import os

import tempfile

from django.conf import settings

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

from django.core.exceptions import SuspiciousOperation, ImproperlyConfigured

class SessionStore(SessionBase):

    """

    Implements a file based session store.

    """

    def __init__(self, session_key=None):

        self.storage_path = getattr(settings, "SESSION_FILE_PATH", None)

        if not self.storage_path:

            self.storage_path = tempfile.gettempdir()

        # Make sure the storage path is valid.

        if not os.path.isdir(self.storage_path):

            raise ImproperlyConfigured("The session storage path %r doesn't exist. "\

                                       "Please set your SESSION_FILE_PATH setting "\

                                       "to an existing directory in which Django "\

                                       "can store session data." % self.storage_path)

        self.file_prefix = settings.SESSION_COOKIE_NAME

        super(SessionStore, self).__init__(session_key)

    def _key_to_file(self, session_key=None):

        """

        Get the file associated with this session key.

        """

        if session_key is None:

            session_key = self.session_key

        # Make sure we're not vulnerable to directory traversal. Session keys

        # should always be md5s, so they should never contain directory components.

        if os.path.sep in session_key:

            raise SuspiciousOperation("Invalid characters (directory components) in session key")

        return os.path.join(self.storage_path, self.file_prefix + session_key)

    def load(self):

        session_data = {}

        try:

            session_file = open(self._key_to_file(), "rb")

            try:

                try:

                    session_data = self.decode(session_file.read())

                except(EOFError, SuspiciousOperation):

                    self._session_key = self._get_new_session_key()

                    self._session_cache = {}

                    self.save()

                    # Ensure the user is notified via a new cookie.

                    self.modified = True

            finally:

                session_file.close()

        except(IOError):

            pass

        return session_data

    def save(self):

        try:

            f = open(self._key_to_file(self.session_key), "wb")

            try:

                f.write(self.encode(self._session))

            finally:

                f.close()

        except(IOError, EOFError):

            pass

    def exists(self, session_key):

        if os.path.exists(self._key_to_file(session_key)):

            return True

        return False

    def delete(self, session_key):

        try:

            os.unlink(self._key_to_file(session_key))

        except OSError:

            pass

    def clean(self):

        pass