statemachine.py

from datetime import datetime
from functools import singledispatch


class State:
    def __init__(self, meta):
        self.meta = meta

    def has_failed(self):
        return isinstance(self, Failed)

    def has_completed(self):
        return isinstance(self, Completed)


class RuntimeMixin:
    def runtime(self):
        return self.meta["ended_at"] - self.meta["started_at"]


class Initial(State):
    pass


class Submitted(State):
    pass


class Running(State):
    pass


class Completed(State, RuntimeMixin):
    pass


class Failed(State, RuntimeMixin):
    pass


@singledispatch
def move_to(from_state):
    raise Exception("Cannot move out of state {}.".format(from_state.__class__.__name__))


@move_to.register(Initial)
def _(from_state):
    return Submitted(meta=dict(from_state.meta, submitted_at=datetime.now()))

@move_to.register(Submitted)
def _(from_state):
    return Running(meta=dict(from_state.meta, started_at=datetime.now()))

@move_to.register(Running)
def _(from_state, return_code):
    if return_code == 0:
        return Completed(meta=dict(from_state.meta, ended_at=datetime.now()))
    return Failed(meta=dict(from_state.meta, ended_at=datetime.now()))


s = Initial(meta=dict(name="foo"))
print(type(s), s.meta)
s = move_to(s)
print(type(s), s.meta)
s = move_to(s)
print(type(s), s.meta)
s = move_to(s, return_code=0)
print(type(s), s.meta)
print(s.runtime())
# s = move_to(s)
# print(type(s), s.meta)