scalyr.js

/**
 * @license scalyr v1.0
 * (c) 2013 Scalyr, Inc. http://scalyr.com
 * License: MIT
 */
// You may just depend on the 'sly' module to pull in all of the
// dependencies.
angular.module('sly', ['slyEvaluate', 'slyRepeat']);
/**
 * @fileoverview 
 * Defines core functions used throughout the Scalyr javascript
 * code base.  This file is included on every page.
 *
 * @author Steven Czerwinski <czerwin@scalyr.com>
 */

/**
 * @param {Object} value The value to check
 * @returns {Boolean} True if value is an Array
 */
function isArray(value) {
  return Object.prototype.toString.call(value) === '[object Array]';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is a Boolean
 */
function isBoolean(value) {
  return typeof value == 'boolean';
}

/**
 * @param {Object} value The value to check
 * @returns {Boolean} True if value is a Date object
 */
function isDate(value) {
  return Object.prototype.toString.call(value) === '[object Date]';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is undefined
 */
function isDefined(value) {
  return typeof value != 'undefined';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is a Function
 */
function isFunction(value) {
  return typeof value == 'function';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is null
 */
function isNull(value) {
  return value === null;
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is a Number
 */
function isNumber(value) {
  return typeof value == 'number'; 
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is an Object, not including null
 */
function isObject(value) {
  return value !== null && typeof value == 'object';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is a string
 */
function isString(value) {
  return typeof value == 'string';
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} True if value is undefined
 */
function isUndefined(value) {
  return typeof value == 'undefined';
}

/**
 * Converts a String or Boolean value to a Boolean.
 *
 * @param {String|Boolean} value The value to convert
 * @returns {Boolean} Returns true for any String that is not
 *   null, empty String, or 'false'.  If value is a Boolean,
 *   returns value
 */
function convertToBoolean(value) {
  if (isBoolean(value))
    return value;
  return value !== null && value !== '' && value !== 'false';
}

/**
 * Determines if obj has a property named prop.
 *
 * @param {Object} obj The object to check
 * @returns {Boolean} Returns true if obj has a property named
 *   prop.  Only considers the object's own properties
 */
function hasProperty(obj, prop) {
  return obj.hasOwnProperty(prop);
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} Returns true if value is a String
 *   and has zero length, or if null or undefined
 */
function isStringEmpty(value) {
  return isNull(value) || isUndefined(value) ||
    (isString(value) && (value.length == 0));
}

/**
 * @param {*} value The value to check
 * @returns {Boolean} Returns true if value is a String
 *   and has non-zero length
 */
function isStringNonempty(value) {
  return isString(value) && (value.length > 0);
}

/**
 * Returns input with the first letter capitalized.
 * The input may not be zero length.
 *
 * @param {String} input The String to capitalize.
 * @returns {String} Returns input with the first letter
 *   capitalized.
 */
function upperCaseFirstLetter(input) {
  return input.charAt(0).toUpperCase() + input.slice(1);
}

/**
 * Returns true if obj1 and obj2 are equal.  This should
 * only be used for Arrays, Objects, and value types.  This is a deep
 * comparison, comparing each property and recursive property to
 * be equal (not just ===).
 *
 * Two Objects or values are considered equivalent if at least one of the following is true:
 *  - Both objects or values pass `===` comparison.
 *  - Both objects or values are of the same type and all of their properties pass areEqual
 *    comparison.
 *  - Both values are NaN. (In JavasScript, NaN == NaN => false. But we consider two NaN as equal).
 *
 * Note, during property comparision, properties with function values are ignores as are property
 * names beginning with '$'.
 *
 * See angular.equal for more details.
 *
 * @param {Object|Array|value} obj1 The first object
 * @param {Object|Array|value} obj2 The second object
 * @returns {Boolean} True if the two objects are equal using a deep
 *   comparison. 
 */
function areEqual(obj1, obj2) {
  return angular.equals(obj1, obj2);
}

/**
 * @param {Number} a The first Number
 * @param {Number} b The second Number
 * @returns {Number} The minimum of a and b
 */
function min(a, b) {
  return a < b ? a : b;
}

/**
 * @param {Number} a The first Number
 * @param {Number} b The second Number
 * @returns {Number} The maximum of a and b
 */
function max(a, b) {
  return a > b ? a : b;
}

