271 lines
8.5 KiB
Python
271 lines
8.5 KiB
Python
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import re
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import inspect
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from .backwardscompat import callable
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# metaclass implementation idea from
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# http://blog.ianbicking.org/more-on-python-metaprogramming-comment-14.html
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_transition_gatherer = []
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def transition(event, from_, to, action=None, guard=None):
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_transition_gatherer.append([event, from_, to, action, guard])
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_state_gatherer = []
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def state(name, enter=None, exit=None):
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_state_gatherer.append([name, enter, exit])
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class MetaStateMachine(type):
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def __new__(cls, name, bases, dictionary):
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global _transition_gatherer, _state_gatherer
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Machine = super(MetaStateMachine, cls).__new__(cls, name, bases, dictionary)
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Machine._class_transitions = []
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Machine._class_states = {}
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for s in _state_gatherer:
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Machine._add_class_state(*s)
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for i in _transition_gatherer:
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Machine._add_class_transition(*i)
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_transition_gatherer = []
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_state_gatherer = []
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return Machine
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StateMachineBase = MetaStateMachine('StateMachineBase', (object, ), {})
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class StateMachine(StateMachineBase):
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def __init__(self):
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self._bring_definitions_to_object_level()
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self._inject_into_parts()
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self._validate_machine_definitions()
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if callable(self.initial_state):
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self.initial_state = self.initial_state()
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self._current_state_object = self._state_by_name(self.initial_state)
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self._current_state_object.run_enter(self)
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self._create_state_getters()
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def __new__(cls, *args, **kwargs):
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obj = super(StateMachine, cls).__new__(cls)
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obj._states = {}
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obj._transitions = []
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return obj
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def _bring_definitions_to_object_level(self):
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self._states.update(self.__class__._class_states)
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self._transitions.extend(self.__class__._class_transitions)
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def _inject_into_parts(self):
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for collection in [self._states.values(), self._transitions]:
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for component in collection:
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component.machine = self
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def _validate_machine_definitions(self):
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if len(self._states) < 2:
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raise InvalidConfiguration('There must be at least two states')
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if not getattr(self, 'initial_state', None):
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raise InvalidConfiguration('There must exist an initial state')
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@classmethod
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def _add_class_state(cls, name, enter, exit):
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cls._class_states[name] = _State(name, enter, exit)
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def add_state(self, name, enter=None, exit=None):
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state = _State(name, enter, exit)
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setattr(self, state.getter_name(), state.getter_method().__get__(self, self.__class__))
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self._states[name] = state
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def _current_state_name(self):
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return self._current_state_object.name
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current_state = property(_current_state_name)
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def changing_state(self, from_, to):
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"""
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This method is called whenever a state change is executed
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"""
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pass
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def _new_state(self, state):
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self.changing_state(self._current_state_object.name, state.name)
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self._current_state_object = state
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def _state_objects(self):
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return list(self._states.values())
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def states(self):
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return [s.name for s in self._state_objects()]
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@classmethod
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def _add_class_transition(cls, event, from_, to, action, guard):
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transition = _Transition(event, [cls._class_states[s] for s in _listize(from_)],
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cls._class_states[to], action, guard)
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cls._class_transitions.append(transition)
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setattr(cls, event, transition.event_method())
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def add_transition(self, event, from_, to, action=None, guard=None):
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transition = _Transition(event, [self._state_by_name(s) for s in _listize(from_)],
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self._state_by_name(to), action, guard)
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self._transitions.append(transition)
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setattr(self, event, transition.event_method().__get__(self, self.__class__))
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def _process_transitions(self, event_name, *args, **kwargs):
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transitions = self._transitions_by_name(event_name)
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transitions = self._ensure_from_validity(transitions)
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this_transition = self._check_guards(transitions)
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this_transition.run(self, *args, **kwargs)
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def _create_state_getters(self):
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for state in self._state_objects():
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setattr(self, state.getter_name(), state.getter_method().__get__(self, self.__class__))
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def _state_by_name(self, name):
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for state in self._state_objects():
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if state.name == name:
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return state
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def _transitions_by_name(self, name):
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return list(filter(lambda transition: transition.event == name, self._transitions))
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def _ensure_from_validity(self, transitions):
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valid_transitions = list(filter(
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lambda transition: transition.is_valid_from(self._current_state_object),
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transitions))
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if len(valid_transitions) == 0:
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raise InvalidTransition("Cannot %s from %s" % (
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transitions[0].event, self.current_state))
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return valid_transitions
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def _check_guards(self, transitions):
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allowed_transitions = []
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for transition in transitions:
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if transition.check_guard(self):
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allowed_transitions.append(transition)
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if len(allowed_transitions) == 0:
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raise GuardNotSatisfied("Guard is not satisfied for this transition")
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elif len(allowed_transitions) > 1:
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raise ForkedTransition("More than one transition was allowed for this event")
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return allowed_transitions[0]
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class _Transition(object):
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def __init__(self, event, from_, to, action, guard):
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self.event = event
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self.from_ = from_
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self.to = to
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self.action = action
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self.guard = _Guard(guard)
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def event_method(self):
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def generated_event(machine, *args, **kwargs):
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these_transitions = machine._process_transitions(self.event, *args, **kwargs)
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generated_event.__doc__ = 'event %s' % self.event
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generated_event.__name__ = self.event
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return generated_event
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def is_valid_from(self, from_):
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return from_ in _listize(self.from_)
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def check_guard(self, machine):
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return self.guard.check(machine)
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def run(self, machine, *args, **kwargs):
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machine._current_state_object.run_exit(machine)
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machine._new_state(self.to)
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self.to.run_enter(machine)
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_ActionRunner(machine).run(self.action, *args, **kwargs)
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class _Guard(object):
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def __init__(self, action):
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self.action = action
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def check(self, machine):
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if self.action is None:
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return True
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items = _listize(self.action)
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result = True
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for item in items:
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result = result and self._evaluate(machine, item)
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return result
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def _evaluate(self, machine, item):
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if callable(item):
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return item(machine)
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else:
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guard = getattr(machine, item)
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if callable(guard):
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guard = guard()
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return guard
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class _State(object):
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def __init__(self, name, enter, exit):
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self.name = name
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self.enter = enter
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self.exit = exit
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def getter_name(self):
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return 'is_%s' % self.name
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def getter_method(self):
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def state_getter(self_machine):
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return self_machine.current_state == self.name
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return state_getter
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def run_enter(self, machine):
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_ActionRunner(machine).run(self.enter)
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def run_exit(self, machine):
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_ActionRunner(machine).run(self.exit)
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class _ActionRunner(object):
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def __init__(self, machine):
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self.machine = machine
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def run(self, action_param, *args, **kwargs):
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if not action_param:
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return
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action_items = _listize(action_param)
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for action_item in action_items:
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self._run_action(action_item, *args, **kwargs)
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def _run_action(self, action, *args, **kwargs):
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if callable(action):
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self._try_to_run_with_args(action, self.machine, *args, **kwargs)
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else:
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self._try_to_run_with_args(getattr(self.machine, action), *args, **kwargs)
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def _try_to_run_with_args(self, action, *args, **kwargs):
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try:
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action(*args, **kwargs)
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except TypeError:
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action()
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class InvalidConfiguration(Exception):
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pass
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class InvalidTransition(Exception):
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pass
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class GuardNotSatisfied(Exception):
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pass
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class ForkedTransition(Exception):
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pass
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def _listize(value):
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return type(value) in [list, tuple] and value or [value]
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