Elm.Native.Time = function(elm) {
  'use strict';

  var Signal = Elm.Signal(elm);
  var Maybe = Elm.Maybe(elm);

  function fpsWhen(desiredFPS, isOn) {
    var msPerFrame = 1000 / desiredFPS;
    var prev = Date.now(), curr = prev, diff = 0, wasOn = true;
    var ticker = Signal.constant(diff);
    function tick(zero) { return function() {
        curr = Date.now();
	diff = zero ? 0 : curr - prev;
	prev = curr;
	elm.notify(ticker.id, diff);
      };
    }
    var timeoutID = 0;
    function f(isOn, t) {
      if (isOn) {
        timeoutID = setTimeout(tick(!wasOn && isOn), msPerFrame);
      } else if (wasOn) {
	clearTimeout(timeoutID);	    
      }
      wasOn = isOn;
      return t;
    }
    return A3( Signal.lift2, F2(f), isOn, ticker );
  }
 
  function everyWhen(t, isOn) {
    var clock = Signal.constant(Date.now());
    function tellTime() { elm.notify(clock.id, Date.now()); }
    setInterval(tellTime, t);
    return clock;
  }

  function since(t, s) {
    function cmp(a,b) { return !Value.eq(a,b) }
    var dcount = Signal.count(Signal.delay(t)(s));
    return A3( Signal.lift2, F2(cmp), Signal.count(s), dcount );
  }
  function after(t) {
      t *= 1000;
      var thread = Signal.constant(false);
      setTimeout(function() { elm.notify(thread.id, true); }, t);
      return thread;
  }
  function before(t) {
      t *= 1000;
      var thread = Signal.constant(true);
      setTimeout(function() { elm.notify(thread.id, false); }, t);
      return thread;
  }
  function read(s) {
      var t = Date.parse(s);
      return isNaN(t) ? Maybe.Nothing : Maybe.Just(t);
  }
  return elm.Native.Time = {
      fpsWhen : F2(fpsWhen),
      fps : function(t) { return fpsWhen(t, Signal.constant(true)); },
      every : function(t) { return everyWhen(t, Signal.constant(true)) },
      delay : Signal.delay,
      since : F2(since),
      after  : after,
      before : before,
      toDate : function(t) { return new window.Date(t); },
      read   : read
  };

};