'use strict';

/**
 * DESIGN NOTES
 *
 * The design decisions behind the scope are heavily favored for speed and memory consumption.
 *
 * The typical use of scope is to watch the expressions, which most of the time return the same
 * value as last time so we optimize the operation.
 *
 * Closures construction is expensive in terms of speed as well as memory:
 *   - No closures, instead use prototypical inheritance for API
 *   - Internal state needs to be stored on scope directly, which means that private state is
 *     exposed as $$____ properties
 *
 * Loop operations are optimized by using while(count--) { ... }
 *   - this means that in order to keep the same order of execution as addition we have to add
 *     items to the array at the beginning (shift) instead of at the end (push)
 *
 * Child scopes are created and removed often
 *   - Using an array would be slow since inserts in middle are expensive so we use linked list
 *
 * There are few watches then a lot of observers. This is why you don't want the observer to be
 * implemented in the same way as watch. Watch requires return of initialization function which
 * are expensive to construct.
 */


/**
 * @ngdoc object
 * @name ng.$rootScopeProvider
 * @description
 *
 * Provider for the $rootScope service.
 */

/**
 * @ngdoc function
 * @name ng.$rootScopeProvider#digestTtl
 * @methodOf ng.$rootScopeProvider
 * @description
 *
 * Sets the number of `$digest` iterations the scope should attempt to execute before giving up and assuming that the model is unstable.
 *
 * The current default is 10 iterations.
 *
 * In complex applications it's possible that the dependencies between `$watch`s will result in several digest iterations.
 * However if an application needs more than the default 10 digest iterations for its model to stabilize then you should investigate what is causing the model to continuously change during the digest.
 *
 * Increasing the TTL could have performance implications, so you should not change it without proper justification.
 *
 * @param {number} limit The number of digest iterations.
 */


/**
 * @ngdoc object
 * @name ng.$rootScope
 * @description
 *
 * Every application has a single root {@link ng.$rootScope.Scope scope}.
 * All other scopes are descendant scopes of the root scope. Scopes provide separation
 * between the model and the view, via a mechanism for watching the model for changes.
 * They also provide an event emission/broadcast and subscription facility. See the
 * {@link guide/scope developer guide on scopes}.
 */
function $RootScopeProvider(){
  var TTL = 10;
  var $rootScopeMinErr = minErr('$rootScope');

  this.digestTtl = function(value) {
    if (arguments.length) {
      TTL = value;
    }
    return TTL;
  };

  this.$get = ['$injector', '$exceptionHandler', '$parse', '$browser',
      function( $injector,   $exceptionHandler,   $parse,   $browser) {

    /**
     * @ngdoc function
     * @name ng.$rootScope.Scope
     *
     * @description
     * A root scope can be retrieved using the {@link ng.$rootScope $rootScope} key from the
     * {@link AUTO.$injector $injector}. Child scopes are created using the
     * {@link ng.$rootScope.Scope#methods_$new $new()} method. (Most scopes are created automatically when
     * compiled HTML template is executed.)
     *
     * Here is a simple scope snippet to show how you can interact with the scope.
     * <pre>
     * <file src="./test/ng/rootScopeSpec.js" tag="docs1" />
     * </pre>
     *
     * # Inheritance
     * A scope can inherit from a parent scope, as in this example:
     * <pre>
         var parent = $rootScope;
         var child = parent.$new();

         parent.salutation = "Hello";
         child.name = "World";
         expect(child.salutation).toEqual('Hello');

         child.salutation = "Welcome";
         expect(child.salutation).toEqual('Welcome');
         expect(parent.salutation).toEqual('Hello');
     * </pre>
     *
     *
     * @param {Object.<string, function()>=} providers Map of service factory which need to be provided
     *     for the current scope. Defaults to {@link ng}.
     * @param {Object.<string, *>=} instanceCache Provides pre-instantiated services which should
     *     append/override services provided by `providers`. This is handy when unit-testing and having
     *     the need to override a default service.
     * @returns {Object} Newly created scope.
     *
     */
    function Scope() {
      this.$id = nextUid();
      this.$$phase = this.$parent = this.$$watchers =
                     this.$$nextSibling = this.$$prevSibling =
                     this.$$childHead = this.$$childTail = null;
      this['this'] = this.$root =  this;
      this.$$destroyed = false;
      this.$$asyncQueue = [];
      this.$$postDigestQueue = [];
      this.$$listeners = {};
      this.$$isolateBindings = {};
    }