/**
 * Returns true if the specified String begins with prefix.
 *
 * @param {*} input The input to check
 @ @param {String} prefix The prefix
 * @returns {Boolean} True if input is a string that begins with prefix
 */
function beginsWith(input, prefix) {
  return isString(input) && input.lastIndexOf(prefix, 0) == 0;
}

/**
 * Returns true if the specified String ends with prefix.
 *
 * @param {*} input The input to check
 @ @param {String} postfix The postfix
 * @returns {Boolean} True if input is a string that ends with postfix
 */
function endsWith(input, postfix) {
  return isString(input) && input.indexOf(postfix, input.length - postfix.length) !== -1;
}

/**
 * Returns a deep copy of source, where source can be an Object or an Array.  If a destination is
 * provided, all of its elements (for Array) or properties (for Objects) are deleted and then all
 * elements/properties from the source are copied to it.   If source is not an Object or Array, 
 * source is returned.
 *
 * See angular.copy for more details.
 * @param {Object|Array} source The source
 * @param {Object|Array} destination Optional object to copy the elements to
 * @returns {Object|Array} The deep copy of source
 */
function copy(source, destination) {
  return angular.copy(source, destination);
}

/**
 * Removes property from obj.
 *
 * @param {Object} obj The object
 * @param {String} property The property name to delete
 */
function removeProperty(obj, property) {
  delete obj[property];
}

/**
 * Removes all properties in the array from obj.
 *
 * @param {Object} obj The object
 * @param {Array} properties The properties to remove
 */
function removeProperties(obj, properties) {
  for (var i = 0; i < properties.length; ++i)
    delete obj[properties[i]];
}

/**
 * Invokes the iterator function once for each item in obj collection, which can be either
 * an Object or an Array. The iterator function is invoked with iterator(value, key),
 * where value is the value of an object property or an array element and key is the
 * object property key or array element index. Specifying a context for the function is
 * optional.  If specified, it becomes 'this' when iterator function is invoked.
 *
 * See angular.forEach for more details.
 *
 * @param {Object|Array} The Object or Array over which to iterate
 * @param {Function} iterator The iterator function to invoke
 * @param {Object} context The value to set for 'this' when invoking the
 *   iterator function. This is optional
 */
function forEach(obj, iterator, context) {
  return angular.forEach(obj, iterator, context);
}

/**
 * Used to define a Scalyr javascript library and optionally declare
 * dependencies on other libraries.  All javascript code not defined in
 * this file should be defined as part of a library.
 *
 * The first argument is the name to call the library.  The second argument
 * is either a Constructor object for the library or an array where the last
 * element is the Constructor for the library and the first to N-1 are string
 * names of the libraries this one depends on.  If you do declare dependencies,
 * the libraries are passed in the Constructor create method in the same order
 * as the strings are defined.
 *
 * Example:
 *  defineScalyrJsLibrary('myUtils', function() {
 *    var fooFunction = function(a, b) {
 *        return a + b;
 *    };
 *    return {
 *      foo: fooFunction
 *    };
 *  });
 *
 *  defineScalyrJsLibrary('anotherUtils', [ 'myUtils', function(myUtils) {
 *    var barFunction = function(a, b) {
 *      return myUtils.foo(a, b);
 *    };
 *    return {
 *      bar: barFunction
 *    };
 *  });
 *
 * @param {String} libraryName The name for the library
 * @param {Constructor|Array} libraryExporter The exporter for the
 *   library.  See above for details
 */
function defineScalyrJsLibrary(libraryName, libraryExporter) {
  var moduleDependencies = [];
  if (libraryExporter instanceof Array) {
    for (var i = 0; i < libraryExporter.length - 1; ++i)
      moduleDependencies.push(libraryExporter[i]);
  }
  
  return angular.module(libraryName, moduleDependencies)
    .factory(libraryName, libraryExporter);              
}

