from rest_framework import serializers



class SingleTag(str):

    def __init__(self, *args, **kwargs):
        pass

    def __str__(self):
        return self


class SingleTagSerializerField(serializers.Field):
    child = serializers.CharField()
    default_error_messages = {
        'not_a_str': 'Expected a string but got type "{input_type}".',
    }
    order_by = None

    def __init__(self, **kwargs):
        super(SingleTagSerializerField, self).__init__(**kwargs)

    def to_internal_value(self, value):
        if isinstance(value, str):
            if not value:
                value = ""

        if not isinstance(value, str):
            self.fail('not_a_str', input_type=type(value).__name__)

        return value

    def to_representation(self, value):
        if not isinstance(value, SingleTag):
            if not isinstance(value, str):
                value = value.name
            value = SingleTag(value)
        return value