from  __future__ import absolute_import
from functools import partial

from django.db.models import Model

from .comparison import _compare_mapping, register
from . import compare as base_compare


def instance_fields(instance):
    opts = instance._meta
    for name in (
        'concrete_fields',
        'virtual_fields',
        'private_fields',
    ):
        fields = getattr(opts, name, None)
        if fields:
            for field in fields:
                yield field


def model_to_dict(instance, exclude, include_not_editable):
    data = {}
    for f in instance_fields(instance):
        if f.name in exclude:
            continue
        if not getattr(f, 'editable', False) and not include_not_editable:
            continue
        data[f.name] = f.value_from_object(instance)
    return data


def compare_model(x, y, context):
    """
    Returns an informative string describing the differences between the two
    supplied Django model instances. The way in which this comparison is
    performed can be controlled using the following parameters:

    :param ignore_fields:
      A sequence of fields to ignore during comparison, most commonly
      set to ``['id']``. By default, no fields are ignored.

    :param non_editable_fields:
      If `True`, then fields with ``editable=False`` will be included in the
      comparison. By default, these fields are ignored.
    """
    ignore_fields = context.get_option('ignore_fields', set())
    non_editable_fields= context.get_option('non_editable_fields', False)
    args = []
    for obj in x, y:
        args.append(model_to_dict(obj, ignore_fields, non_editable_fields))
    args.append(context)
    args.append(x)
    return _compare_mapping(*args)

register(Model, compare_model)


compare = partial(base_compare, ignore_eq=True)