(ns hnparser.rate-limit)

(defn now
  []
  (/ (System/currentTimeMillis) 1000)) ; working in seconds seems simpler

(defn rate-limit-creator
  [rate per]
  (let [allowed (ref rate) last-access (ref (now))]
    (fn [& more]
      (dosync
       (let [current-time (now) time-passed (- current-time @last-access)]
     (ref-set allowed
          (let [allow (+ @allowed (* time-passed (/ rate per)))]
            (if (> allow rate) ; make sure not to make the bucket
              rate             ; larger than the allowed rate
              allow)))
     (ref-set last-access current-time)
     (if (>= @allowed 1) ; I'm doing the rest outside the doysnc
         (do             ; to avoid thunks and side effects
           (ref-set allowed (dec @allowed))
           [true]) ; about to estimate the time till were within capacity
         [false (/ (* (- 1 @allowed) rate) per)]))))))

(defn rate-limit
  [func rate per retry]
  (let [rate-limiter (rate-limit-creator rate per)]
    (fn [& args]
      (let [throttler (rate-limiter)]
    (if (first throttler)
      (apply func args)
      (if retry
        (do ; convert from seconds to milliseconds
          (. Thread sleep (* 1000 (second throttler)))
          (recur args))))))))

(defmacro defrlf ; must.. hide.. complexity..
  [name func rate per retry]
  `(def ~name (rate-limit ~func ~rate ~per ~retry)))