/**
 * Similar to defineScalyrJsLibary but instead of declaring
 * a purely javascript library, this declares an Angular module
 * library.  The moduleName should be a string used to identify
 * this module.  The dependencies is an array with the string
 * names of Angular modules, Scalyr Angular modules, or Scalyr
 * javascript libraries to depend on.  The returned object
 * can be used to define directives, etc similar to angular.module.
 *
 * Example:
 *  defineScalyrAngularModule('slyMyModule', [ 'myTextUtils'])
 *  .filter('camelCase', function(myTextUtils) {
 *     return function(input) {
 *       return myTextUtils.camelCase(input);
 *     };
 *  });
 *
 * @param {String} moduleName The name of the module
 * @param {Array} dependencies The names of modules to depend on
 */
function defineScalyrAngularModule(moduleName, dependencies) {
  return angular.module(moduleName, dependencies);
}
/**
 * @fileoverview
 * Module: slyEvaluate
 *
 * Defines several directives related to preventing evaluating watchers
 * on scopes under certain conditions.  Here's a list of the directives
 * and brief descriptions.  See down below for more details.
 *
 *  slyEvaluateOnlyWhen:  A directive that prevents updating / evaluating
 *      all bindings for the current element and its children unless
 *      the expression has changed values.  It currently assumes the
 *      expression evaluates to an object and detects changes only by
 *      a change in object reference.
 *
 *  slyAlwaysEvaluate: Can only be used in conjunction with the
 *      slyEvaluateOnlyWhen directive.  This directive will ensure that
 *      any expression that is being watched will always be evaluated
 *      if it contains the specified string (i.e., it will ignore whether
 *      or not the slyEvaluateOnlyWhen expression has changed.)  This
 *      is useful when you wish to check some expressions all the time.
 *
 *  slyPreventEvaluationWhenHidden:  Will only evaluate the bindings
 *      for the current element and its children if the current element
 *      is not hidden (detected by the element having the ng-hide CSS class.)
 *
 *  slyShow:  Will hide the element if the expression evaluates to false.
 *      Uses ng-hide to hide the element.  This is almost exactly the same
 *      as ngShow, but it has the advantage that it works better with
 *      slyPreventEvaluationWhenHidden by guaranteeing it will always evaluate
 *      its show expression to determine if it should or should not be hidden.
 */
defineScalyrAngularModule('slyEvaluate', ['gatedScope'])
/**
 * Directive for preventing all bound expressions in the current element and its children
 * from being evaluated unless the specified expression evaluates to a different object.
 * Currently, the value assigned to the 'slyEvaluateOnlyWhen' must evaluate to an object.
 * Also, reference equality is used to determine if the expression has changed.
 * TODO: Make this more versatile, similar to $watch.  For now, this is all we need.
 */
.directive('slyEvaluateOnlyWhen', ['$parse', function ($parse) {
  return {
    // We create a new scope just because it helps segment the gated watchers
    // from the parent scope.  Unclear if this is that important for perf.
    scope: true,
    restrict: 'A',
    compile: function compile(tElement, tAttrs) {       
      return {
        // We need a separate pre-link function because we want to modify the scope before any of the
        // children are passed it.
        pre: function preLink(scope, element, attrs) {
          var previousValue = null;
          var initialized = false;

          var expressionToCheck = $parse(attrs['slyEvaluateOnlyWhen']);
          var alwaysEvaluateString = null;
          if (hasProperty(attrs, 'slyAlwaysEvaluate')) {
            alwaysEvaluateString = attrs['slyAlwaysEvaluate'];
            if (isStringEmpty(alwaysEvaluateString))
              throw new Exception('Empty string is illegal for value of slyAlwaysEvaluate');
          }
          scope.$addWatcherGate(function evaluteOnlyWhenChecker() {
            // We should only return true if expressionToCheck evaluates to a value different
            // than previousValue.
            var currentValue = expressionToCheck(scope);
            if (!initialized) {
              initialized = true;
              previousValue = currentValue;
              return true;
            }
            var result = previousValue !== currentValue;
            previousValue = currentValue;
            return result;
          }, function shouldGateWatcher(watchExpression) {
            // Should return true if the given watcher that's about to be registered should
            // be gated.
            return isNull(alwaysEvaluateString) || 
                   !(isStringNonempty(watchExpression) && (watchExpression.indexOf(alwaysEvaluateString) >= 0));
          });
        },
      };
    },
  };
}])
/**
 * Directive for overriding the 'slyEvaluateOnlyWhen' expression for the current element.
 * This directive takes a single string value.  If this string value is found anywhere in
 * an expression that normally would not be evaluated due to the 'slyEvaluateOnlyWhen'
 * directive, it is evaluated, regardless of whether or not the value for the expression in
 * 'slyEvaluateOnlyWhen' has changed.  This is very useful when a certain expression used by
 * one of the children of the current element should always be evaluated and is not affected
 * by the expression specified in slyEvaluateOnlyWhen.
 */
.directive('slyAlwaysEvaluate', function() {
  // This is just a place holder to show that slyAlwaysEvaluate is a legal
  // directive.  The real work for this directive is done in slyEvaluateOnlyWhen.
  return {
    restrict: 'A',
    link: function(scope, element, attrs) {
    },
  };
})
/**
 * Directive for showing an element, very similar to ngShow.  However, this directive
 * works better with slyPreventEvaluationWhenHidden because it is ensure it always
 * will evaluate the show expression to determine if it should be shown or hidden
 * even if slyPreventEvaluationWhenHidden is in effect.  This directive also uses
 * the ng-hide css class to actually hide the element.
 *
 * NOTE: We might be able to get better performance if we have this directive directly
 * perform a callback on slyPreventEvaluationWhenHidden when it is shown/hidden rather
 * than having that directive register a watcher on the css class.
 */
.directive('slyShow', ['$animate', function($animate) {
  /**
   * @param {*} value The input
   * @return {Boolean} True if the value is truthy as determined by angular rules.
   *
   * Note:  This is copied from the Angular source because it is not exposed by Angular
   * but we want our directive to behave the same as ngShow.  Think about moving this
   * to core.js.
   */
  function toBoolean(value) {
    if (value && value.length !== 0) {
      var v = ("" + value);
      v = isString(v) ? v.toLowerCase() : v;
      value = !(v == 'f' || v == '0' || v == 'false' || v == 'no' || v == 'n' || v == '[]');
    } else {
      value = false;
    }
    return value;
  }

