"""a plugin that emulates 0.1 Session behavior."""

import sqlalchemy.orm.objectstore as objectstore
import sqlalchemy.orm.unitofwork as unitofwork
import sqlalchemy.util as util
import sqlalchemy

import sqlalchemy.mods.threadlocal

class LegacySession(objectstore.Session):
    def __init__(self, nest_on=None, hash_key=None, **kwargs):
        super(LegacySession, self).__init__(**kwargs)
        self.parent_uow = None
        self.begin_count = 0
        self.nest_on = util.to_list(nest_on)
        self.__pushed_count = 0
    def was_pushed(self):
        if self.nest_on is None:
            return
        self.__pushed_count += 1
        if self.__pushed_count == 1:
            for n in self.nest_on:
                n.push_session()
    def was_popped(self):
        if self.nest_on is None or self.__pushed_count == 0:
            return
        self.__pushed_count -= 1
        if self.__pushed_count == 0:
            for n in self.nest_on:
                n.pop_session()
    class SessionTrans(object):
        """returned by Session.begin(), denotes a transactionalized UnitOfWork instance.
        call commit() on this to commit the transaction."""
        def __init__(self, parent, uow, isactive):
            self.__parent = parent
            self.__isactive = isactive
            self.__uow = uow
        isactive = property(lambda s:s.__isactive, doc="True if this SessionTrans is the 'active' transaction marker, else its a no-op.")
        parent = property(lambda s:s.__parent, doc="returns the parent Session of this SessionTrans object.")
        uow = property(lambda s:s.__uow, doc="returns the parent UnitOfWork corresponding to this transaction.")
        def begin(self):
            """calls begin() on the underlying Session object, returning a new no-op SessionTrans object."""
            if self.parent.uow is not self.uow:
                raise InvalidRequestError("This SessionTrans is no longer valid")
            return self.parent.begin()
        def commit(self):
            """commits the transaction noted by this SessionTrans object."""
            self.__parent._trans_commit(self)
            self.__isactive = False
        def rollback(self):
            """rolls back the current UnitOfWork transaction, in the case that begin()
            has been called.  The changes logged since the begin() call are discarded."""
            self.__parent._trans_rollback(self)
            self.__isactive = False
    def begin(self):
        """begins a new UnitOfWork transaction and returns a tranasaction-holding
        object.  commit() or rollback() should be called on the returned object.
        commit() on the Session will do nothing while a transaction is pending, and further
        calls to begin() will return no-op transactional objects."""
        if self.parent_uow is not None:
            return LegacySession.SessionTrans(self, self.uow, False)
        self.parent_uow = self.uow
        self.uow = unitofwork.UnitOfWork(identity_map = self.uow.identity_map)
        return LegacySession.SessionTrans(self, self.uow, True)
    def commit(self, *objects):
        """commits the current UnitOfWork transaction.  called with
        no arguments, this is only used
        for "implicit" transactions when there was no begin().
        if individual objects are submitted, then only those objects are committed, and the 
        begin/commit cycle is not affected."""
        # if an object list is given, commit just those but dont
        # change begin/commit status
        if len(objects):
            self._commit_uow(*objects)
            self.uow.flush(self, *objects)
            return
        if self.parent_uow is None:
            self._commit_uow()
    def _trans_commit(self, trans):
        if trans.uow is self.uow and trans.isactive:
            try:
                self._commit_uow()
            finally:
                self.uow = self.parent_uow
                self.parent_uow = None
    def _trans_rollback(self, trans):
        if trans.uow is self.uow:
            self.uow = self.parent_uow
            self.parent_uow = None
    def _commit_uow(self, *obj):
        self.was_pushed()
        try:
            self.uow.flush(self, *obj)
        finally:
            self.was_popped()

def begin():
    """deprecated.  use s = Session(new_imap=False)."""
    return objectstore.get_session().begin()

def commit(*obj):
    """deprecated; use flush(*obj)"""
    objectstore.get_session().flush(*obj)

def uow():
    return objectstore.get_session()

def push_session(sess):
    old = get_session()
    if getattr(sess, '_previous', None) is not None:
        raise InvalidRequestError("Given Session is already pushed onto some thread's stack")
    sess._previous = old
    session_registry.set(sess)
    sess.was_pushed()

def pop_session():
    sess = get_session()
    old = sess._previous
    sess._previous = None
    session_registry.set(old)
    sess.was_popped()
    return old

def using_session(sess, func):
    push_session(sess)
    try:
        return func()
    finally:
        pop_session()

def install_plugin():
    objectstore.Session = LegacySession
    objectstore.session_registry = util.ScopedRegistry(objectstore.Session)
    objectstore.begin = begin
    objectstore.commit = commit
    objectstore.uow = uow
    objectstore.push_session = push_session
    objectstore.pop_session = pop_session
    objectstore.using_session = using_session
install_plugin()