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from typing import Any, Callable, ClassVar, Dict, List, Optional, Set, Tuple, Type
class StateGraph:
"""
Represents a graph of possible states and transitions to attempt on them.
Does not support subclasses of existing graphs yet.
"""
states: ClassVar[Dict[str, "State"]]
choices: ClassVar[List[Tuple[object, str]]]
initial_state: ClassVar["State"]
terminal_states: ClassVar[Set["State"]]
def __init_subclass__(cls) -> None:
# Collect state memebers
cls.states = {}
for name, value in cls.__dict__.items():
if name in ["__module__", "__doc__", "states"]:
pass
elif name in ["initial_state", "terminal_states", "choices"]:
raise ValueError(f"Cannot name a state {name} - this is reserved")
elif isinstance(value, State):
value._add_to_graph(cls, name)
elif callable(value) or isinstance(value, classmethod):
pass
else:
raise ValueError(
f"Graph has item {name} of unallowed type {type(value)}"
)
# Check the graph layout
terminal_states = set()
initial_state = None
for state in cls.states.values():
# Check for multiple initial states
if state.initial:
if initial_state:
raise ValueError(
f"The graph has more than one initial state: {initial_state} and {state}"
)
initial_state = state
# Collect terminal states
if state.terminal:
state.externally_progressed = True
terminal_states.add(state)
# Ensure they do NOT have a handler
try:
state.handler
except AttributeError:
pass
else:
raise ValueError(
f"Terminal state '{state}' should not have a handler method ({state.handler_name})"
)
else:
# Ensure non-terminal/manual states have a try interval and a handler
if not state.externally_progressed:
if not state.try_interval:
raise ValueError(
f"State '{state}' has no try_interval and is not terminal or manual"
)
try:
state.handler
except AttributeError:
raise ValueError(
f"State '{state}' does not have a handler method ({state.handler_name})"
)
if initial_state is None:
raise ValueError("The graph has no initial state")
cls.initial_state = initial_state
cls.terminal_states = terminal_states
# Generate choices
cls.choices = [(name, name) for name in cls.states.keys()]
class State:
"""
Represents an individual state
"""
def __init__(
self,
try_interval: Optional[float] = None,
handler_name: Optional[str] = None,
externally_progressed: bool = False,
):
self.try_interval = try_interval
self.handler_name = handler_name
self.externally_progressed = externally_progressed
self.parents: Set["State"] = set()
self.children: Set["State"] = set()
def _add_to_graph(self, graph: Type[StateGraph], name: str):
self.graph = graph
self.name = name
self.graph.states[name] = self
if self.handler_name is None:
self.handler_name = f"handle_{self.name}"
def __repr__(self):
return f"<State {self.name}>"
def __eq__(self, other):
if isinstance(other, State):
return self is other
return self.name == other
def __hash__(self):
return hash(id(self))
def transitions_to(self, other: "State"):
self.children.add(other)
other.parents.add(other)
@property
def initial(self):
return not self.parents
@property
def terminal(self):
return not self.children
@property
def handler(self) -> Callable[[Any], Optional[str]]:
# Retrieve it by name off the graph
if self.handler_name is None:
raise AttributeError("No handler defined")
return getattr(self.graph, self.handler_name)
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