konami_code.cljs

(defn on-konami-code []
  (prn :konami-code-detected))

(defn setup-konami-code-listener! []
  (let
   [key
    {37 :left
     38 :up
     39 :right
     40 :down
     65 :a
     66 :b}
    ; note: intentionally missing first up because last-at will block first valid key
    code [:up :down :down :left :right :left :right :b :a]
    max-delay 1500
    valid-keys (set (vals key))
    buffer (atom [])
    last-at (atom 0)
    tick #(reset! last-at (js/Date.))
    reset
    (fn []
      (reset! buffer [])
      (tick))]
   (js/document.addEventListener
    "keyup"
    (fn [^js e]
      (let [k (key (.-keyCode e))]
        (if (and (valid-keys k)
                 (<= (- (js/Date.) @last-at) max-delay))
          (do
            (tick)
            (swap! buffer conj k)
            (when (= (take-last (count code) @buffer)
                     code)
              (#'on-konami-code)))
          (reset)))))))