  return {
    restrict: 'A',
    link: function slyShowLink(scope, element, attr) {
      scope.$watch(attr.slyShow, function ngSlyShowAction(value){
        $animate[toBoolean(value) ? 'removeClass' : 'addClass'](element, 'ng-hide');
      }, false, 'slyShow'); },
  };
}])
/**
 * Directive for preventing all bound expressions in the current element and its children
 * from being evaluated if the current element is hidden as determined by whether or not
 * it has the ng-hide class.
 */
.directive('slyPreventEvaluationWhenHidden', function () {
  return {
    restrict: 'A',
    // We create a new scope just because it helps segment the gated watchers
    // from the parent scope.  Unclear if this is that important for perf.
    scope: true,
    compile: function compile(tElement, tAttrs) {       
      return {
        // We need a separate pre-link function because we want to modify the scope before any of the
        // children are passed it.
        pre: function preLink(scope, element, attrs) {
          scope.$addWatcherGate(function hiddenChecker() {
            // Should only return true if the element is not hidden.
            return !element.hasClass('ng-hide');
          }, function hiddenDecider(watchExpression, listener, equality, directiveName) {
            // Make an exception for slyShow.. do not gate its watcher.
            if (isDefined(directiveName) && (directiveName == 'slyShow'))
              return false;
            return true;
          });
        },
      };
    },
  };
});

/**
 * @fileoverview
 * Module:  slyRepeat
 *
 * Contains the slyRepeat directive, which is is a modified version of the
 * ngRepeat directive that is meant to be more efficient for creating and
 * recreating large lists of bound elements.  In particular, it has an
 * optimization that will prevent DOM elements from being constantly created
 * and destroyed as the contents of the repeated elements change.  It does this
 * by not destroying DOM elements when they are no longer needed, but instead,
 * just hiding them. This might not work for all use cases, but for it does
 * for the ones we do wish to heavily optimize.  For eample, through profiling,
 * we found that destroying DOM elements when flipping through log view pages
 * represented a large chunk of CPU time.
 *
 * Cavaets:  The collection expression must evaluate to an array.  Animators
 *   will not work.  Track By does not work.  Use at your own peril.
 *
 * @author Steven Czerwinski <czerwin@scalyr.com>
 */
defineScalyrAngularModule('slyRepeat', ['gatedScope'])
.directive('slyRepeat', ['$animate', '$parse', function ($animate, $parse) {
  
  /**
   * Sets the scope contained in elementScope to gate all its
   * watchers based on the isActiveForRepeat proprety.
   *
   * @param {Object} elementScope The object containing the
   *   scope and isActiveForRepeat properties.
   */
  function gateWatchersForScope(elementScope) {
    elementScope.scope.$addWatcherGate(function() {
      return elementScope.isActiveForRepeat;
    });
  }

  return {
    restrict: 'A',
    scope: true,
    transclude: 'element',
    priority: 1000,
    terminal: true,
    compile: function(element, attr, linker) {
      // Most of the work is done in the post-link function.
      return function($scope, $element, $attr) {
        // This code is largely based on ngRepeat.

