import time

from django.conf import settings

from django.utils.cache import patch_vary_headers

from django.utils.http import cookie_date

from django.utils.importlib import import_module

class SessionMiddleware(object):

    def process_request(self, request):

        engine = import_module(settings.SESSION_ENGINE)

        session_key = request.COOKIES.get(settings.SESSION_COOKIE_NAME, None)

        request.session = engine.SessionStore(session_key)

    def process_response(self, request, response):

        """

        If request.session was modified, or if the configuration is to save the

        session every time, save the changes and set a session cookie.

        """

        try:

            accessed = request.session.accessed

            modified = request.session.modified

        except AttributeError:

            pass

        else:

            if accessed:

                patch_vary_headers(response, ('Cookie',))

            if modified or settings.SESSION_SAVE_EVERY_REQUEST:

                if request.session.get_expire_at_browser_close():

                    max_age = None

                    expires = None

                else:

                    max_age = request.session.get_expiry_age()

                    expires_time = time.time() + max_age

                    expires = cookie_date(expires_time)

                # Save the session data and refresh the client cookie.

                request.session.save()

                response.set_cookie(settings.SESSION_COOKIE_NAME,

                        request.session.session_key, max_age=max_age,

                        expires=expires, domain=settings.SESSION_COOKIE_DOMAIN,

                        path=settings.SESSION_COOKIE_PATH,

                        secure=settings.SESSION_COOKIE_SECURE or None)

        return response