#  Copyright (c) PARRRATE T&V 2021. All rights reserved.

from bu4.evaluation.constructs.enull import ENull
from bu4.evaluation.av.envtype import envtype
from bu4.linking.states.linkingstate import LinkingState
from bu4.parsing.codes import CODE_NULL
from bu4.parsing.constructs.linked import Linked, Parsed
from bu4.linking.states.linkingfinished import LinkingFinished
from bu4.evaluation.constructs.evaluable import Evaluable


__all__ = ('PNull',)


class LNull(Linked):
    def __init__(self):
        self.future = set()

    def link(self) -> LinkingState:
        return LinkingFinished(self)

    def evaluable(self, env: envtype) -> Evaluable:
        return ENull()

    def __str__(self):
        return '?'

    def unlink(self) -> Parsed:
        return PNull()


class PNull(Parsed):
    def link(self, promise: set[bytes]) -> Linked:
        return LNull()

    def __bytes__(self):
        return bytes([CODE_NULL])