    /**
     * @ngdoc property
     * @name ng.$rootScope.Scope#$id
     * @propertyOf ng.$rootScope.Scope
     * @returns {number} Unique scope ID (monotonically increasing alphanumeric sequence) useful for
     *   debugging.
     */


    Scope.prototype = {
      constructor: Scope,
      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$new
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Creates a new child {@link ng.$rootScope.Scope scope}.
       *
       * The parent scope will propagate the {@link ng.$rootScope.Scope#$digest $digest()} and
       * {@link ng.$rootScope.Scope#$digest $digest()} events. The scope can be removed from the scope
       * hierarchy using {@link ng.$rootScope.Scope#$destroy $destroy()}.
       *
       * {@link ng.$rootScope.Scope#$destroy $destroy()} must be called on a scope when it is desired for
       * the scope and its child scopes to be permanently detached from the parent and thus stop
       * participating in model change detection and listener notification by invoking.
       *
       * @param {boolean} isolate If true, then the scope does not prototypically inherit from the
       *         parent scope. The scope is isolated, as it can not see parent scope properties.
       *         When creating widgets, it is useful for the widget to not accidentally read parent
       *         state.
       *
       * @returns {Object} The newly created child scope.
       *
       */
      $new: function(isolate) {
        var Child,
            child;

        if (isolate) {
          child = new Scope();
          child.$root = this.$root;
          // ensure that there is just one async queue per $rootScope and its children
          child.$$asyncQueue = this.$$asyncQueue;
          child.$$postDigestQueue = this.$$postDigestQueue;
        } else {
          Child = function() {}; // should be anonymous; This is so that when the minifier munges
            // the name it does not become random set of chars. This will then show up as class
            // name in the debugger.
          Child.prototype = this;
          child = new Child();
          child.$id = nextUid();
        }
        child['this'] = child;
        child.$$listeners = {};
        child.$parent = this;
        child.$$watchers = child.$$nextSibling = child.$$childHead = child.$$childTail = null;
        child.$$prevSibling = this.$$childTail;
        if (this.$$childHead) {
          this.$$childTail.$$nextSibling = child;
          this.$$childTail = child;
        } else {
          this.$$childHead = this.$$childTail = child;
        }
        return child;
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$watch
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Registers a `listener` callback to be executed whenever the `watchExpression` changes.
       *
       * - The `watchExpression` is called on every call to {@link ng.$rootScope.Scope#$digest $digest()} and
       *   should return the value that will be watched. (Since {@link ng.$rootScope.Scope#$digest $digest()}
       *   reruns when it detects changes the `watchExpression` can execute multiple times per
       *   {@link ng.$rootScope.Scope#$digest $digest()} and should be idempotent.)
       * - The `listener` is called only when the value from the current `watchExpression` and the
       *   previous call to `watchExpression` are not equal (with the exception of the initial run,
       *   see below). The inequality is determined according to
       *   {@link angular.equals} function. To save the value of the object for later comparison, the
       *   {@link angular.copy} function is used. It also means that watching complex options will
       *   have adverse memory and performance implications.
       * - The watch `listener` may change the model, which may trigger other `listener`s to fire. This
       *   is achieved by rerunning the watchers until no changes are detected. The rerun iteration
       *   limit is 10 to prevent an infinite loop deadlock.
       *
       *
       * If you want to be notified whenever {@link ng.$rootScope.Scope#$digest $digest} is called,
       * you can register a `watchExpression` function with no `listener`. (Since `watchExpression`
       * can execute multiple times per {@link ng.$rootScope.Scope#$digest $digest} cycle when a change is
       * detected, be prepared for multiple calls to your listener.)
       *
       * After a watcher is registered with the scope, the `listener` fn is called asynchronously
       * (via {@link ng.$rootScope.Scope#$evalAsync $evalAsync}) to initialize the
       * watcher. In rare cases, this is undesirable because the listener is called when the result
       * of `watchExpression` didn't change. To detect this scenario within the `listener` fn, you
       * can compare the `newVal` and `oldVal`. If these two values are identical (`===`) then the
       * listener was called due to initialization.
       *
       *
       * # Example
       * <pre>
           // let's assume that scope was dependency injected as the $rootScope
           var scope = $rootScope;
           scope.name = 'misko';
           scope.counter = 0;

