def _delete_item_at_location(item_location, delete_children=False, delete_all_versions=False, user=None):
    """
    Deletes the item at with the given Location.

    It is assumed that course permissions have already been checked.
    """
    store = get_modulestore(item_location)

    item = store.get_item(item_location)

    if delete_children:
        _xmodule_recurse(item, lambda i: store.delete_item(i.location, delete_all_versions=delete_all_versions))
    else:
        store.delete_item(item.location, delete_all_versions=delete_all_versions)

    # cdodge: we need to remove our parent's pointer to us so that it is no longer dangling
    if delete_all_versions:
        parent_locs = modulestore('direct').get_parent_locations(item_location, None)

        item_url = item_location.url()
        for parent_loc in parent_locs:
            parent = modulestore('direct').get_item(parent_loc)
            parent.children.remove(item_url)
            modulestore('direct').update_item(parent, user.id if user else None)

    return JsonResponse()

    def test_fail_for_non_video_module(self):
        # Video module: setup
        data = {
            'parent_locator': unicode(self.course.location),
            'category': 'videoalpha',
            'type': 'videoalpha'
        }
        resp = self.client.ajax_post('/xblock/', data)
        usage_key = self._get_usage_key(resp)
        subs_id = str(uuid4())
        item = modulestore().get_item(usage_key)
        item.data = textwrap.dedent("""
            <videoalpha youtube="" sub="{}">
                <source src="http://www.quirksmode.org/html5/videos/big_buck_bunny.mp4"/>
                <source src="http://www.quirksmode.org/html5/videos/big_buck_bunny.webm"/>
                <source src="http://www.quirksmode.org/html5/videos/big_buck_bunny.ogv"/>
            </videoalpha>
        """.format(subs_id))
        modulestore().update_item(item, self.user.id)

        subs = {
            'start': [100, 200, 240],
            'end': [200, 240, 380],
            'text': [
                'subs #1',
                'subs #2',
                'subs #3'
            ]
        }
        self.save_subs_to_store(subs, subs_id)

        link = reverse('download_transcripts')
        resp = self.client.get(link, {'locator': unicode(usage_key)})
        self.assertEqual(resp.status_code, 404)

def _upload_asset(request, course_key):
    '''
    This method allows for POST uploading of files into the course asset
    library, which will be supported by GridFS in MongoDB.
    '''
    # Does the course actually exist?!? Get anything from it to prove its
    # existence
    try:
        modulestore().get_course(course_key)
    except ItemNotFoundError:
        # no return it as a Bad Request response
        logging.error("Could not find course: %s", course_key)
        return HttpResponseBadRequest()

    # compute a 'filename' which is similar to the location formatting, we're
    # using the 'filename' nomenclature since we're using a FileSystem paradigm
    # here. We're just imposing the Location string formatting expectations to
    # keep things a bit more consistent
    upload_file = request.FILES['file']
    filename = upload_file.name
    mime_type = upload_file.content_type

    content_loc = StaticContent.compute_location(course_key, filename)

    chunked = upload_file.multiple_chunks()
    sc_partial = partial(StaticContent, content_loc, filename, mime_type)
    if chunked:
        content = sc_partial(upload_file.chunks())
        tempfile_path = upload_file.temporary_file_path()
    else:
        content = sc_partial(upload_file.read())
        tempfile_path = None

    # first let's see if a thumbnail can be created
    (thumbnail_content, thumbnail_location) = contentstore().generate_thumbnail(
            content,
            tempfile_path=tempfile_path
    )

    # delete cached thumbnail even if one couldn't be created this time (else
    # the old thumbnail will continue to show)
    del_cached_content(thumbnail_location)
    # now store thumbnail location only if we could create it
    if thumbnail_content is not None:
        content.thumbnail_location = thumbnail_location

    # then commit the content
    contentstore().save(content)
    del_cached_content(content.location)

    # readback the saved content - we need the database timestamp
    readback = contentstore().find(content.location)

    locked = getattr(content, 'locked', False)
    response_payload = {
        'asset': _get_asset_json(content.name, readback.last_modified_at, content.location, content.thumbnail_location, locked),
        'msg': _('Upload completed')
    }

    return JsonResponse(response_payload)

    def clean_course_id(self):
        """Validate the course id"""
        cleaned_id = self.cleaned_data["course_id"]
        try:
            course_key = CourseKey.from_string(cleaned_id)
        except InvalidKeyError:
            try:
                course_key = SlashSeparatedCourseKey.from_deprecated_string(cleaned_id)
            except InvalidKeyError:
                msg = u'Course id invalid.'
                msg += u' --- Entered course id was: "{0}". '.format(cleaned_id)
                msg += 'Please recheck that you have supplied a valid course id.'
                raise forms.ValidationError(msg)

        if not modulestore().has_course(course_key):
            msg = u'COURSE NOT FOUND'
            msg += u' --- Entered course id was: "{0}". '.format(course_key.to_deprecated_string())
            msg += 'Please recheck that you have supplied a valid course id.'
            raise forms.ValidationError(msg)

