AngularJS でビュー固有のスタイルシートを動的に管理する方法

app.directive('head', ['$rootScope', '$compile', function($rootScope, $compile){
  return {
    restrict: 'E',
    link: function(scope, elem){
      var html = '<link rel="stylesheet" ng-repeat="(routeCtrl, cssUrl) in routeStyles" ng-href="{{cssUrl}}" />';
      elem.append($compile(html)(scope));
      scope.routeStyles = {};
      $rootScope.$on('$routeChangeStart', function (e, next, current) {
        if(current && current.$$route && current.$$route.css){
          if(!angular.isArray(current.$$route.css)){
            current.$$route.css = [current.$$route.css];
          }
          angular.forEach(current.$$route.css, function(sheet){
            delete scope.routeStyles[sheet];
          });
        }
        if(next && next.$$route && next.$$route.css){
          if(!angular.isArray(next.$$route.css)){
            next.$$route.css = [next.$$route.css];
          }
          angular.forEach(next.$$route.css, function(sheet){
            scope.routeStyles[sheet] = sheet;
          });
        }
      });
    }
  };
}]);

app.config(['$routeProvider', function($routeProvider){
  $routeProvider
    .when('/some/route/1', {
      templateUrl: 'partials/partial1.html', 
      controller: 'Partial1Ctrl',
      css: 'css/partial1.css'
    })
    .when('/some/route/2', {
      templateUrl: 'partials/partial2.html',
      controller: 'Partial2Ctrl'
    })
    .when('/some/route/3', {
      templateUrl: 'partials/partial3.html',
      controller: 'Partial3Ctrl',
      css: ['css/partial3_1.css','css/partial3_2.css']
    })
}]);