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(define-module (src 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))
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