from typing import Mapping, Iterator

from bu4.evaluation.avcontainer import AVContainer
from bu4.evaluation.aftervalue import AfterValue, envtype, Evaluable


class LambdaEnv(Mapping):
    def __getitem__(self, k: bytes) -> AfterValue:
        if k == self.name:
            return self.container
        else:
            return self.env[k]

    def __len__(self) -> int:
        return len(self.env) + 1

    def __iter__(self) -> Iterator[AfterValue]:
        yield self.name
        yield from self.env

    def __init__(self, env: envtype, name: bytes, evaluable: Evaluable):
        self.env = env
        self.name = name
        self.container = AVContainer(evaluable).after_value