from django.conf import settings

from django.contrib.messages.storage import default_storage

class MessageMiddleware(object):

    """

    Middleware that handles temporary messages.

    """

    def process_request(self, request):

        request._messages = default_storage(request)

    def process_response(self, request, response):

        """

        Updates the storage backend (i.e., saves the messages).

        If not all messages could not be stored and ``DEBUG`` is ``True``, a

        ``ValueError`` is raised.

        """

        # A higher middleware layer may return a request which does not contain

        # messages storage, so make no assumption that it will be there.

        if hasattr(request, '_messages'):

            unstored_messages = request._messages.update(response)

            if unstored_messages and settings.DEBUG:

                raise ValueError('Not all temporary messages could be stored.')

        return response