from typing import TYPE_CHECKING
from .callbacks import BoolCallbackMeta
from .callbacks import CallbackMetaList
from .callbacks import CallbackPriority
from .event import same_event_cond_builder
from .events import Events
from .exceptions import InvalidDefinition
if TYPE_CHECKING:
from .event_data import EventData
[docs]
class Transition:
"""A transition holds reference to the source and target state.
Args:
source (State): The origin state of the transition.
target (State): The target state of the transition.
event (Optional[Union[str, List[str]]]): List of designators of events that trigger this
transition. Can be either a list of strings, or a space-separated string list of event
descriptors.
internal (bool): Is the transition internal or external? Internal transitions
don't execute the state entry/exit actions. Default ``False``.
validators (Optional[Union[str, Callable, List[Callable]]]): The validation callbacks to
be invoked before the transition is executed.
cond (Optional[Union[str, Callable, List[Callable]]]): The condition callbacks to be
invoked before the transition is executed that should evaluate to `True`.
unless (Optional[Union[str, Callable, List[Callable]]]): The condition callbacks to be
invoked if the `cond` is False before the transition is executed.
on (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
when the transition is executed.
before (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
before the transition is executed.
after (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
after the transition is executed.
"""
def __init__(
self,
source,
target,
event=None,
internal=False,
validators=None,
cond=None,
unless=None,
on=None,
before=None,
after=None,
):
self.source = source
self.target = target
self.internal = internal
if internal and source is not target:
raise InvalidDefinition("Internal transitions should be self-transitions.")
self._events = Events().add(event)
self.validators = CallbackMetaList().add(validators, priority=CallbackPriority.INLINE)
self.before = CallbackMetaList().add(before, priority=CallbackPriority.INLINE)
self.on = CallbackMetaList().add(on, priority=CallbackPriority.INLINE)
self.after = CallbackMetaList().add(after, priority=CallbackPriority.INLINE)
self.cond = (
CallbackMetaList(factory=BoolCallbackMeta)
.add(cond, priority=CallbackPriority.INLINE)
.add(unless, priority=CallbackPriority.INLINE, expected_value=False)
)
def __repr__(self):
return (
f"{type(self).__name__}({self.source!r}, {self.target!r}, event={self.event!r}, "
f"internal={self.internal!r})"
)
def _setup(self):
before = self.before.add
on = self.on.add
after = self.after.add
before("before_transition", priority=CallbackPriority.GENERIC, suppress_errors=True)
on("on_transition", priority=CallbackPriority.GENERIC, suppress_errors=True)
for event in self._events:
same_event_cond = same_event_cond_builder(event)
before(
f"before_{event}",
priority=CallbackPriority.NAMING,
suppress_errors=True,
cond=same_event_cond,
)
on(
f"on_{event}",
priority=CallbackPriority.NAMING,
suppress_errors=True,
cond=same_event_cond,
)
after(
f"after_{event}",
priority=CallbackPriority.NAMING,
suppress_errors=True,
cond=same_event_cond,
)
after(
"after_transition",
priority=CallbackPriority.AFTER,
suppress_errors=True,
)
def _add_observer(self, register):
register(self.validators)
register(self.cond)
register(self.before)
register(self.on)
register(self.after)
def _check_callbacks(self, check):
check(self.validators)
check(self.cond)
check(self.before)
check(self.on)
check(self.after)
def match(self, event):
return self._events.match(event)
@property
def event(self):
return str(self._events)
@property
def events(self):
return self._events
def add_event(self, value):
self._events.add(value)
def execute(self, event_data: "EventData"):
machine = event_data.machine
args, kwargs = event_data.args, event_data.extended_kwargs
machine._callbacks_registry[self.validators].call(*args, **kwargs)
if not machine._callbacks_registry[self.cond].all(*args, **kwargs):
return False
result = machine._activate(event_data)
event_data.result = result
return True