        # Now, try and discern if it is a Studio course - HTML editor doesn't work with XML courses
        is_studio_course = modulestore().get_modulestore_type(course_key) != ModuleStoreEnum.Type.xml
        if not is_studio_course:
            msg = "Course Email feature is only available for courses authored in Studio. "
            msg += '"{0}" appears to be an XML backed course.'.format(course_key.to_deprecated_string())
            raise forms.ValidationError(msg)

        return course_key

    def update_from_json(cls, descriptor, jsondict, filter_tabs=True, user=None):
        """
        Decode the json into CourseMetadata and save any changed attrs to the db.

        Ensures none of the fields are in the blacklist.
        """
        # Copy the filtered list to avoid permanently changing the class attribute.
        filtered_list = list(cls.FILTERED_LIST)
        # Don't filter on the tab attribute if filter_tabs is False.
        if not filter_tabs:
            filtered_list.remove("tabs")

        # Validate the values before actually setting them.
        key_values = {}

        for key, model in jsondict.iteritems():
            # should it be an error if one of the filtered list items is in the payload?
            if key in filtered_list:
                continue
            try:
                val = model['value']
                if hasattr(descriptor, key) and getattr(descriptor, key) != val:
                    key_values[key] = descriptor.fields[key].from_json(val)
            except (TypeError, ValueError) as err:
                raise ValueError(_("Incorrect format for field '{name}'. {detailed_message}".format(
                    name=model['display_name'], detailed_message=err.message)))

        for key, value in key_values.iteritems():
            setattr(descriptor, key, value)

        if len(key_values) > 0:
            modulestore().update_item(descriptor, user.id if user else None)

        return cls.fetch(descriptor)

    def create(cls, data):
        """
        Create a Bookmark object.

        Arguments:
            data (dict): The data to create the object with.

        Returns:
            A Bookmark object.

        Raises:
            ItemNotFoundError: If no block exists for the usage_key.
        """
        data = dict(data)
        usage_key = data.pop('usage_key')

        with modulestore().bulk_operations(usage_key.course_key):
            block = modulestore().get_item(usage_key)

            xblock_cache = XBlockCache.create({
                'usage_key': usage_key,
                'display_name': block.display_name_with_default,
            })
            data['_path'] = prepare_path_for_serialization(Bookmark.updated_path(usage_key, xblock_cache))

        data['course_key'] = usage_key.course_key
        data['xblock_cache'] = xblock_cache

        user = data.pop('user')

        # Sometimes this ends up in data, but newer versions of Django will fail on having unknown keys in defaults
        data.pop('display_name', None)

        bookmark, created = cls.objects.get_or_create(usage_key=usage_key, user=user, defaults=data)
        return bookmark, created

 def _fulfill_content_milestones(user, course_key, content_key):
     """
     Internal helper to handle milestone fulfillments for the specified content module
     """
     # Fulfillment Use Case: Entrance Exam
     # If this module is part of an entrance exam, we'll need to see if the student
     # has reached the point at which they can collect the associated milestone
     if settings.FEATURES.get('ENTRANCE_EXAMS', False):
         course = modulestore().get_course(course_key)
         content = modulestore().get_item(content_key)
         entrance_exam_enabled = getattr(course, 'entrance_exam_enabled', False)
         in_entrance_exam = getattr(content, 'in_entrance_exam', False)
         if entrance_exam_enabled and in_entrance_exam:
             # We don't have access to the true request object in this context, but we can use a mock
             request = RequestFactory().request()
             request.user = user
             exam_pct = get_entrance_exam_score(request, course)
             if exam_pct >= course.entrance_exam_minimum_score_pct:
                 exam_key = UsageKey.from_string(course.entrance_exam_id)
                 relationship_types = milestones_helpers.get_milestone_relationship_types()
                 content_milestones = milestones_helpers.get_course_content_milestones(
                     course_key,
                     exam_key,
                     relationship=relationship_types['FULFILLS']
                 )
                 # Add each milestone to the user's set...
                 user = {'id': request.user.id}
                 for milestone in content_milestones:
                     milestones_helpers.add_user_milestone(user, milestone)

def submit_delete_problem_state_for_all_students(request, usage_key):  # pylint: disable=invalid-name
    """
    Request to have state deleted for a problem as a background task.

