API: move `src` to `ss`

1 files changed, 44 insertions, 0 deletions

diff --git a/ss/dates.scm b/ss/dates.scm
new file mode 100644
index 0000000..58a1ec6
--- /dev/null
+++ b/ss/dates.scm
@@ -0,0 +1,44 @@
+(define-module (ss dates)
+  #:use-module (ice-9 format)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-19)
+  #:export (string/ISO->date
+            date->string/RFC3339
+            unix-date
+            newest
+            find-newest
+            date>?))
+
+(define (string/ISO->date string)
+  (string->date string "~Y-~m-~d"))
+
+(define (date->string/RFC3339 date)
+  (call-with-output-string
+    (lambda (p)
+      (let* ((offset           (abs (date-zone-offset date)))
+             (rem-h-seconds    (modulo offset (* 60 60)))
+             (offset-hours     (floor (/ (- offset rem-h-seconds) 60 60)))
+             (rem-m-seconds    (modulo rem-h-seconds 60))
+             (offset-minutes   (floor (/ (- rem-h-seconds rem-m-seconds) 60))))
+       (format
+         p
+         "~4,'0d-~2,'0d-~2,'0dT~2,'0d:~2,'0d:~2,'0d~:[Z~;~c~2,'0d:~2,'0d~]"
+         (date-year date)
+         (date-month date)
+         (date-day date)
+         (date-hour date)
+         (date-minute date)
+         (date-second date)
+         (not (= 0 (date-zone-offset date)))
+         (if (< 0 (date-zone-offset date)) #\+ #\-)
+         offset-hours
+         offset-minutes)))))
+
+(define unix-date (string/ISO->date "1970-01-01"))
+
+(define (newest a b) (if (time>? (date->time-utc a) (date->time-utc b)) a b))
+
+(define (date>? a b)
+  (time>? (date->time-utc a) (date->time-utc b)))
+
+(define (find-newest dates) (reduce newest unix-date dates))