           expect(scope.counter).toEqual(0);
           scope.$watch('name', function(newValue, oldValue) { scope.counter = scope.counter + 1; });
           expect(scope.counter).toEqual(0);

           scope.$digest();
           // no variable change
           expect(scope.counter).toEqual(0);

           scope.name = 'adam';
           scope.$digest();
           expect(scope.counter).toEqual(1);
       * </pre>
       *
       *
       *
       * @param {(function()|string)} watchExpression Expression that is evaluated on each
       *    {@link ng.$rootScope.Scope#$digest $digest} cycle. A change in the return value triggers a
       *    call to the `listener`.
       *
       *    - `string`: Evaluated as {@link guide/expression expression}
       *    - `function(scope)`: called with current `scope` as a parameter.
       * @param {(function()|string)=} listener Callback called whenever the return value of
       *   the `watchExpression` changes.
       *
       *    - `string`: Evaluated as {@link guide/expression expression}
       *    - `function(newValue, oldValue, scope)`: called with current and previous values as parameters.
       *
       * @param {boolean=} objectEquality Compare object for equality rather than for reference.
       * @returns {function()} Returns a deregistration function for this listener.
       */
      $watch: function(watchExp, listener, objectEquality) {
        var scope = this,
            get = compileToFn(watchExp, 'watch'),
            array = scope.$$watchers,
            watcher = {
              fn: listener,
              last: initWatchVal,
              get: get,
              exp: watchExp,
              eq: !!objectEquality
            };

        // in the case user pass string, we need to compile it, do we really need this ?
        if (!isFunction(listener)) {
          var listenFn = compileToFn(listener || noop, 'listener');
          watcher.fn = function(newVal, oldVal, scope) {listenFn(scope);};
        }

        if (typeof watchExp == 'string' && get.constant) {
          var originalFn = watcher.fn;
          watcher.fn = function(newVal, oldVal, scope) {
            originalFn.call(this, newVal, oldVal, scope);
            arrayRemove(array, watcher);
          };
        }

        if (!array) {
          array = scope.$$watchers = [];
        }
        // we use unshift since we use a while loop in $digest for speed.
        // the while loop reads in reverse order.
        array.unshift(watcher);

        return function() {
          arrayRemove(array, watcher);
        };
      },


      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$watchCollection
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Shallow watches the properties of an object and fires whenever any of the properties change
       * (for arrays, this implies watching the array items; for object maps, this implies watching the properties).
       * If a change is detected, the `listener` callback is fired.
       *
       * - The `obj` collection is observed via standard $watch operation and is examined on every call to $digest() to
       *   see if any items have been added, removed, or moved.
       * - The `listener` is called whenever anything within the `obj` has changed. Examples include adding, removing,
       *   and moving items belonging to an object or array.
       *
       *
       * # Example
       * <pre>
          $scope.names = ['igor', 'matias', 'misko', 'james'];
          $scope.dataCount = 4;

          $scope.$watchCollection('names', function(newNames, oldNames) {
            $scope.dataCount = newNames.length;
          });

          expect($scope.dataCount).toEqual(4);
          $scope.$digest();

          //still at 4 ... no changes
          expect($scope.dataCount).toEqual(4);

          $scope.names.pop();
          $scope.$digest();