    The problem's state will be deleted for all students who have accessed the
    particular problem in a course.  Parameters are the `course_id` and
    the `usage_key`, which must be a :class:`Location`.

    ItemNotFoundException is raised if the problem doesn't exist, or AlreadyRunningError
    if the particular problem's state is already being deleted.

    This method makes sure the InstructorTask entry is committed.
    When called from any view that is wrapped by TransactionMiddleware,
    and thus in a "commit-on-success" transaction, an autocommit buried within here
    will cause any pending transaction to be committed by a successful
    save here.  Any future database operations will take place in a
    separate transaction.
    """
    # check arguments:  make sure that the usage_key is defined
    # (since that's currently typed in).  If the corresponding module descriptor doesn't exist,
    # an exception will be raised.  Let it pass up to the caller.
    modulestore().get_item(usage_key)

    task_type = 'delete_problem_state'
    task_class = delete_problem_state
    task_input, task_key = encode_problem_and_student_input(usage_key)
    return submit_task(request, task_type, task_class, usage_key.course_key, task_input, task_key)

def _get_module_info(xblock, rewrite_static_links=True, include_ancestor_info=False, include_publishing_info=False):
    """
    metadata, data, id representation of a leaf module fetcher.
    :param usage_key: A UsageKey
    """
    with modulestore().bulk_operations(xblock.location.course_key):
        data = getattr(xblock, 'data', '')
        if rewrite_static_links:
            data = replace_static_urls(
                data,
                None,
                course_id=xblock.location.course_key
            )

        # Pre-cache has changes for the entire course because we'll need it for the ancestor info
        # Except library blocks which don't [yet] use draft/publish
        if not isinstance(xblock.location, LibraryUsageLocator):
            modulestore().has_changes(modulestore().get_course(xblock.location.course_key, depth=None))

        # Note that children aren't being returned until we have a use case.
        xblock_info = create_xblock_info(
            xblock, data=data, metadata=own_metadata(xblock), include_ancestor_info=include_ancestor_info
        )
        if include_publishing_info:
            add_container_page_publishing_info(xblock, xblock_info)
        return xblock_info

    def instrument_course_progress_render(self, course_width, enable_ccx, queries, reads, xblocks):
        """
        Renders the progress page, instrumenting Mongo reads and SQL queries.
        """
        self.setup_course(course_width, enable_ccx)

        # Switch to published-only mode to simulate the LMS
        with self.settings(MODULESTORE_BRANCH='published-only'):
            # Clear all caches before measuring
            for cache in settings.CACHES:
                get_cache(cache).clear()

            # Refill the metadata inheritance cache
            modulestore().get_course(self.course.id, depth=None)

            # We clear the request cache to simulate a new request in the LMS.
            RequestCache.clear_request_cache()

            # Reset the list of provider classes, so that our django settings changes
            # can actually take affect.
            OverrideFieldData.provider_classes = None

            with self.assertNumQueries(queries):
                with check_mongo_calls(reads):
                    with check_sum_of_calls(XBlock, ['__init__'], xblocks, xblocks, include_arguments=False):
                        self.grade_course(self.course)

def component_handler(request, usage_key_string, handler, suffix=''):
    """
    Dispatch an AJAX action to an xblock

    Args:
        usage_id: The usage-id of the block to dispatch to
        handler (str): The handler to execute
        suffix (str): The remainder of the url to be passed to the handler

    Returns:
        :class:`django.http.HttpResponse`: The response from the handler, converted to a
            django response
    """

    usage_key = UsageKey.from_string(usage_key_string)

    descriptor = modulestore().get_item(usage_key)
    # Let the module handle the AJAX
    req = django_to_webob_request(request)

    try:
        resp = descriptor.handle(handler, req, suffix)

    except NoSuchHandlerError:
        log.info("XBlock %s attempted to access missing handler %r", descriptor, handler, exc_info=True)
        raise Http404

    # unintentional update to handle any side effects of handle call; so, request user didn't author
    # the change
    modulestore().update_item(descriptor, None)

    return webob_to_django_response(resp)

def handle_xblock_callback(request, course_id, usage_id, handler, suffix=None):
    """
    Generic view for extensions. This is where AJAX calls go.

    Arguments:

      - request -- the django request.
      - location -- the module location. Used to look up the XModule instance
      - course_id -- defines the course context for this request.

