Elm.Touch = function() {

  function Dict() {
    this.keys = [];
    this.values = [];

    this.insert = function(key,value) {
      this.keys.push(key);
      this.values.push(value);
    };
    this.lookup = function(key) {
      var i = this.keys.indexOf(key)
      return i >= 0 ? this.values[i] : {x:0,y:0,t:0};
    };
    this.remove = function(key) {
      var i = this.keys.indexOf(key);
      if (i < 0) return;
      var t = this.values[i];
      this.keys.splice(i,1);
      this.values.splice(i,1);
      return t;
    };
  }

  var root = Elm.Signal.constant([]),
      tapTime = 500,
      hasTap = false,
      tap = {_:[true],x:[0],y:[0]},
      dict = new Dict();

  function touch(t) {
      var r = dict.lookup(t.identifier);
      return {_ : [true], id: [t.identifier],
	      x: [t.pageX], y: [t.pageY],
	      x0: [r.x], y0: [r.y],
	      t0: [r.t] };
  }

  function start(e) {
    dict.insert(e.identifier,{x:e.pageX,y:e.pageY,t:Date.now()});
  }
  function end(e) {
    var t = dict.remove(e.identifier);
    if (Date.now() - t.t < tapTime) {
	hasTap = true;
	tap = {_:[true], x:[t.x], y:[t.y]};
    }
  }

  function listen(name, f) {
    function update(e) {
      for (var i = e.changedTouches.length; i--; ) { f(e.changedTouches[i]); }
      var ts = new Array(e.touches.length);
      for (var i = e.touches.length; i--; ) { ts[i] = touch(e.touches[i]); }
      var hasListener = Dispatcher.notify(root.id, ts);
      if (!hasListener) return document.removeEventListener(name, update);
      e.preventDefault();
    }
    Value.addListener(document, name, update);
  }

  listen("touchstart", start);
  listen("touchmove", function(_){});
  listen("touchend", end);
  listen("touchcancel", end);
  listen("touchleave", end);

  function dependency(f) {
      var sig = Elm.Signal.lift(f)(root);
      root.defaultNumberOfKids += 1;
      sig.defaultNumberOfKids = 0;
      return sig;
  }

  var touches = dependency(function(ts) {
	  return Elm.JavaScript.castJSArrayToList(ts);
      });
  var taps = function() {
      var sig = dependency(function(_) { return tap; });
      sig.defaultNumberOfKids = 1;
      function pred(_) { var b = hasTap; hasTap = false; return b; }
      var sig2 =  Elm.Signal.keepIf(pred)({_:[true],x:[0],y:[0]})(sig);
      sig2.defaultNumberOfKids = 0;
      return sig2;
  }();

  return { touches: touches, taps: taps };
}();