/*  */

var uid = 0;

/**

 * A dep is an observable that can have multiple

 * directives subscribing to it.

 */

var Dep = function Dep () {

  this.id = uid++;

  this.subs = [];

};

Dep.prototype.addSub = function addSub (sub) {

  this.subs.push(sub);

};

Dep.prototype.removeSub = function removeSub (sub) {

  remove(this.subs, sub);

};

Dep.prototype.depend = function depend () {

  if (Dep.target) {

    Dep.target.addDep(this);

  }

};

Dep.prototype.notify = function notify () {

  // stabilize the subscriber list first

  var subs = this.subs.slice();

  for (var i = 0, l = subs.length; i < l; i++) {

    subs[i].update();

  }

};

// the current target watcher being evaluated.

// this is globally unique because there could be only one

// watcher being evaluated at any time.

Dep.target = null;

var targetStack = [];

function pushTarget (_target) {

  if (Dep.target) { targetStack.push(Dep.target); }

  Dep.target = _target;

}

function popTarget () {

  Dep.target = targetStack.pop();

}

/*  */