from rest_framework.serializers import HyperlinkedModelSerializer


class DynamicFieldsModelSerializer(HyperlinkedModelSerializer):
    """
    A HyperlinkedModelSerializer that takes an additional `fields` argument that
    controls which fields should be displayed.
    """

    def __init__(self, *args, **kwargs):
        # Don't pass the 'fields' arg up to the superclass
        fields = kwargs.pop("fields", None)
        exclude = kwargs.pop("exclude", None)
        # Instantiate the superclass normally
        super().__init__(*args, **kwargs)

        if fields:
            # Drop any fields that are not specified in the `fields` argument.
            allowed = set(fields)
            existing = set(self.fields.keys())
            for field_name in existing - allowed:
                self.fields.pop(field_name)
        if exclude:
            # Drop fields that are specified in the `exclude` argument.
            excluded = set(exclude)
            for field_name in excluded:
                try:
                    self.fields.pop(field_name)
                except KeyError:
                    pass
