from Common import *


class SessionStore(Object):
    """A general session store.

    SessionStores are dictionary-like objects used by Application to
    store session state. This class is abstract and it's up to the
    concrete subclass to implement several key methods that determine
    how sessions are stored (such as in memory, on disk or in a
    database).

    Subclasses often encode sessions for storage somewhere. In light
    of that, this class also defines methods encoder(), decoder() and
    setEncoderDecoder(). The encoder and decoder default to the load()
    and dump() functions of the cPickle or pickle module. However,
    using the setEncoderDecoder() method, you can use the functions
    from marshal (if appropriate) or your own encoding scheme.
    Subclasses should use encoder() and decoder() (and not
    pickle.load() and pickle.dump()).

    Subclasses may rely on the attribute self._app to point to the
    application.

    Subclasses should be named SessionFooStore since Application
    expects "Foo" to appear for the "SessionStore" setting and
    automatically prepends Session and appends Store. Currently, you
    will also need to add another import statement in Application.py.
    Search for SessionStore and you'll find the place.

    TO DO

    * Should there be a check-in/check-out strategy for sessions to
      prevent concurrent requests on the same session? If so, that can
      probably be done at this level (as opposed to pushing the burden
      on various subclasses).

    """


    ## Init ##

    def __init__(self, app):
        """ Subclasses must invoke super. """
        Object.__init__(self)
        self._app = app
        try:
            import cPickle as pickle
        except ImportError:
            import pickle
        if hasattr(pickle, 'HIGHEST_PROTOCOL'):
            def dumpWithHighestProtocol(obj, f,
                    proto=pickle.HIGHEST_PROTOCOL, dump=pickle.dump):
                return dump(obj, f, proto)
            self._encoder = dumpWithHighestProtocol
        else:
            self._encoder = pickle.dump
        self._decoder = pickle.load


    ## Access ##

    def application(self):
        return self._app


    ## Dictionary-style access ##

    def __len__(self):
        raise AbstractError, self.__class__

    def __getitem__(self, key):
        raise AbstractError, self.__class__

    def __setitem__(self, key, item):
        raise AbstractError, self.__class__

    def __delitem__(self, key):
        """Delete an item.

        Subclasses are responsible for expiring the session as well.
        Something along the lines of:
            sess = self[key]
            if not sess.isExpired():
                sess.expiring()

        """
        raise AbstractError, self.__class__

    def has_key(self, key):
        raise AbstractError, self.__class__

    def keys(self):
        raise AbstractError, self.__class__

    def clear(self):
        raise AbstractError, self.__class__

    def setdefault(self, key, default):
        raise AbstractError, self.__class__


    ## Application support ##

    def storeSession(self, session):
        raise AbstractError, self.__class__

    def storeAllSessions(self):
        raise AbstractError, self.__class__

    def cleanStaleSessions(self, task=None):
        """Clean stale sessions.

        Called by the Application to tell this store to clean out all
        sessions that have exceeded their lifetime.

        """
        curTime = time.time()
        for key in self.keys():
            try:
                sess = self[key]
            except KeyError:
                pass # session was already deleted by some other thread
            else:
                if curTime - sess.lastAccessTime() >= sess.timeout() \
                        or sess.timeout() == 0:
                    try:
                        del self[key]
                    except KeyError:
                        pass # already deleted by some other thread


    ## Convenience methods ##

    def items(self):
        itms = []
        for k in self.keys():
            try:
                itms.append((k, self[k]))
            except KeyError:
                # since we aren't using a lock here, some keys
                # could be already deleted again during this loop
                pass
        return itms

    def values(self):
        vals = []
        for k in self.keys():
            try:
                vals.append(self[k])
            except KeyError:
                pass
        return vals

    def get(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            return default


    ## Encoder/decoder ##

    def encoder(self):
        return self._encoder

    def decoder(self):
        return self._decoder

    def setEncoderDecoder(self, encoder, decoder):
        self._encoder = encoder
        self._decoder = decoder


    ## As a string ##

    def __repr__(self):
        d = {}
        for key, value in self.items():
            d[key] = value
        return repr(d)