import json

from . import data


class DSM(object):
    """Dialogue State Machine!

       Parameters
       ----------
       json_filename : str
           Path to file under data/ that contains JSON description
           of state machine.
       world : object
           Something to allow states to introspect the game state with.
       """

    def __init__(self, name, world, json_filename, state):
        self.state = state
        self.world = world
        self.states = AttrDict()
        src = json.loads(data.load(json_filename).read())
        for state, state_src in src.iteritems():
            pseudo_path = [json_filename, state]
            self.states[state] = DsmState(state, state_src, pseudo_path)
        assert self.state in self.states, "DSM must have start state %r" % (self.state,)

    def get_state(self):
        return self.states[self.state]

    def has_text(self):
        self.poke()
        return bool(self.states[self.state].text)

    def event(self, ev):
        my_locals = {
            "state": self.states,
            "world": self.world,
            "npcs": self.world.npcs,
        }
        my_locals.update(ev.items)
        state = self.states[self.state]
        next_state = state.event(my_locals)
        if next_state is not None and next_state.name in self.states:
            self.states[self.state].leave(my_locals)
            self.state = next_state.name
            # TODO: update self.world to reflect new state?
            self.states[self.state].enter(my_locals)

    def choice(self, i):
        self.event(DsmEvent(choice=i))

    def auto_next(self):
        self.event(DsmEvent(auto_next=True))

    def poke(self):
        # poke the current state to see if it feels like making
        # a transition.
        self.event(DsmEvent(poke=True))


class AttrDict(dict):

    def __getattr__(self, name):
        if name not in self:
            raise AttributeError("No attribute %r" % (name,))
        return self[name]


class DsmEvent(object):

    def __init__(self, choice=None, auto_next=False, poke=False):
        self.items = {
            "choice": choice,
            "auto_next": auto_next,
            "poke": poke,
        }


class DsmState(object):
    """State within a DSM.
       """

    def __init__(self, name, state_src, base_path):
        self.name = name
        self.text = state_src.get("text", None)
        self.choices = []
        self.triggers = []

        choices = state_src.get("choices", [])
        for i, choice in enumerate(choices):
            pseudo_path = base_path + ["choice-%d" % i]
            self.choices.append((i, choice["text"]))
            next_state_code = choice.get("next", None)
            if next_state_code is not None:
                self.triggers.append(
                    Trigger("choice == %d" % i, next_state_code, pseudo_path))

        events = state_src.get("events", [])
        for i, event in enumerate(events):
            pseudo_path = base_path + ["event-%d" % i]
            self.triggers.append(Trigger(event["matches"], event["next"],
                                         pseudo_path))

        auto_next = state_src.get("auto_next", None)
        self.auto_next = False
        if auto_next is not None:
            self.auto_next = True
            assert not self.choices, "%s: auto_next and choices are not compatible" % ":".join(base_path)
            pseudo_path = base_path + ["auto_next"]
            self.triggers.append(Trigger("""auto_next""", auto_next, pseudo_path))

        on_entry = state_src.get("on_entry", None)
        if on_entry is not None:
            self.on_entry = compile(on_entry,
                                    "<%s>" % ":".join(base_path + ["on_entry"]),
                                    "exec")
        else:
            self.on_entry = None

        on_exit = state_src.get("on_exit", None)
        if on_exit is not None:
            self.on_exit = compile(on_exit,
                                   "<%s>" % ":".join(base_path + ["on_exit"]),
                                   "exec")
        else:
            self.on_exit = None

    def __repr__(self):
        return "<%r name=%r>" % (self.__class__.__name__, self.name)

    def event(self, my_locals):
        for trigger in self.triggers:
            next_state = trigger.fire(my_locals)
            if next_state is not None:
                return next_state

    def enter(self, my_locals):
        if self.on_entry is not None:
            exec(self.on_entry, {}, my_locals.copy())

    def leave(self, my_locals):
        if self.on_exit is not None:
            exec(self.on_exit, {}, my_locals.copy())


class Trigger(object):
    """Matches DSM events and triggers state transitions.
       """

    def __init__(self, matches_code, next_state_code, pseudo_path):
        self._matches = compile(matches_code,
                                "<%s>" % ":".join(pseudo_path + ["match"]),
                                "eval")
        self._next_state = compile(next_state_code,
                                   "<%s>" % ":".join(pseudo_path + ["next"]),
                                   "eval")

    def fire(self, my_locals):
        if eval(self._matches, {}, my_locals.copy()):
            return eval(self._next_state, {}, my_locals.copy())
        return None