          //now there's been a change
          expect($scope.dataCount).toEqual(3);
       * </pre>
       *
       *
       * @param {string|Function(scope)} obj Evaluated as {@link guide/expression expression}. The expression value
       *    should evaluate to an object or an array which is observed on each
       *    {@link ng.$rootScope.Scope#$digest $digest} cycle. Any shallow change within the collection will trigger
       *    a call to the `listener`.
       *
       * @param {function(newCollection, oldCollection, scope)} listener a callback function that is fired with both
       *    the `newCollection` and `oldCollection` as parameters.
       *    The `newCollection` object is the newly modified data obtained from the `obj` expression and the
       *    `oldCollection` object is a copy of the former collection data.
       *    The `scope` refers to the current scope.
       *
       * @returns {function()} Returns a de-registration function for this listener. When the de-registration function
       * is executed, the internal watch operation is terminated.
       */
      $watchCollection: function(obj, listener) {
        var self = this;
        var oldValue;
        var newValue;
        var changeDetected = 0;
        var objGetter = $parse(obj);
        var internalArray = [];
        var internalObject = {};
        var oldLength = 0;

        function $watchCollectionWatch() {
          newValue = objGetter(self);
          var newLength, key;

          if (!isObject(newValue)) {
            if (oldValue !== newValue) {
              oldValue = newValue;
              changeDetected++;
            }
          } else if (isArrayLike(newValue)) {
            if (oldValue !== internalArray) {
              // we are transitioning from something which was not an array into array.
              oldValue = internalArray;
              oldLength = oldValue.length = 0;
              changeDetected++;
            }

            newLength = newValue.length;

            if (oldLength !== newLength) {
              // if lengths do not match we need to trigger change notification
              changeDetected++;
              oldValue.length = oldLength = newLength;
            }
            // copy the items to oldValue and look for changes.
            for (var i = 0; i < newLength; i++) {
              if (oldValue[i] !== newValue[i]) {
                changeDetected++;
                oldValue[i] = newValue[i];
              }
            }
          } else {
            if (oldValue !== internalObject) {
              // we are transitioning from something which was not an object into object.
              oldValue = internalObject = {};
              oldLength = 0;
              changeDetected++;
            }
            // copy the items to oldValue and look for changes.
            newLength = 0;
            for (key in newValue) {
              if (newValue.hasOwnProperty(key)) {
                newLength++;
                if (oldValue.hasOwnProperty(key)) {
                  if (oldValue[key] !== newValue[key]) {
                    changeDetected++;
                    oldValue[key] = newValue[key];
                  }
                } else {
                  oldLength++;
                  oldValue[key] = newValue[key];
                  changeDetected++;
                }
              }
            }
            if (oldLength > newLength) {
              // we used to have more keys, need to find them and destroy them.
              changeDetected++;
              for(key in oldValue) {
                if (oldValue.hasOwnProperty(key) && !newValue.hasOwnProperty(key)) {
                  oldLength--;
                  delete oldValue[key];
                }
              }
            }
          }
          return changeDetected;
        }

        function $watchCollectionAction() {
          listener(newValue, oldValue, self);
        }

        return this.$watch($watchCollectionWatch, $watchCollectionAction);
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$digest
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Processes all of the {@link ng.$rootScope.Scope#$watch watchers} of the current scope and its children.
       * Because a {@link ng.$rootScope.Scope#$watch watcher}'s listener can change the model, the
       * `$digest()` keeps calling the {@link ng.$rootScope.Scope#$watch watchers} until no more listeners are
       * firing. This means that it is possible to get into an infinite loop. This function will throw
       * `'Maximum iteration limit exceeded.'` if the number of iterations exceeds 10.
       *
       * Usually, you don't call `$digest()` directly in
       * {@link ng.directive:ngController controllers} or in
       * {@link ng.$compileProvider#methods_directive directives}.
       * Instead, you should call {@link ng.$rootScope.Scope#$apply $apply()} (typically from within a
       * {@link ng.$compileProvider#methods_directive directives}), which will force a `$digest()`.
       *
       * If you want to be notified whenever `$digest()` is called,
       * you can register a `watchExpression` function with {@link ng.$rootScope.Scope#$watch $watch()}
       * with no `listener`.
       *
       * In unit tests, you may need to call `$digest()` to simulate the scope life cycle.
       *
       * # Example
       * <pre>
           var scope = ...;
           scope.name = 'misko';
           scope.counter = 0;

