Redirecting to a certain route based on condition

I'm writing a small AngularJS app that has a login view and a main view, configured like so:

$routeProvider
 .when('/main' , {templateUrl: 'partials/main.html',  controller: MainController})
 .when('/login', {templateUrl: 'partials/login.html', controller: LoginController})
 .otherwise({redirectTo: '/login'});

My LoginController checks the user/pass combination and sets a property on the $rootScope reflecting this:

function LoginController($scope, $location, $rootScope) {
 $scope.attemptLogin = function() {
   if ( $scope.username == $scope.password ) { // test
        $rootScope.loggedUser = $scope.username;
        $location.path( "/main" );
    } else {
        $scope.loginError = "Invalid user/pass.";
    }
}

Everything works, but if I access http://localhost/#/main I end up bypassing the login screen. I wanted to write something like "whenever the route changes, if $rootScope.loggedUser is null then redirect to /login"

...

... wait. Can I listen to route changes somehow? I'll post this question anyway and keep looking.

After some diving through some documentation and source code, I think I got it working. Perhaps this will be useful for someone else?

I added the following to my module configuration:

angular.module(...)
 .config( ['$routeProvider', function($routeProvider) {...}] )
 .run( function($rootScope, $location) {

    // register listener to watch route changes
    $rootScope.$on( "$routeChangeStart", function(event, next, current) {
      if ( $rootScope.loggedUser == null ) {
        // no logged user, we should be going to #login
        if ( next.templateUrl != "partials/login.html" ) {
          // not going to #login, we should redirect now
          $location.path( "/login" );
        }
      }         
    });
 })

The one thing that seems odd is that I had to test the partial name (login.html) because the "next" Route object did not have a url or something else. Maybe there's a better way?

Here is maybe a more elegant and flexible solution with 'resolve' configuration property and 'promises' enabling eventual data loading on routing and routing rules depending on data.

You specify a function in 'resolve' in routing config and in the function load and check data, do all redirects. If you need to load data, you return a promise, if you need to do redirect - reject promise before that. All details can be found on $routerProvider and $q documentation pages.

'use strict';

var app = angular.module('app', [])
    .config(['$routeProvider', function($routeProvider) {
        $routeProvider
            .when('/', {
                templateUrl: "login.html",
                controller: LoginController
            })
            .when('/private', {
                templateUrl: "private.html",
                controller: PrivateController,
                resolve: {
                    factory: checkRouting
                }
            })
            .when('/private/anotherpage', {
                templateUrl:"another-private.html",
                controller: AnotherPriveController,
                resolve: {
                    factory: checkRouting
                }
            })
            .otherwise({ redirectTo: '/' });
    }]);

var checkRouting= function ($q, $rootScope, $location) {
    if ($rootScope.userProfile) {
        return true;
    } else {
        var deferred = $q.defer();
        $http.post("/loadUserProfile", { userToken: "blah" })
            .success(function (response) {
                $rootScope.userProfile = response.userProfile;
                deferred.resolve(true);
            })
            .error(function () {
                deferred.reject();
                $location.path("/");
             });
        return deferred.promise;
    }
};

For russian-speaking folks there is a post on habr "Вариант условного раутинга в AngularJS."