def change_enrollment(request):
    """
    This change_enrollment overloads default one. When 'enroll' action is
    specified it tries to lookup in configuration whether some url for the 
    enrolling course is set. If it is so, client is redirected to this url, 
    otherwise standard action is executed and nothing changes.
    """
    # Execute original handler
    response = student_views.change_enrollment(request)
    
    action = request.POST.get("enrollment_action")
    course_id = request.POST.get("course_id")
    callback_url = None

    # Try to lookup redirect url for course if we are enrolling
    if action is not None and action == 'enroll':
        if course_id is not None:
            try:
                callback_url = settings.ENROLL_URL_CALLBACK[course_id]
            except:
                log.debug('No url for course {0} is specified in cofiguration.'.format(course_id))
         
    # If url IS specified -- redirect there
    if callback_url is not None:
      return HttpResponse(callback_url)
    
    # Return original response
    return response

    def test_enrollment_limit_by_domain(self):
        """
            Tests that the enrollmentDomain setting is properly limiting enrollment to those who have
            the proper external auth
        """

        # create 2 course, one with limited enrollment one without
        shib_course = CourseFactory.create(org='Stanford', number='123', display_name='Shib Only')
        shib_course.enrollment_domain = 'shib:https://idp.stanford.edu/'
        self.store.update_item(shib_course, '**replace_user**')

        open_enroll_course = CourseFactory.create(org='MITx', number='999', display_name='Robot Super Course')
        open_enroll_course.enrollment_domain = ''
        self.store.update_item(open_enroll_course, '**replace_user**')

        # create 3 kinds of students, external_auth matching shib_course, external_auth not matching, no external auth
        shib_student = UserFactory.create()
        shib_student.save()
        extauth = ExternalAuthMap(external_id='[email protected]',
                                  external_email='',
                                  external_domain='shib:https://idp.stanford.edu/',
                                  external_credentials="",
                                  user=shib_student)
        extauth.save()

        other_ext_student = UserFactory.create()
        other_ext_student.username = "teststudent2"
        other_ext_student.email = "[email protected]"
        other_ext_student.save()
        extauth = ExternalAuthMap(external_id='[email protected]',
                                  external_email='',
                                  external_domain='shib:https://other.edu/',
                                  external_credentials="",
                                  user=other_ext_student)
        extauth.save()

        int_student = UserFactory.create()
        int_student.username = "teststudent3"
        int_student.email = "[email protected]"
        int_student.save()

        # Tests the two case for courses, limited and not
        for course in [shib_course, open_enroll_course]:
            for student in [shib_student, other_ext_student, int_student]:
                request = self.request_factory.post('/change_enrollment')
                request.POST.update({'enrollment_action': 'enroll',
                                     'course_id': course.id.to_deprecated_string()})
                request.user = student
                response = change_enrollment(request)
                # If course is not limited or student has correct shib extauth then enrollment should be allowed
                if course is open_enroll_course or student is shib_student:
                    self.assertEqual(response.status_code, 200)
                    self.assertTrue(CourseEnrollment.is_enrolled(student, course.id))
                    # Clean up
                    CourseEnrollment.unenroll(student, course.id)
                else:
                    self.assertEqual(response.status_code, 400)
                    self.assertFalse(CourseEnrollment.is_enrolled(student, course.id))

 def test_change_enrollment_add_to_cart(self):
     request = self.req_factory.post(reverse('change_enrollment'), {'course_id': self.course.id,
                                                                    'enrollment_action': 'add_to_cart'})
     request.user = self.user
     response = change_enrollment(request)
     self.assertEqual(response.status_code, 200)
     self.assertEqual(response.content, reverse('shoppingcart.views.show_cart'))
     self.assertTrue(shoppingcart.models.PaidCourseRegistration.contained_in_order(
         shoppingcart.models.Order.get_cart_for_user(self.user), self.course.id))

