Angular resize directive

I have created this directive in Angular. The idea is to calculate width of height and height of specific element via style function attached to ng-style on the same element.

The directive uses underscore for debounce, and $routeScope to receive called from the element, $window to get full height and width of it.

How can I improve this code to make it more testable, more readable?

(function (ng, _) {
ng.module('mixbank.app').directive('tableResize', [
    '$window',
    '$rootScope',
    function ($window, $rootScope) {
        return function (scope, element, attrs) {
            var w = ng.element($window);
            var topOffsetCalculate = function () {
                return {
                    total: ng.element("nav.navbar-fixed-top").height() +
                    ng.element("nav.navbar-business").height() +
                    ng.element(".table-business-rules thead").height()
                }
            };
            var topOffset = topOffsetCalculate().total;
            var leftOffset = ng.element(".left-business-rules-view").outerWidth();
            var rowHeight = 58;
            var expandedRowHeight = 175;

            scope.getWindowDimensions = function () {
                return {
                    'h': w.height(),
                    'w': w.width(),
                    'th': attrs.totalRows * rowHeight + topOffset
                };
            };

            function doLayout(expandedRule) {
                var newValue = scope.getWindowDimensions();
                var possibleHeight = expandedRule ? newValue.th + expandedRowHeight : newValue.th;
                scope.style = function () {
                    var h = Math.min(possibleHeight, newValue.h);
                    return {
                        height: (h - topOffset) + 'px',
                        width: (newValue.w - leftOffset) + 'px'
                    }
                };
            }


            var resizeHandler = _.debounce(function () {
                doLayout();
                scope.$apply();
            }, 300);

            $rootScope.$on('expandRow', function (event, data) {
                typeof data != 'undefined' ? doLayout(true) : doLayout();
            });

            scope.$watch(function () {
                return attrs.totalRows;
            }, function () {
                doLayout();
            });

            scope.$on('$destroy', function () {
                w.off('resize', resizeHandler);
            });
            w.on('resize', resizeHandler);
        }
    }
])
;}(window.angular, _));