ok

info.rkt

@@ -0,0 +1,20 @@
+#lang info
+
+(define pkg-authors '(hnmdijkema))
+(define version "0.1.0")
+(define license 'Apache-2.0)
+(define pkg-desc "A few utility functions around the gregor date module")
+
+(define scribblings
+  '(
+    ("scribblings/gregor-utils.scrbl" () (library) "gregor-utils")
+    )
+  )
+
+(define deps
+  '("base" "gregor"))
+
+(define build-deps
+  '("racket-doc"
+    "rackunit-lib"
+    "scribble-lib"))

main.rkt

@@ -0,0 +1,80 @@
+(module gregor-utils racket/base
+  (require (prefix-in g: gregor)
+           (prefix-in g: gregor/time)
+           tzinfo
+           racket/string
+           )
+
+  (provide date->moment
+           moment->date
+           racket-date?
+           )
+
+  (define (date*->moment dt)
+    (unless (date*? dt)
+      (error "dt must be of type date*"))
+    ;; As date* will be localtime or UTC, we're working
+    ;; with what we got. We can recognize UTC, but the
+    ;; timezone name will be something OS specific, e.g.
+    ;; on a dutch windows system: West-Europa (zomertijd)
+    ;; which is reported e.g. by windows powershell command
+    ;; get-timezone:
+    ;;
+    ;; Id                         : W. Europe Standard Time
+    ;; DisplayName                : (UTC+01:00) Amsterdam, Berlijn, Bern, Rome, Stockholm, Wenen
+    ;; StandardName               : West-Europa (standaardtijd)
+    ;; DaylightName               : West-Europa (zomertijd)
+    ;; BaseUtcOffset              : 01:00:00
+    ;; SupportsDaylightSavingTime : True
+    ;;
+    ;; but, as the racket standard date functions only
+    ;; work with UTC and localtime, we can request the current timezone
+    ;; tzinfo's (system-tzid) for localtime
+    ;; and use UTC for univeral time.
+    (let ((dt-tz (string-downcase (string-trim (date*-time-zone-name dt)))))
+      (g:moment (date-year dt)
+                (date-month dt)
+                (date-day dt)
+                (date-hour dt)
+                (date-minute dt)
+                (date-second dt)
+                (date*-nanosecond dt)
+                #:tz (if (string=? dt-tz "utc")
+                         "UTC"
+                         (system-tzid))
+                )
+      )
+    )
+
+  (define (date->moment dt)
+    (if (date*? dt)
+        (date*->moment dt)
+        (g:moment (date-year dt)
+                  (date-month dt)
+                  (date-day dt)
+                  (date-hour dt)
+                  (date-minute dt)
+                  (date-second dt)
+                  #:tz (date-time-zone-offset dt)))
+    )
+
+  (define (moment->date m)
+    (make-date* (g:->seconds m)
+               (g:->minutes m)
+               (g:->hours m)
+               (g:->day m)
+               (g:->month m)
+               (g:->year m)
+               (g:->wday m)
+               (g:->yday m)
+               #f
+               (g:->utc-offset m)
+               0
+               (g:->timezone m)
+               )
+    )
+
+  (define (racket-date? dt)
+    (date? dt))
+
+  ); end of module

scribblings/gregor-utils.scrbl

@@ -0,0 +1,60 @@
+#lang scribble/manual
+
+@(require
+   scribble/example
+   scribble/core
+   (for-label racket/base
+              racket/string
+              ))
+
+(define myeval
+   (make-base-eval '(require gregor gregor-utils)))
+
+@title[#:tag "gregor-utils"]{Some utility functions around the gregor date module}
+
+@author[@author+email["Hans Dijkema" "hans@dijkewijk.nl"]]
+
+@defmodule[gregor-utils]{This module provides some utility functions around the gregor date module}
+
+@section{Utility functions}
+
+@defproc[(date->moment [dt (or/c date? date*?)]) moment?]{
+  Converts a racket @racket{date} or @racket{date*} structure to a gregor @racket{moment}.
+  When it converts, it will assumes two kinds of dates.
+
+ @itemlist[
+     @item{The first being a standard racket date structure with a time zone offset.}
+     @item{The second for a date* structure, that will hold a named local timezone or 'UTC'.}
+     ]
+
+ This function will check if the date* structure is UTC time or local timezone. If it is
+ local timezone, it will use the function @racket{(system-tzid)} of tzinfo to determine the
+ local timezone id, that can be used to create a new gregor @racket{moment}.
+
+ As date* will be either localtime or UTC, we're working with what we got. We can recognize UTC, but the
+ timezone name will be something OS specific, e.g. on a dutch windows system: "West-Europa (zomertijd)".
+ This is reported e.g. in the windows powershell command:
+
+@#reader scribble/comment-reader
+[racketblock
+> get-timezone:
+
+  Id                         : W. Europe Standard Time
+  DisplayName                : (UTC+01:00) Amsterdam, Berlijn, Bern, Rome, Stockholm, Wenen
+  StandardName               : West-Europa (standaardtijd)
+  DaylightName               : West-Europa (zomertijd)
+  BaseUtcOffset              : 01:00:00
+  SupportsDaylightSavingTime : True
+]
+
+But, as the racket standard date functions only work with UTC and localtime, we can request the current timezone
+tzinfo's @racket{(system-tzid)} for localtime and use UTC for univeral time.
+}
+
+@defproc[(moment->date [m moment?]) date*?]{
+  Converts a gregor @racket{moment} to a standard racket @racket{date*}.
+}
+
+@defproc[(racket-date? [d any/c?]) boolean?]{
+  Returns #t, if d is of racket's standard type @racket{date} or racket{date*}.
+}