# Copyright (c) 2015 Ansible, Inc.
# All Rights Reserved.

# Django
from django.db import models
from django.db.models.fields.related import SingleRelatedObjectDescriptor

__all__ = ['AutoOneToOneField']

# Based on AutoOneToOneField from django-annoying:
# https://bitbucket.org/offline/django-annoying/src/a0de8b294db3/annoying/fields.py

class AutoSingleRelatedObjectDescriptor(SingleRelatedObjectDescriptor):
    """Descriptor for access to the object from its related class."""

    def __get__(self, instance, instance_type=None):
        try:
            return super(AutoSingleRelatedObjectDescriptor,
                         self).__get__(instance, instance_type)
        except self.related.related_model.DoesNotExist:
            obj = self.related.related_model(**{self.related.field.name: instance})
            if self.related.field.rel.parent_link:
                raise NotImplementedError('not supported with polymorphic!')
                for f in instance._meta.local_fields:
                    setattr(obj, f.name, getattr(instance, f.name))
            obj.save()
            return obj

class AutoOneToOneField(models.OneToOneField):
    """OneToOneField that creates related object if it doesn't exist."""

    def contribute_to_related_class(self, cls, related):
        setattr(cls, related.get_accessor_name(),
                AutoSingleRelatedObjectDescriptor(related))