import datetime

from django.contrib.sessions.models import Session

from django.contrib.sessions.backends.base import SessionBase, CreateError

from django.core.exceptions import SuspiciousOperation

from django.db import IntegrityError, transaction

from django.utils.encoding import force_unicode

class SessionStore(SessionBase):

    """

    Implements database session store.

    """

    def load(self):

        try:

            s = Session.objects.get(

                session_key = self.session_key,

                expire_date__gt=datetime.datetime.now()

            )

            return self.decode(force_unicode(s.session_data))

        except (Session.DoesNotExist, SuspiciousOperation):

            self.create()

            return {}

    def exists(self, session_key):

        try:

            Session.objects.get(session_key=session_key)

        except Session.DoesNotExist:

            return False

        return True

    def create(self):

        while True:

            self.session_key = self._get_new_session_key()

            try:

                # Save immediately to ensure we have a unique entry in the

                # database.

                self.save(must_create=True)

            except CreateError:

                # Key wasn't unique. Try again.

                continue

            self.modified = True

            self._session_cache = {}

            return

    def save(self, must_create=False):

        """

        Saves the current session data to the database. If 'must_create' is

        True, a database error will be raised if the saving operation doesn't

        create a *new* entry (as opposed to possibly updating an existing

        entry).

        """

        obj = Session(

            session_key = self.session_key,

            session_data = self.encode(self._get_session(no_load=must_create)),

            expire_date = self.get_expiry_date()

        )

        sid = transaction.savepoint()

        try:

            obj.save(force_insert=must_create)

        except IntegrityError:

            if must_create:

                transaction.savepoint_rollback(sid)

                raise CreateError

            raise

    def delete(self, session_key=None):

        if session_key is None:

            if self._session_key is None:

                return

            session_key = self._session_key

        try:

            Session.objects.get(session_key=session_key).delete()

        except Session.DoesNotExist:

            pass