           expect(scope.counter).toEqual(0);
           scope.$watch('name', function(newValue, oldValue) {
             scope.counter = scope.counter + 1;
           });
           expect(scope.counter).toEqual(0);

           scope.$digest();
           // no variable change
           expect(scope.counter).toEqual(0);

           scope.name = 'adam';
           scope.$digest();
           expect(scope.counter).toEqual(1);
       * </pre>
       *
       */
      $digest: function() {
        var watch, value, last,
            watchers,
            asyncQueue = this.$$asyncQueue,
            postDigestQueue = this.$$postDigestQueue,
            length,
            dirty, ttl = TTL,
            next, current, target = this,
            watchLog = [],
            logIdx, logMsg, asyncTask;

        beginPhase('$digest');

        do { // "while dirty" loop
          dirty = false;
          current = target;

          while(asyncQueue.length) {
            try {
              asyncTask = asyncQueue.shift();
              asyncTask.scope.$eval(asyncTask.expression);
            } catch (e) {
              $exceptionHandler(e);
            }
          }

          do { // "traverse the scopes" loop
            if ((watchers = current.$$watchers)) {
              // process our watches
              length = watchers.length;
              while (length--) {
                try {
                  watch = watchers[length];
                  // Most common watches are on primitives, in which case we can short
                  // circuit it with === operator, only when === fails do we use .equals
                  if (watch && (value = watch.get(current)) !== (last = watch.last) &&
                      !(watch.eq
                          ? equals(value, last)
                          : (typeof value == 'number' && typeof last == 'number'
                             && isNaN(value) && isNaN(last)))) {
                    dirty = true;
                    watch.last = watch.eq ? copy(value) : value;
                    watch.fn(value, ((last === initWatchVal) ? value : last), current);
                    if (ttl < 5) {
                      logIdx = 4 - ttl;
                      if (!watchLog[logIdx]) watchLog[logIdx] = [];
                      logMsg = (isFunction(watch.exp))
                          ? 'fn: ' + (watch.exp.name || watch.exp.toString())
                          : watch.exp;
                      logMsg += '; newVal: ' + toJson(value) + '; oldVal: ' + toJson(last);
                      watchLog[logIdx].push(logMsg);
                    }
                  }
                } catch (e) {
                  $exceptionHandler(e);
                }
              }
            }

            // Insanity Warning: scope depth-first traversal
            // yes, this code is a bit crazy, but it works and we have tests to prove it!
            // this piece should be kept in sync with the traversal in $broadcast
            if (!(next = (current.$$childHead || (current !== target && current.$$nextSibling)))) {
              while(current !== target && !(next = current.$$nextSibling)) {
                current = current.$parent;
              }
            }
          } while ((current = next));

          if(dirty && !(ttl--)) {
            clearPhase();
            throw $rootScopeMinErr('infdig',
                '{0} $digest() iterations reached. Aborting!\nWatchers fired in the last 5 iterations: {1}',
                TTL, toJson(watchLog));
          }
        } while (dirty || asyncQueue.length);

        clearPhase();

        while(postDigestQueue.length) {
          try {
            postDigestQueue.shift()();
          } catch (e) {
            $exceptionHandler(e);
          }
        }
      },


      /**
       * @ngdoc event
       * @name ng.$rootScope.Scope#$destroy
       * @eventOf ng.$rootScope.Scope
       * @eventType broadcast on scope being destroyed
       *
       * @description
       * Broadcasted when a scope and its children are being destroyed.
       *
       * Note that, in AngularJS, there is also a `$destroy` jQuery event, which can be used to
       * clean up DOM bindings before an element is removed from the DOM.
       */