    Return 403 error if the user is not logged in. Raises Http404 if
    the location and course_id do not identify a valid module, the module is
    not accessible by the user, or the module raises NotFoundError. If the
    module raises any other error, it will escape this function.
    """
    if not request.user.is_authenticated():
        return HttpResponse('Unauthenticated', status=403)

    try:
        course_key = CourseKey.from_string(course_id)
    except InvalidKeyError:
        raise Http404("Invalid location")

    with modulestore().bulk_operations(course_key):
        try:
            course = modulestore().get_course(course_key)
        except ItemNotFoundError:
            raise Http404("invalid location")

        return _invoke_xblock_handler(request, course_id, usage_id, handler, suffix, course=course)

def orphan_handler(request, tag=None, package_id=None, branch=None, version_guid=None, block=None):
    """
    View for handling orphan related requests. GET gets all of the current orphans.
    DELETE removes all orphans (requires is_staff access)

    An orphan is a block whose category is not in the DETACHED_CATEGORY list, is not the root, and is not reachable
    from the root via children

    :param request:
    :param package_id: Locator syntax package_id
    """
    location = BlockUsageLocator(package_id=package_id, branch=branch, version_guid=version_guid, block_id=block)
    # DHM: when split becomes back-end, move or conditionalize this conversion
    old_location = loc_mapper().translate_locator_to_location(location)
    if request.method == 'GET':
        if has_course_access(request.user, old_location):
            return JsonResponse(modulestore().get_orphans(old_location, 'draft'))
        else:
            raise PermissionDenied()
    if request.method == 'DELETE':
        if request.user.is_staff:
            items = modulestore().get_orphans(old_location, 'draft')
            for itemloc in items:
                modulestore('draft').delete_item(itemloc, delete_all_versions=True)
            return JsonResponse({'deleted': items})
        else:
            raise PermissionDenied()

 def test_group(self):
     self.course.cohort_config = {"cohorted": True}
     modulestore().update_item(self.course, ModuleStoreEnum.UserID.test)
     cohort = CohortFactory.create(course_id=self.course.id)
     serialized = self.serialize(self.make_cs_content({"group_id": cohort.id}))
     self.assertEqual(serialized["group_id"], cohort.id)
     self.assertEqual(serialized["group_name"], cohort.name)

def submit_delete_entrance_exam_state_for_student(request, usage_key, student):  # pylint: disable=invalid-name
    """
    Requests reset of state for entrance exam as a background task.

    Module state for all problems in entrance exam will be deleted
    for specified student.

    Parameters are `usage_key`, which must be a :class:`Location`
    representing entrance exam section and the `student` as a User object.

    ItemNotFoundError is raised if entrance exam does not exists for given
    usage_key, AlreadyRunningError is raised if the entrance exam
    is already being reset.

    This method makes sure the InstructorTask entry is committed.
    When called from any view that is wrapped by TransactionMiddleware,
    and thus in a "commit-on-success" transaction, an autocommit buried within here
    will cause any pending transaction to be committed by a successful
    save here.  Any future database operations will take place in a
    separate transaction.
    """
    # check arguments:  make sure entrance exam(section) exists for given usage_key
    modulestore().get_item(usage_key)

    task_type = 'delete_problem_state'
    task_class = delete_problem_state
    task_input, task_key = encode_entrance_exam_and_student_input(usage_key, student)
    return submit_task(request, task_type, task_class, usage_key.course_key, task_input, task_key)

    def test_get_items(self):
        '''
        This verifies a bug we had where the None setting in get_items() meant 'wildcard'
        Unfortunately, None = published for the revision field, so get_items() would return
        both draft and non-draft copies.
        '''
        store = modulestore('direct')
        draft_store = modulestore('draft')
        import_from_xml(store, 'common/test/data/', ['simple'])

        html_module = draft_store.get_item(['i4x', 'edX', 'simple', 'html', 'test_html', None])

        draft_store.clone_item(html_module.location, html_module.location)

        # now query get_items() to get this location with revision=None, this should just
        # return back a single item (not 2)

        items = store.get_items(['i4x', 'edX', 'simple', 'html', 'test_html', None])
        self.assertEqual(len(items), 1)
        self.assertFalse(getattr(items[0], 'is_draft', False))

        # now refetch from the draft store. Note that even though we pass
        # None in the revision field, the draft store will replace that with 'draft'
        items = draft_store.get_items(['i4x', 'edX', 'simple', 'html', 'test_html', None])
        self.assertEqual(len(items), 1)
        self.assertTrue(getattr(items[0], 'is_draft', False))

def component_handler(request, usage_id, handler, suffix=""):
    """
    Dispatch an AJAX action to an xblock

