core.clj

(ns circuito.core
  (:require [clojure.core.async :as async :refer :all])
  (:gen-class))

(def ^:dynamic *timeout* 300)

;; Like defn, but executes body in a go block, allowing at most *timeout* milliseconds for completion
(defmacro defcommand [name args & body]
  `(defn ~name ~args
     (let [t# (timeout *timeout*)
           c# (chan)]
       (go (>! c# (do ~@body)))
       (<!! (go
             (let [[r# ch#] (alts! [t# c#])]
               (if (= ch# t#) :timeout r#)))))))

(defcommand fetch-url
  [url]
  (slurp url))

(defn- to-int
  "Tries to coerce a value to an integer"
  [val]
  (when val
    (cond (integer? val) val
          (number? val) (int val)
          (string? val) (int (Integer/parseInt val)))))

(defn -main
  "Fetch the URL in the first arg in second arg (or default) milliseconds"
  [& args]
  (let [uri (first args)
        t (or (to-int (second args)) *timeout*)]
    (binding [*timeout* t]
      (println
       (fetch-url uri)))))