from rest_framework import serializers
from rest_framework.relations import MANY_RELATION_KWARGS


class CustomManyRelatedField(serializers.ManyRelatedField):
    def to_internal_value(self, data):
        if isinstance(data, str) or not hasattr(data, '__iter__'):
            self.fail('not_a_list', input_type=type(data).__name__)
        if not self.allow_empty and len(data) == 0:
            self.fail('empty')
        if data == ['']:
            data = []
        return [
            self.child_relation.to_internal_value(item)
            for item in data
        ]


class PrimaryKeyM2MField(serializers.PrimaryKeyRelatedField):

    @classmethod
    def many_init(cls, *args, **kwargs):
        list_kwargs = {'child_relation': cls(*args, **kwargs)}
        for key in kwargs:
            if key in MANY_RELATION_KWARGS:
                list_kwargs[key] = kwargs[key]
        return CustomManyRelatedField(**list_kwargs)

    def to_representation(self, value):
        return super().to_representation(value)