#\Y) (format #t "~4'0d" (year date)))
-                   ((#\m) (format #t "~2'0d" (month date)))
-                   ((#\d) (format #t "~2'0d" (day date)))
-                   ;; Should be same as ~_d
-                   ((#\s) (display (datetime->unix-time datetime))) ; epoch time!
-                   ((#\e) (format #t "~2' d" (day date)))
-                   ((#\1) (format #t "~4'0d-~2'0d-~2'0d"
-                                  (year date) (month date) (day date)))
-                   ((#\3) (format #t "~2'0d:~2'0d:~2'0d"
-                                  (hour time) (minute time) (second time)))
-                   ((#\A) (display (week-day-name (week-day date))))
-                   ((#\a) (display (week-day-name (week-day date) 3)))
-                   ((#\b) (display (locale-month-short (month date))))
-                   ((#\B) (display (locale-month (month date))))
-                   ((#\Z) (when (equal? "UTC" (get-timezone datetime)) (display "Z")))
-                   (else (unless allow-unknown?
-                           (error 'datetime->string "Invalid format token ~a" token))))
-                 #f)
-                (else (unless (char=? #\~ token) (display token)) token)))
-            #f
-            (string->list fmt)))))
-
-(define*-public (date->string date
-                              optional: (fmt "~Y-~m-~d")
-                              key: allow-unknown?)
-  (datetime->string (datetime date: date)
-                    fmt allow-unknown?: allow-unknown?))
-
-(define*-public (time->string time
-                              optional: (fmt "~H:~M:~S")
-                              key: allow-unknown?)
-  (datetime->string (datetime time: time)
-                    fmt allow-unknown?: allow-unknown?))
-
-
-;; @verbatim
-;;    A          B          C          D          E         ¬F
-;; |s1|     :     |s2| : |s1|     :     |s2| :          : |s1|
-;; |  |     :     |  | : |  ||s2| : |s1||  | : |s1||s2| : |  |
-;; |  ||s2| : |s1||  | : |  ||  | : |  ||  | : |  ||  | :
-;;     |  | : |  |     : |  ||  | : |  ||  | : |  ||  | :     |s2|
-;;     |  | : |  |     : |  |     :     |  | :          :     |  |
-;;
-;; Infinitely short ---+|s2| : |s1|+--- : two instants don't overlap
-;; events, overlap   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)))
-
-(define-public (in-date-range? start-date end-date)
-  (lambda (date)
-    (date<= start-date date end-date)))
-
-;; Returns a list of the seven week days, with @var{week-start}
-;; as the beginning of the week.
-;; @example
-;; (weekday-list sun)
-;; => (0 1 2 3 4 5 6)
-;; @end example
-(define-public (weekday-list week-start)
-  (take (drop (apply circular-list (iota 7))
-              week-start)
-        7))
-
-;; returns the date the week containing d started.
-;; (start-of-week #2020-04-02 sun) ; => 2020-03-29
-(define*-public (start-of-week d optional: (week-start (week-start)))
-  (date- d (date day: (modulo (- (week-day d)
-                                 week-start)
-                              7))))
-
-;; (end-of-week #2020-04-01 mon)
-;; => 2020-04-05
-(define*-public (end-of-week d optional: (week-start (week-start)))
-  (date+ (start-of-week d week-start)
-         (date day: 6)))
-
-
-;; Given a month and and which day the week starts on,
-;; returns three lists, which are:
-;; The days leading up to the current month, but share a week
-;; The days in the current month
-;; The days after the current month, but which shares a week.
-;; 
-;;       mars 2020
-;; må ti on to fr lö sö
-;;                    1
-;;  2  3  4  5  6  7  8
-;;  9 10 11 12 13 14 15
-;; 16 17 18 19 20 21 22
-;; 23 24 25 26 27 28 29
-;; 30 31
-;; @lisp
-;; (month-days #2020-03-01 mon)
-;; ; ⇒ (2020-02-24 ... 2020-02-29)
-;; ; ⇒ (2020-03-01 ... 2020-03-31)
-;; ; ⇒ (2020-04-01 ... 2020-04-05)
-;; @end lisp
-;; Ignores day component of @var{date}.