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$destroy
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Removes the current scope (and all of its children) from the parent scope. Removal implies
       * that calls to {@link ng.$rootScope.Scope#$digest $digest()} will no longer
       * propagate to the current scope and its children. Removal also implies that the current
       * scope is eligible for garbage collection.
       *
       * The `$destroy()` is usually used by directives such as
       * {@link ng.directive:ngRepeat ngRepeat} for managing the
       * unrolling of the loop.
       *
       * Just before a scope is destroyed, a `$destroy` event is broadcasted on this scope.
       * Application code can register a `$destroy` event handler that will give it a chance to
       * perform any necessary cleanup.
       *
       * Note that, in AngularJS, there is also a `$destroy` jQuery event, which can be used to
       * clean up DOM bindings before an element is removed from the DOM.
       */
      $destroy: function() {
        // we can't destroy the root scope or a scope that has been already destroyed
        if ($rootScope == this || this.$$destroyed) return;
        var parent = this.$parent;

        this.$broadcast('$destroy');
        this.$$destroyed = true;

        if (parent.$$childHead == this) parent.$$childHead = this.$$nextSibling;
        if (parent.$$childTail == this) parent.$$childTail = this.$$prevSibling;
        if (this.$$prevSibling) this.$$prevSibling.$$nextSibling = this.$$nextSibling;
        if (this.$$nextSibling) this.$$nextSibling.$$prevSibling = this.$$prevSibling;

        // This is bogus code that works around Chrome's GC leak
        // see: https://github.com/angular/angular.js/issues/1313#issuecomment-10378451
        this.$parent = this.$$nextSibling = this.$$prevSibling = this.$$childHead =
            this.$$childTail = null;
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$eval
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Executes the `expression` on the current scope and returns the result. Any exceptions in the
       * expression are propagated (uncaught). This is useful when evaluating Angular expressions.
       *
       * # Example
       * <pre>
           var scope = ng.$rootScope.Scope();
           scope.a = 1;
           scope.b = 2;

           expect(scope.$eval('a+b')).toEqual(3);
           expect(scope.$eval(function(scope){ return scope.a + scope.b; })).toEqual(3);
       * </pre>
       *
       * @param {(string|function())=} expression An angular expression to be executed.
       *
       *    - `string`: execute using the rules as defined in  {@link guide/expression expression}.
       *    - `function(scope)`: execute the function with the current `scope` parameter.
       *
       * @returns {*} The result of evaluating the expression.
       */
      $eval: function(expr, locals) {
        return $parse(expr)(this, locals);
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$evalAsync
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Executes the expression on the current scope at a later point in time.
       *
       * The `$evalAsync` makes no guarantees as to when the `expression` will be executed, only that:
       *
       *   - it will execute after the function that scheduled the evaluation (preferably before DOM rendering).
       *   - at least one {@link ng.$rootScope.Scope#$digest $digest cycle} will be performed after `expression` execution.
       *
       * Any exceptions from the execution of the expression are forwarded to the
       * {@link ng.$exceptionHandler $exceptionHandler} service.
       *
       * __Note:__ if this function is called outside of a `$digest` cycle, a new `$digest` cycle will be scheduled.
       * However, it is encouraged to always call code that changes the model from within an `$apply` call.
       * That includes code evaluated via `$evalAsync`.
       *
       * @param {(string|function())=} expression An angular expression to be executed.
       *
       *    - `string`: execute using the rules as defined in {@link guide/expression expression}.
       *    - `function(scope)`: execute the function with the current `scope` parameter.
       *
       */
      $evalAsync: function(expr) {
        // if we are outside of an $digest loop and this is the first time we are scheduling async task also schedule
        // async auto-flush
        if (!$rootScope.$$phase && !$rootScope.$$asyncQueue.length) {
          $browser.defer(function() {
            if ($rootScope.$$asyncQueue.length) {
              $rootScope.$digest();
            }
          });
        }