        // Parse the expression.  It should look like:
        // x in some-expression
        var expression = $attr.slyRepeat;
        var match = expression.match(/^\s*(.+)\s+in\s+(.*?)$/);
        if (!match) {
          throw Error("Expected slyRepeat in form of '_item_ in _collection_' but got '" +
              expression + "'.");
        }

        var iterVar = match[1];
        var collectionExpr = match[2];

        match = iterVar.match(/^(?:([\$\w]+))$/);
        if (!match) {
          throw Error("'item' in 'item in collection' should be identifier but got '" +
              lhs + "'.");
        }
        
        // previousElements will store references to the already existing (DOM) elements
        // that were last used for the last rendering of this repeat and were visible.
        // We will re-use these elements when executing the next rendering of the repeat when
        // the iteration value changes.
        var previousElements = [];
        // previousElementsBuffer will store references to the already existing (DOM) elements
        // that are in the page but were not used for the last rendering of this repeat and were
        // therefore marked as inactive and not visible.  This happens if the length of the repeat
        // iteration goes down over time, since we do not remove the elements.  If the repeat length
        // was first 10, then 5, we will end up with the last 5 elements in the previousElementBuffer.
        // We keep this in case the length increases again.
        var previousElementBuffer = [];
        
        var deregisterCallback = $scope.$watchCollection(collectionExpr, function(collection) {         
          if (!isArray(collection))
            throw Error("'collection' did not evaluate to an array.  expression was " + collectionExpr);
          var originalPreviousElementsLength = previousElements.length;
          // First, reconcile previousElements and collection with respect to the previousElementBuffer.
          // Basically, try to grow previousElements to collection.length if we can.
          if ((previousElements.length < collection.length) && (previousElementBuffer.length > 0)) {
            var limit = previousElements.length + previousElementBuffer.length;
            if (limit > collection.length)
              limit = collection.length;       
            previousElements = previousElements.concat(previousElementBuffer.splice(0, limit - previousElements.length));
          }
          
          var currentElements = null;
          var currentElementBuffer = [];

          var newElements = [];
          if (collection.length > previousElements.length) {
            // Add in enough elements to account for the larger collection.
            for (var i = previousElements.length; i < collection.length; ++i) {
              // Need to add in an element for each new item in the collection.
              var newElement = {
                  scope: $scope.$new(),
                  isActiveForRepeat: true,
              };
              
              gateWatchersForScope(newElement);
              newElement.scope.$index = i;
              newElement.scope.$first = (i == 0);
              newElements.push(newElement);
            }
            currentElements = previousElements.concat(newElements);
            currentElementBuffer = previousElementBuffer;
          } else if (collection.length < previousElements.length) {
            for (var i = collection.length; i < previousElements.length; ++i)
              previousElements[i].isActiveForRepeat = false;

            currentElementBuffer = previousElements.splice(collection.length, previousElements.length - collection.length).concat(
                previousElementBuffer);
            currentElements = previousElements;
          } else {
            currentElements = previousElements;
            currentElementBuffer = previousElementBuffer;
          }
          
          // We have to fix up the last and middle values in the scope for each element in
          // currentElements, since their roles may have changed with the new length.
          // We always have to fix the last element.
          if (currentElements.length > 0) {
            var firstIndexToFix = currentElements.length - 1;
            var lastIndexToFix = currentElements.length - 1;
            // We also have to fix any new elements that were added.
            if (originalPreviousElementsLength < currentElements.length) {
              firstIndexToFix = originalPreviousElementsLength;
            }
            // And we usually have to fix the element before the first element we modified
            // in case it used to be last.
            if (firstIndexToFix > 0) {
              firstIndexToFix = firstIndexToFix - 1;
            }
            for (var i = firstIndexToFix; i <= lastIndexToFix; ++i) {
              currentElements[i].scope.$last = (i == (currentElements.length - 1));
              currentElements[i].scope.$middle = ((i != 0) && (i != (currentElements.length - 1)));
              if (!currentElements[i].isActiveForRepeat) {
                // If it is not marked as active, make it active.  This is also indicates that
                // the element is currently hidden, so we have to unhide it.
                currentElements[i].isActiveForRepeat = true; 
                currentElements[i].element.css('display', '');
              }
            }
          }
          