    Args:
        usage_id: The usage-id of the block to dispatch to, passed through `quote_slashes`
        handler (str): The handler to execute
        suffix (str): The remainder of the url to be passed to the handler

    Returns:
        :class:`django.http.HttpResponse`: The response from the handler, converted to a
            django response
    """

    location = unquote_slashes(usage_id)

    descriptor = modulestore().get_item(location)
    # Let the module handle the AJAX
    req = django_to_webob_request(request)

    try:
        resp = descriptor.handle(handler, req, suffix)

    except NoSuchHandlerError:
        log.info("XBlock %s attempted to access missing handler %r", descriptor, handler, exc_info=True)
        raise Http404

    modulestore().save_xmodule(descriptor)

    return webob_to_django_response(resp)

    def handle(self, *args, **options):
        "Execute the command"
        if len(args) == 0:
            raise CommandError("import requires at least one argument: <data directory> [--nostatic] [<course dir>...]")

        data_dir = args[0]
        do_import_static = not (options.get('nostatic', False))
        if len(args) > 1:
            course_dirs = args[1:]
        else:
            course_dirs = None
        self.stdout.write("Importing.  Data_dir={data}, course_dirs={courses}\n".format(
            data=data_dir,
            courses=course_dirs,
            dis=do_import_static))
        try:
            mstore = modulestore('direct')
        except KeyError:
            self.stdout.write('Unable to load direct modulestore, trying '
                              'default\n')
            mstore = modulestore('default')

        _, course_items = import_from_xml(
            mstore, data_dir, course_dirs, load_error_modules=False,
            static_content_store=contentstore(), verbose=True,
            do_import_static=do_import_static,
            create_new_course_if_not_present=True,
        )

        for course in course_items:
            course_id = course.id
            if not are_permissions_roles_seeded(course_id):
                self.stdout.write('Seeding forum roles for course {0}\n'.format(course_id))
                seed_permissions_roles(course_id)

    def test_no_ol_course_update(self):
        '''Test trying to add to a saved course_update which is not an ol.'''
        # get the updates and set to something wrong
        location = self.course.location.replace(category='course_info', name='updates')
        modulestore('direct').create_and_save_xmodule(location)
        course_updates = modulestore('direct').get_item(location)
        course_updates.data = 'bad news'
        modulestore('direct').update_item(location, course_updates.data)

        init_content = '<iframe width="560" height="315" src="http://www.youtube.com/embed/RocY-Jd93XU" frameborder="0">'
        content = init_content + '</iframe>'
        payload = {'content': content,
                   'date': 'January 8, 2013'}
        url = reverse('course_info_json',
                      kwargs={'org': self.course.location.org,
                              'course': self.course.location.course,
                              'provided_id': ''})

        resp = self.client.post(url, json.dumps(payload), "application/json")

        payload = json.loads(resp.content)

        self.assertHTMLEqual(payload['content'], content)

        # now confirm that the bad news and the iframe make up 2 updates
        url = reverse('course_info_json',
                      kwargs={'org': self.course.location.org,
                              'course': self.course.location.course,
                              'provided_id': ''})
        resp = self.client.get(url)
        payload = json.loads(resp.content)
        self.assertTrue(len(payload) == 2)

def find_peer_grading_module(course):
    """
    Given a course, finds the first peer grading module in it.
    @param course: A course object.
    @return: boolean found_module, string problem_url
    """

    # Reverse the base course url.
    base_course_url = reverse("courses")
    found_module = False
    problem_url = ""

    # Get the peer grading modules currently in the course.  Explicitly specify the course id to avoid issues with different runs.
    items = modulestore().get_items(course.id, category="peergrading")
    # See if any of the modules are centralized modules (ie display info from multiple problems)
    items = [i for i in items if not getattr(i, "use_for_single_location", True)]
    # Loop through all potential peer grading modules, and find the first one that has a path to it.
    for item in items:
        # Generate a url for the first module and redirect the user to it.
        try:
            problem_url_parts = search.path_to_location(modulestore(), item.location)
        except NoPathToItem:
            # In the case of nopathtoitem, the peer grading module that was found is in an invalid state, and
            # can no longer be accessed.  Log an informational message, but this will not impact normal behavior.
            log.info(
                u"Invalid peer grading module location {0} in course {1}.  This module may need to be removed.".format(
                    item_location, course.id
                )
            )
            continue
        problem_url = generate_problem_url(problem_url_parts, base_course_url)
        found_module = True

    return found_module, problem_url