def _change_state(session, x, oldstate, newstate):

    nocheck = session.transaction_data.setdefault('skip-security', set())

    nocheck.add((x, 'in_state', oldstate))

    nocheck.add((x, 'in_state', newstate))

    # delete previous state first in case we're using a super session

    session.delete_relation(x, 'in_state', oldstate)

    session.add_relation(x, 'in_state', newstate)

        pendingeids = session.transaction_data.get('pendingeids', ())

        if not (session.deleted_in_transaction(entity.eid) or entity.in_state) \

               and entity.current_workflow:

            state = entity.current_workflow.initial

            if state:

                # use super session to by-pass security checks

                session.super_session.add_relation(entity.eid, 'in_state',

                                                   state.eid)

class _WorkflowChangedOp(hook.Operation):

    """fix entity current state when changing its workflow"""

    def precommit_event(self):

        session = self.session

        if session.deleted_in_transaction(self.eid):

            return

        entity = session.entity_from_eid(self.eid)

        # notice that enforcment that new workflow apply to the entity's type is

        # done by schema rule, no need to check it here

        if entity.current_workflow.eid == self.wfeid:

            deststate = entity.current_workflow.initial

            if not deststate:

                msg = session._('workflow has no initial state')

                raise ValidationError(entity.eid, {'custom_workflow': msg})

            if entity.current_workflow.state_by_eid(entity.current_state.eid):

                # nothing to do

                return

            # if there are no history, simply go to new workflow's initial state

            if not entity.workflow_history:

                if entity.current_state.eid != deststate.eid:

                    _change_state(session, entity.eid,

                                  entity.current_state.eid, deststate.eid)

                return

            msg = session._('workflow changed to "%s"')

            msg %= entity.current_workflow.name

            entity.change_state(deststate.name, msg)

class FireTransitionHook(WorkflowHook):

    """check the transition is allowed, add missing information. Expect that:

    * wf_info_for inlined relation is set

    * by_transition or to_state (managers only) inlined relation is set

    """

    __select__ = WorkflowHook.__select__ & entity_implements('TrInfo')

    events = ('before_add_entity',)

        entity = self.entity

        # first retreive entity to which the state change apply

        try:

            foreid = entity['wf_info_for']

        except KeyError:

            msg = session._('mandatory relation')

            raise ValidationError(entity.eid, {'wf_info_for': msg})

        forentity = session.entity_from_eid(foreid)

        # then check it has a workflow set

        wf = forentity.current_workflow

        if wf is None:

            msg = session._('related entity has no workflow set')

            raise ValidationError(entity.eid, {None: msg})

        # then check it has a state set

        fromstate = forentity.current_state

        if fromstate is None:

            msg = session._('related entity has no state')

            raise ValidationError(entity.eid, {None: msg})

        # no investigate the requested state change...

        try:

            treid = entity['by_transition']

        except KeyError:

            # no transition set, check user is a manager and destination state is

            # specified (and valid)

            if not (session.is_super_session or 'managers' in session.user.groups):

                msg = session._('mandatory relation')

                raise ValidationError(entity.eid, {'by_transition': msg})

            deststateeid = entity.get('to_state')

            if not deststateeid:

                msg = session._('mandatory relation')

                raise ValidationError(entity.eid, {'by_transition': msg})

            deststate = wf.state_by_eid(deststateeid)

            if deststate is None:

                msg = session._("state doesn't belong to entity's workflow")

                raise ValidationError(entity.eid, {'to_state': msg})

        else:

            # check transition is valid and allowed

            tr = wf.transition_by_eid(treid)

            if tr is None:

                msg = session._("transition doesn't belong to entity's workflow")

                raise ValidationError(entity.eid, {'by_transition': msg})

            if not tr.has_input_state(fromstate):

                msg = session._("transition isn't allowed")

                raise ValidationError(entity.eid, {'by_transition': msg})

            if not tr.may_be_fired(foreid):

                msg = session._("transition may not be fired")

                raise ValidationError(entity.eid, {'by_transition': msg})

            deststateeid = tr.destination().eid

        # everything is ok, add missing information on the trinfo entity

        entity['from_state'] = fromstate.eid

        entity['to_state'] = deststateeid

        nocheck = session.transaction_data.setdefault('skip-security', set())

        nocheck.add((entity.eid, 'from_state', fromstate.eid))

        nocheck.add((entity.eid, 'to_state', deststateeid))

class FiredTransitionHook(WorkflowHook):

    """change related entity state"""

    __id__ = 'wffiretransition'

    __select__ = WorkflowHook.__select__ & entity_implements('TrInfo')

    events = ('after_add_entity',)

    def __call__(self):

        _change_state(self._cw, self.entity['wf_info_for'],

                      self.entity['from_state'], self.entity['to_state'])

class SetCustomWorkflow(WorkflowHook):

    __id__ = 'wfsetcustom'

    __select__ = WorkflowHook.__select__ & hook.match_rtype('custom_workflow')

    events = ('after_add_relation',)

    def __call__(self):

        _WorkflowChangedOp(self._cw, eid=self.eidfrom, wfeid=self.eidto)

class DelCustomWorkflow(SetCustomWorkflow):

    __id__ = 'wfdelcustom'

    events = ('after_delete_relation',)

    def __call__(self):

        entity = self._cw.entity_from_eid(self.eidfrom)

        typewf = entity.cwetype_workflow()

        if typewf is not None:

            _WorkflowChangedOp(self._cw, eid=self.eidfrom, wfeid=typewf.eid)

class DelWorkflowHook(WorkflowHook):

    __id__ = 'wfdel'

    __select__ = WorkflowHook.__select__ & entity_implements('Workflow')

    events = ('after_delete_entity',)

    def __call__(self):

        # cleanup unused state and transition

        self._cw.execute('DELETE State X WHERE NOT X state_of Y')

        self._cw.execute('DELETE Transition X WHERE NOT X transition_of Y')