          // Hide all elements that have recently become inactive.
          for (var i = 0; i < currentElementBuffer.length; ++i) {
            if (currentElementBuffer[i].isActiveForRepeat)
              break;
            currentElementBuffer[i].element.css('display', 'none');
          }

          // Assign the new value for the iter variable for each scope.
          for (var i = 0; i < currentElements.length; ++i) {
            currentElements[i].scope[iterVar] = collection[i];
          }

          // We have to go back now and clone the DOM element for any new elements we
          // added and link them in.  We clone the last DOM element we had created already
          // for this Repeat.
          var prevElement = $element;
          if (previousElements.length > 0)
            prevElement = previousElements[previousElements.length - 1].element;
          for (var i = 0; i < newElements.length; ++i) {
            linker(newElements[i].scope, function(clone) {
              $animate.enter(clone, null, prevElement);
              prevElement = clone;
              newElements[i].element = clone;
            });
          }
            
          previousElements = currentElements;
          previousElementBuffer = currentElementBuffer;
        });
        $scope.$on('$destroy', function() {
          deregisterCallback();
        });
      };
    }
  };
}]);
/**
 * @fileoverview
 * Defines an extension to angular.Scope that allows for registering
 * 'gating functions' on a scope that will prevent all future watchers
 * registered on the scope from being evaluated unless the gating function
 * returns true.
 *
 * By depending on this module, the $rootScope instance and angular.Scope
 * class are automatically extended to implement this new capability.
 *
 * Warning, this implementation depends on protected/private variables
 * in the angular.Scope implementation and therefore can break in the
 * future due to changes in the angular.Scope implementation.  Use at
 * your own risk.
 */
defineScalyrAngularModule('gatedScope', [])
.config(['$provide', function($provide) {
  // We use a decorator to override methods in $rootScope.
  $provide.decorator('$rootScope', ['$delegate', '$exceptionHandler', 
      function ($rootScope, $exceptionHandler) {

    // Make a copy of $rootScope's original methods so that we can access
    // them to invoke super methods in the ones we override.
    scopePrototype = {};
    for (var key in $rootScope) {
      if (isFunction($rootScope[key]))
        scopePrototype[key] = $rootScope[key];
    }

    var Scope = $rootScope.constructor;

    // Hold all of our new methods.
    var methodsToAdd = {
    };

    // A constant value that the $digest loop implementation depends on.  We
    // grab it down below.
    var initWatchVal;

    /**
     * @param {Boolean} isolate Whether or not the new scope should be isolated.
     * @returns {Scope} A new child scope
     */
    methodsToAdd.$new = function(isolate) {
      // Because of how scope.$new works, the returned result
      // should already have our new methods.
      var result = scopePrototype.$new.call(this, isolate);
      
      // We just have to do the work that normally a child class's
      // constructor would perform -- initializing our instance vars.
      result.$$gatingFunction = this.$$gatingFunction;
      result.$$shouldGateFunction = this.$$shouldGateFunction;
      result.$$gatedWatchers = [];

      return result;
    };

    /**
     * Digests all of the gated watchers for the specified gating function.
     *
     * @param {Function} targetGatingFunction The gating function associated
     *   with the watchers that should be digested
     * @returns {Boolean} True if any of the watchers were dirty
     */
    methodsToAdd.$digestGated = function gatedScopeDigest(targetGatingFunction) {
      // Note, most of this code was stolen from angular's Scope.$digest method.
      var watch, value,
        watchers,
        length,
        next, current = this, target = this,
        dirty = false;

      do { // "traverse the scopes" loop
        if (watchers = current.$$gatedWatchers) {
          // process our watches
          length = watchers.length;
          while (length--) {
            try {
              watch = watchers[length];
              // Scalyr edit: We do not process a watch function if it is does not
              // have the same gating function for which $digestGated was invoked.
              if (watch.gatingFunction !== targetGatingFunction)
                continue;

              // 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);
                // Scalyr edit:  Removed the logging code for when the ttl is reached
                // here because we don't have access to the ttl in this method.
              }
            } 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!
        // Scalyr edit: This insanity warning was from angular.  We only modified this
        // code by checking the $$gatingFunction because it's a good optimization to only go
        // down a child of a parent that has the same gating function as what we are processing
        // (since if a parent already has a different gating function, there's no way any
        // of its children will have the right one).
        if (!(next = ((current.$$gatingFunction === targetGatingFunction && current.$$childHead)
              || (current !== target && current.$$nextSibling)))) {
          while(current !== target && !(next = current.$$nextSibling)) {
            current = current.$parent;
          }
        }
      } while ((current = next));

      return dirty;
    };