-(define*-public (month-days date optional: (week-start (week-start)))
-  (let* ((month-len (days-in-month date))
-         (prev-month-len (days-in-month (month- date)))
-         (month-start (modulo (- (week-day date) week-start) 7)))
-    (values
-     (map (lambda (d) (set (day (month- date)) d))
-          (iota month-start (1+ (- prev-month-len month-start))))
-     (map (lambda (d) (set (day date) d)) (iota month-len 1))
-     (map (lambda (d) (set (day (month+ date)) d))
-          (iota (modulo (- (* 7 5) month-len month-start) 7) 1)))))
-
-
-
-
-(define-public (days-in-interval start-date end-date)
-  (let ((diff (date-difference (date+ end-date (date day: 1)) start-date)))
-    (with-streams
-     (fold + (day diff)
-           (map days-in-month
-                (take (+ (month diff)
-                         (* 12 (year diff)))
-                      (month-stream start-date)))))))
-
-;; Day from start of the year, so 1 feb would be day 32.
-;; Also known as Julian day.
-(define-public (year-day date)
-  (days-in-interval (start-of-year date) date))
-
-
-;; @example
-;; (time->decimal-hour #10:30:00) ; => 10.5
-;; @end example
-(define-public (time->decimal-hour time)
-  (exact->inexact (+ (hour time)
-                     (/ (minute time) 60)
-                     (/ (second time) 3600))))
-
-(define*-public (datetime->decimal-hour dt optional: start-date)
-
-  (let ((date-diff
-         (cond [start-date
-                (let* ((end-date (date+ start-date (get-date dt))))
-                  (days-in-interval start-date end-date)) ]
-               [(or (not (zero? (month (get-date dt))))
-                    (not (zero? (year (get-date dt)))))
-                (error "Multi-month intervals only supported when start-date is given" dt)]
-               [else (day (get-date dt))])))
-    (+ (time->decimal-hour (get-time% dt))
-       (* (1- date-diff) 24))))
-
-;; Returns a list of all dates from start to end.
-;; both inclusive
-;; date, date → [list date]
-(define-public (date-range start end)
-  (stream->list
-   (stream-take-while (lambda (d) (date<= d end))
-                      (day-stream start))))
-
-
-
-;; Returns the first instance of the given week-day after @var{d}.
-;; @example
-;; (find-first-week-day mon #2020-04-01)
-;; => #2020-04-06
-;; (find-first-week-day mon #2020-04-10)
-;; => #2020-04-13
-;; (find-first-week-day mon #2020-04-30)
-;; => #2020-05-04
-;; @end example
-(define-public (find-first-week-day wday d)
-  (let* ((start-day (week-day d))
-         (diff (- wday start-day)))
-    (date+ d (date day: (modulo diff 7)))))
-
-;; returns instances of the given week-day in month between
-;; month-date and end of month.
-;; @example
-;; (all-wday-in-month mon #2020-06-01)
-;; => (#2020-06-01 #2020-06-08 #2020-06-15 #2020-06-22 #2020-06-29)
-;; (all-wday-in-month mon #2020-06-10)
-;; => (#2020-06-15 #2020-06-22 #2020-06-29)
-;; @end example
-;; week-day, date → (list date)
-(define-public (all-wday-in-month wday month-date)
-  (stream->list
-   (stream-take-while
-    (lambda (d) (= (month d) (month month-date)))
-    (week-stream (find-first-week-day wday month-date)))))
-
-
-(define-public (all-wday-in-year wday year-date)
-  (stream->list
-   (stream-take-while
-    (lambda (d) (= (year d) (year year-date)))
-    (week-stream (find-first-week-day wday year-date)))))