from marshmallow import fields
from typing import Any


NO_VALUE = "___NO_VALUE"


class NullToFieldMixin:
    """Marshmallow allow_none=True does not work inside a container:
    f = List(Int(allow_none=True)) rises for value=[1,2,null].

    So there is a mixin for custom fields classes to be used inside container:
    f = List(IntOrNull(allow_none=True, null_as=None)) returns [1,2,None] for value=[1,2,null].
    """

    def __init__(self, *args, null_to: Any = NO_VALUE, **kwargs):
        self.null_to = null_to
        super().__init__(*args, **kwargs)

    def _deserialize(self, value, attr, data, **kwargs):
        if self.null_to != NO_VALUE and value == "null":
            return self.null_to
        return super()._deserialize(value, attr, data, **kwargs)


class IntOrNull(NullToFieldMixin, fields.Int):
    pass