    /**
     * @inherited $watch
     * @param directiveName The fourth parameter is a new optional parameter that allows
     *   directives aware of this abstraction to pass in their own names to identify
     *   which directive is registering the watch.  This is then passed to the
     *   shouldGateFunction to help determine if the watcher should be gated by the current
     *   gatingFunction.
     */
    methodsToAdd.$watch = function gatedWatch(watchExpression, listener, objectEquality,
        directiveName) {
      // Determine if we should gate this watcher.
      if (!isNull(this.$$gatingFunction) && (isNull(this.$$shouldGateFunction) ||
          this.$$shouldGateFunction(watchExpression, listener, objectEquality, directiveName)))  {
        // We do a hack here to just switch out the watchers array with our own
        // gated list and then invoke the original watch function.
        var tmp = this.$$watchers;
        this.$$watchers = this.$$gatedWatchers;
        // Invoke original watch function.
        var result = scopePrototype.$watch.call(this, watchExpression, listener, objectEquality);
        this.$$watchers = tmp;
        this.$$gatedWatchers[0].gatingFunction = this.$$gatingFunction;

        // We know that the last field of the watcher object will be set to initWatchVal, so we
        // grab it here.
        initWatchVal = this.$$gatedWatchers[0].last;

        return result;
      } else {
        return scopePrototype.$watch.call(this, watchExpression, listener, objectEquality);
      }
    };
    
    /**
     * Modifies this scope so that all future watchers registered by $watch will
     * only be evaluated if gatingFunction returns true.  Optionally, you may specify
     * a function that will be evaluted on every new call to $watch with the arguments
     * passed to it, and that watcher will only be gated if the function returns true.
     *
     * @param {Function} gatingFunction The gating function which controls whether or not all future
     *   watchers registered on this scope and its children will be evaluated on a given
     *   digest cycle.  The function will be invoked (with no arguments) on every digest
     *   and if it returns a truthy result, will cause all gated watchers to be evaluated.
     * @param {Function} shouldGateFunction The function that controls whether or not
     *   a new watcher will be gated using gatingFunction.  It is evaluated with the
     *   arguments to $watch and should return true if the watcher created by those
     *   arguments should be gated
     */
    methodsToAdd.$addWatcherGate = function(gatingFunction, shouldGateFunction) {
      var changeCount = 0;
      var self = this;

      // Set a watcher that sees if our gating function is true, and if so, digests
      // all of our associated watchers.  Note, this.$watch could already have a
      // gating function associated with it, which means this watch won't be executed
      // unless all gating functions before us have evaluated to true.  We take special
      // care of this nested case below.

      // We handle nested gating function in a special way.  If we are a nested gating
      // function (meaning there is already one or more gating functions on this scope and
      // our parent scopes), then if those parent gating functions every all evaluate to
      // true (which we can tell if the watcher we register here is evaluated), then
      // we always evaluate our watcher until our gating function returns true.
      var hasNestedGates = !isNull(this.$$gatingFunction);
      var promotedWatcher = null;

      this.$watch(function() {
        if (gatingFunction()) {
          if (self.$digestGated(gatingFunction))
            ++changeCount;
        } else if (hasNestedGates && isNull(promotedWatcher)) {
          promotedWatcher = scopePrototype.$watch.call(self, function() {
            if (gatingFunction()) {
              promotedWatcher();
              promotedWatcher = null;
              if (self.$digestGated(gatingFunction))
                ++changeCount;
            }
            return changeCount;
          });
        }
        return changeCount;
      });


      if (isUndefined(shouldGateFunction))
        shouldGateFunction = null;
      this.$$gatingFunction = gatingFunction;
      this.$$shouldGateFunction = shouldGateFunction;
    };

    // Extend the original Scope object so that when
    // new instances are created, it has the new methods.
    angular.extend(Scope.prototype, methodsToAdd);

    // Also extend the $rootScope instance since it was created
    // before we got a chance to extend Scope.prototype.
    angular.extend($rootScope, methodsToAdd);

    $rootScope.$$gatingFunction = null;
    $rootScope.$$shouldGateFunction = null;
    $rootScope.$$gatedWatchers = [];

    return $rootScope;
  }]);
}]);