cljs.reader/parse-and-validate-timestamp

(defn parse-and-validate-timestamp [s]
  (let [[_ years months days hours minutes seconds fraction offset-sign offset-hours offset-minutes :as v]
        (re-matches timestamp-regex s)]
    (if-not v
      (throw (js/Error. (str "Unrecognized date/time syntax: " s)))
      (let [years (parse-int years)
            months (or (parse-int months) 1)
            days (or (parse-int days) 1)
            hours (or (parse-int hours) 0)
            minutes (or (parse-int minutes) 0)
            seconds (or (parse-int seconds) 0)
            fraction (or (parse-int (zero-fill-right-and-truncate fraction 3)) 0)
            offset-sign (if (= offset-sign "-") -1 1)
            offset-hours (or (parse-int offset-hours) 0)
            offset-minutes (or (parse-int offset-minutes) 0)
            offset (* offset-sign (+ (* offset-hours 60) offset-minutes))]
        [years
         (check 1 months 12 "timestamp month field must be in range 1..12")
         (check 1 days (days-in-month months (leap-year? years)) "timestamp day field must be in range 1..last day in month")
         (check 0 hours 23 "timestamp hour field must be in range 0..23")
         (check 0 minutes 59 "timestamp minute field must be in range 0..59")
         (check 0 seconds (if (= minutes 59) 60 59) "timestamp second field must be in range 0..60")
         (check 0 fraction 999 "timestamp millisecond field must be in range 0..999")
         offset]))))