        this.$$asyncQueue.push({scope: this, expression: expr});
      },

      $$postDigest : function(fn) {
        this.$$postDigestQueue.push(fn);
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$apply
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * `$apply()` is used to execute an expression in angular from outside of the angular framework.
       * (For example from browser DOM events, setTimeout, XHR or third party libraries).
       * Because we are calling into the angular framework we need to perform proper scope life cycle
       * of {@link ng.$exceptionHandler exception handling},
       * {@link ng.$rootScope.Scope#$digest executing watches}.
       *
       * ## Life cycle
       *
       * # Pseudo-Code of `$apply()`
       * <pre>
           function $apply(expr) {
             try {
               return $eval(expr);
             } catch (e) {
               $exceptionHandler(e);
             } finally {
               $root.$digest();
             }
           }
       * </pre>
       *
       *
       * Scope's `$apply()` method transitions through the following stages:
       *
       * 1. The {@link guide/expression expression} is executed using the
       *    {@link ng.$rootScope.Scope#$eval $eval()} method.
       * 2. Any exceptions from the execution of the expression are forwarded to the
       *    {@link ng.$exceptionHandler $exceptionHandler} service.
       * 3. The {@link ng.$rootScope.Scope#$watch watch} listeners are fired immediately after the expression
       *    was executed using the {@link ng.$rootScope.Scope#$digest $digest()} method.
       *
       *
       * @param {(string|function())=} exp An angular expression to be executed.
       *
       *    - `string`: execute using the rules as defined in {@link guide/expression expression}.
       *    - `function(scope)`: execute the function with current `scope` parameter.
       *
       * @returns {*} The result of evaluating the expression.
       */
      $apply: function(expr) {
        try {
          beginPhase('$apply');
          return this.$eval(expr);
        } catch (e) {
          $exceptionHandler(e);
        } finally {
          clearPhase();
          try {
            $rootScope.$digest();
          } catch (e) {
            $exceptionHandler(e);
            throw e;
          }
        }
      },

      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$on
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Listens on events of a given type. See {@link ng.$rootScope.Scope#$emit $emit} for discussion of
       * event life cycle.
       *
       * The event listener function format is: `function(event, args...)`. The `event` object
       * passed into the listener has the following attributes:
       *
       *   - `targetScope` - `{Scope}`: the scope on which the event was `$emit`-ed or `$broadcast`-ed.
       *   - `currentScope` - `{Scope}`: the current scope which is handling the event.
       *   - `name` - `{string}`: name of the event.
       *   - `stopPropagation` - `{function=}`: calling `stopPropagation` function will cancel further event
       *     propagation (available only for events that were `$emit`-ed).
       *   - `preventDefault` - `{function}`: calling `preventDefault` sets `defaultPrevented` flag to true.
       *   - `defaultPrevented` - `{boolean}`: true if `preventDefault` was called.
       *
       * @param {string} name Event name to listen on.
       * @param {function(event, args...)} listener Function to call when the event is emitted.
       * @returns {function()} Returns a deregistration function for this listener.
       */
      $on: function(name, listener) {
        var namedListeners = this.$$listeners[name];
        if (!namedListeners) {
          this.$$listeners[name] = namedListeners = [];
        }
        namedListeners.push(listener);

        return function() {
          namedListeners[indexOf(namedListeners, listener)] = null;
        };
      },


      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$emit
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Dispatches an event `name` upwards through the scope hierarchy notifying the
       * registered {@link ng.$rootScope.Scope#$on} listeners.
       *
       * The event life cycle starts at the scope on which `$emit` was called. All
       * {@link ng.$rootScope.Scope#$on listeners} listening for `name` event on this scope get notified.
       * Afterwards, the event traverses upwards toward the root scope and calls all registered
       * listeners along the way. The event will stop propagating if one of the listeners cancels it.
       *
       * Any exception emitted from the {@link ng.$rootScope.Scope#$on listeners} will be passed
       * onto the {@link ng.$exceptionHandler $exceptionHandler} service.
       *
       * @param {string} name Event name to emit.
       * @param {...*} args Optional set of arguments which will be passed onto the event listeners.
       * @return {Object} Event object (see {@link ng.$rootScope.Scope#$on}).
       */
      $emit: function(name, args) {
        var empty = [],
            namedListeners,
            scope = this,
            stopPropagation = false,
            event = {
              name: name,
              targetScope: scope,
              stopPropagation: function() {stopPropagation = true;},
              preventDefault: function() {
                event.defaultPrevented = true;
              },
              defaultPrevented: false
            },
            listenerArgs = concat([event], arguments, 1),
            i, length;

        do {
          namedListeners = scope.$$listeners[name] || empty;
          event.currentScope = scope;
          for (i=0, length=namedListeners.length; i<length; i++) {

