from cPickle import loads, dumps

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

from django.conf import settings

import redis

class SessionStore(SessionBase):

    """

    A redis-based session store.

    """

    def __init__(self, session_key=None):

        self.redis = redis.Redis(

            host=getattr(settings, "REDIS_HOST", None),

            port=getattr(settings, "REDIS_PORT", None),

            timeout=getattr(settings, "REDIS_TIMEOUT", None),

            db=getattr(settings, "REDIS_DB", None))

        self.redis.connect()

        super(SessionStore, self).__init__(session_key)

    def load(self):

        session_data = self.redis.get(self.session_key)

        if session_data is not None:

            return loads(session_data)

        self.create()

        return {}

    def create(self):

        while True:

            self.session_key = self._get_new_session_key()

            try:

                self.save(must_create=True)

            except CreateError:

                # Would be raised if the key wasn't unique

                continue

            self.modified = True

            return

    def save(self, must_create=False):

        if must_create:

            # preserve=True -> SETNX

            result = self.redis.set(

                self.session_key, dumps(self._get_session(no_load=must_create)), preserve=True)

            if result == 0: # 0 == not created, 1 == created.

                raise CreateError

        else:

            self.redis.set(self.session_key, dumps(self._get_session(no_load=must_create)),)

    def exists(self, session_key):

        if self.redis.exists(session_key):

            return True

        return False

    def delete(self, session_key=None):

        if session_key is None:

            if self._session_key is None:

                return

            session_key = self._session_key

        self.redis.delete(session_key)