 def test_change_enrollment_add_to_cart(self):
     request = self.req_factory.post(
         reverse("change_enrollment"),
         {"course_id": self.course.id.to_deprecated_string(), "enrollment_action": "add_to_cart"},
     )
     request.user = self.user
     response = change_enrollment(request)
     self.assertEqual(response.status_code, 200)
     self.assertEqual(response.content, reverse("shoppingcart.views.show_cart"))
     self.assertTrue(
         shoppingcart.models.PaidCourseRegistration.contained_in_order(
             shoppingcart.models.Order.get_cart_for_user(self.user), self.course.id
         )
     )

    def test_change_enrollment_add_to_cart(self):
        request = self.req_factory.post(
            reverse('change_enrollment'), {
                'course_id': self.course.id.to_deprecated_string(),
                'enrollment_action': 'add_to_cart'
            }
        )

        # Add a session to the request
        SessionMiddleware().process_request(request)
        request.session.save()

        request.user = self.user
        response = change_enrollment(request)
        self.assertEqual(response.status_code, 200)
        self.assertEqual(response.content, reverse('shoppingcart.views.show_cart'))
        self.assertTrue(shoppingcart.models.PaidCourseRegistration.contained_in_order(
            shoppingcart.models.Order.get_cart_for_user(self.user), self.course.id))

    def test_enrollment_limit_by_domain(self):
        """
            Tests that the enrollmentDomain setting is properly limiting enrollment to those who have
            the proper external auth
        """

        # create 2 course, one with limited enrollment one without
        shib_course = CourseFactory.create(org="Stanford", number="123", display_name="Shib Only")
        shib_course.enrollment_domain = "shib:https://idp.stanford.edu/"
        self.store.update_item(shib_course, "**replace_user**")

        open_enroll_course = CourseFactory.create(org="MITx", number="999", display_name="Robot Super Course")
        open_enroll_course.enrollment_domain = ""
        self.store.update_item(open_enroll_course, "**replace_user**")

        # create 3 kinds of students, external_auth matching shib_course, external_auth not matching, no external auth
        shib_student = UserFactory.create()
        shib_student.save()
        extauth = ExternalAuthMap(
            external_id="[email protected]",
            external_email="",
            external_domain="shib:https://idp.stanford.edu/",
            external_credentials="",
            user=shib_student,
        )
        extauth.save()

        other_ext_student = UserFactory.create()
        other_ext_student.username = "teststudent2"
        other_ext_student.email = "[email protected]"
        other_ext_student.save()
        extauth = ExternalAuthMap(
            external_id="[email protected]",
            external_email="",
            external_domain="shib:https://other.edu/",
            external_credentials="",
            user=other_ext_student,
        )
        extauth.save()

        int_student = UserFactory.create()
        int_student.username = "teststudent3"
        int_student.email = "[email protected]"
        int_student.save()

        # Tests the two case for courses, limited and not
        for course in [shib_course, open_enroll_course]:
            for student in [shib_student, other_ext_student, int_student]:
                request = self.request_factory.post("/change_enrollment")
                request.POST.update({"enrollment_action": "enroll", "course_id": course.id})
                request.user = student
                response = change_enrollment(request)
                # If course is not limited or student has correct shib extauth then enrollment should be allowed
                if course is open_enroll_course or student is shib_student:
                    self.assertEqual(response.status_code, 200)
                    self.assertTrue(CourseEnrollment.is_enrolled(student, course.id))
                    # Clean up
                    CourseEnrollment.unenroll(student, course.id)
                else:
                    self.assertEqual(response.status_code, 400)
                    self.assertFalse(CourseEnrollment.is_enrolled(student, course.id))

def course_enroll(request):
    response = change_enrollment(request)
    if isinstance(response, (HttpResponseBadRequest, HttpResponseForbidden)):
        return JsonResponse({ 'status': False, 'reason': response.content })
    else:
        return JsonResponse({ 'status': True })