            // if listeners were deregistered, defragment the array
            if (!namedListeners[i]) {
              namedListeners.splice(i, 1);
              i--;
              length--;
              continue;
            }
            try {
              //allow all listeners attached to the current scope to run
              namedListeners[i].apply(null, listenerArgs);
            } catch (e) {
              $exceptionHandler(e);
            }
          }
          //if any listener on the current scope stops propagation, prevent bubbling
          if (stopPropagation) return event;
          //traverse upwards
          scope = scope.$parent;
        } while (scope);

        return event;
      },


      /**
       * @ngdoc function
       * @name ng.$rootScope.Scope#$broadcast
       * @methodOf ng.$rootScope.Scope
       * @function
       *
       * @description
       * Dispatches an event `name` downwards to all child scopes (and their children) notifying the
       * registered {@link ng.$rootScope.Scope#$on} listeners.
       *
       * The event life cycle starts at the scope on which `$broadcast` was called. All
       * {@link ng.$rootScope.Scope#$on listeners} listening for `name` event on this scope get notified.
       * Afterwards, the event propagates to all direct and indirect scopes of the current scope and
       * calls all registered listeners along the way. The event cannot be canceled.
       *
       * Any exception emitted from the {@link ng.$rootScope.Scope#$on listeners} will be passed
       * onto the {@link ng.$exceptionHandler $exceptionHandler} service.
       *
       * @param {string} name Event name to broadcast.
       * @param {...*} args Optional set of arguments which will be passed onto the event listeners.
       * @return {Object} Event object, see {@link ng.$rootScope.Scope#$on}
       */
      $broadcast: function(name, args) {
        var target = this,
            current = target,
            next = target,
            event = {
              name: name,
              targetScope: target,
              preventDefault: function() {
                event.defaultPrevented = true;
              },
              defaultPrevented: false
            },
            listenerArgs = concat([event], arguments, 1),
            listeners, i, length;

        //down while you can, then up and next sibling or up and next sibling until back at root
        do {
          current = next;
          event.currentScope = current;
          listeners = current.$$listeners[name] || [];
          for (i=0, length = listeners.length; i<length; i++) {
            // if listeners were deregistered, defragment the array
            if (!listeners[i]) {
              listeners.splice(i, 1);
              i--;
              length--;
              continue;
            }

            try {
              listeners[i].apply(null, listenerArgs);
            } catch(e) {
              $exceptionHandler(e);
            }
          }

          // Insanity Warning: scope depth-first traversal
          // yes, this code is a bit crazy, but it works and we have tests to prove it!
          // this piece should be kept in sync with the traversal in $digest
          if (!(next = (current.$$childHead || (current !== target && current.$$nextSibling)))) {
            while(current !== target && !(next = current.$$nextSibling)) {
              current = current.$parent;
            }
          }
        } while ((current = next));

        return event;
      }
    };

    var $rootScope = new Scope();

    return $rootScope;


    function beginPhase(phase) {
      if ($rootScope.$$phase) {
        throw $rootScopeMinErr('inprog', '{0} already in progress', $rootScope.$$phase);
      }

      $rootScope.$$phase = phase;
    }

    function clearPhase() {
      $rootScope.$$phase = null;
    }

    function compileToFn(exp, name) {
      var fn = $parse(exp);
      assertArgFn(fn, name);
      return fn;
    }

    /**
     * function used as an initial value for watchers.
     * because it's unique we can easily tell it apart from other values
     */
    function initWatchVal() {}
  }];
}