def apply(self, node: _Node, action: Action) -> Optional[State]:
"""Attempt to apply an action to the given state."""
new_state = node.state.copy()
for prop in action.preconditions:
new_state.add_fact(prop)
# Make sure new_state still respects the constraints
if not self.check_state(new_state):
return None
new_state.apply(action)
if not self.check_state(new_state):
return None
# Detect cycles
state = new_state.copy()
state.apply(action.inverse())
while node.action:
state.apply(node.action.inverse())
if new_state == state:
return None
node = node.parent
return new_state
def check_action(self, node: _Node, state: State, action: Action) -> bool:
# Find the last action before a navigation action
# TODO: Fold this behaviour into ChainingOptions.check_action()
nav_parent = node
while nav_parent.action is not None and self._is_navigation(nav_parent.action):
# HACK: Going through a door is always considered navigation unless the previous action was to open that door.
parent = nav_parent.parent
if parent.action is not None and parent.action.name == "open/d":
break
if self.backward and action.name == "close/d":
break
nav_parent = parent
if nav_parent.action is not None and not self._is_navigation(action):
if self.backward:
recent = action.inverse()
pre_navigation = recent
post_navigation = nav_parent.action.inverse()
else:
recent = node.action
pre_navigation = nav_parent.action
post_navigation = action
relevant = set(post_navigation.preconditions)
if len(recent.added & relevant) == 0 or len(pre_navigation.added & relevant) == 0:
return False
return self.options.check_action(state, action)
def remove(self, action: Action) -> Tuple[bool, Optional[Action]]:
changed = super().remove(action)
if self.empty:
return changed, None
# The last action might have impacted one of the subquests.
reverse_action = self._kb.get_reverse_action(action)
if reverse_action is not None:
changed = self.push(reverse_action)
elif self.push(action.inverse()):
# The last action did impact one of the subquests
# but there's no reverse action to recover from it.
changed = True
return changed, reverse_action
