"""
Serializer fields that deal with relationships with nested resources.

These fields allow you to specify the style that should be used to represent
model relationships with hyperlinks.
"""
from __future__ import unicode_literals
from functools import reduce  # import reduce from functools for compatibility with python 3

import rest_framework.relations


# fix for basestring
try:
    basestring
except NameError:
    basestring = str


class NestedHyperlinkedRelatedField(rest_framework.relations.HyperlinkedRelatedField):
    lookup_field = 'pk'
    parent_lookup_kwargs = {
        'parent_pk': 'parent__pk'
    }

    def __init__(self, *args, **kwargs):
        self.parent_lookup_kwargs = kwargs.pop('parent_lookup_kwargs', self.parent_lookup_kwargs)
        super(NestedHyperlinkedRelatedField, self).__init__(*args, **kwargs)

    def get_url(self, obj, view_name, request, format):
        """
        Given an object, return the URL that hyperlinks to the object.

        May raise a `NoReverseMatch` if the `view_name` and `lookup_field`
        attributes are not configured to correctly match the URL conf.
        """
        # Unsaved objects will not yet have a valid URL.
        if hasattr(obj, 'pk') and obj.pk in (None, ''):
            return None

        # default lookup from rest_framework.relations.HyperlinkedRelatedField
        lookup_value = getattr(obj, self.lookup_field)
        kwargs = {self.lookup_url_kwarg: lookup_value}

        # multi-level lookup
        for parent_lookup_kwarg in list(self.parent_lookup_kwargs.keys()):
            underscored_lookup = self.parent_lookup_kwargs[parent_lookup_kwarg]

            # split each lookup by their __, e.g. "parent__pk" will be split into "parent" and "pk", or
            # "parent__super__pk" would be split into "parent", "super" and "pk"
            lookups = underscored_lookup.split('__')

            # use the Django ORM to lookup this value, e.g., obj.parent.pk
            lookup_value = reduce(getattr, [obj] + lookups)

            # store the lookup_name and value in kwargs, which is later passed to the reverse method
            kwargs.update({parent_lookup_kwarg: lookup_value})

        return self.reverse(view_name, kwargs=kwargs, request=request, format=format)

    def get_object(self, view_name, view_args, view_kwargs):
        """
        Return the object corresponding to a matched URL.

        Takes the matched URL conf arguments, and should return an
        object instance, or raise an `ObjectDoesNotExist` exception.
        """

        # default lookup from rest_framework.relations.HyperlinkedRelatedField
        lookup_value = view_kwargs[self.lookup_url_kwarg]
        kwargs = {self.lookup_url_kwarg: lookup_value}

        # multi-level lookup
        for parent_lookup_kwarg in list(self.parent_lookup_kwargs.keys()):
            lookup_value = view_kwargs[parent_lookup_kwarg]
            kwargs.update({self.parent_lookup_kwargs[parent_lookup_kwarg]: lookup_value})

        return self.get_queryset().get(**kwargs)

    def use_pk_only_optimization(self):
        return False


class NestedHyperlinkedIdentityField(NestedHyperlinkedRelatedField):
    def __init__(self, view_name=None, **kwargs):
        assert view_name is not None, 'The `view_name` argument is required.'
        kwargs['read_only'] = True
        kwargs['source'] = '*'
        super(NestedHyperlinkedIdentityField, self).__init__(view_name=view_name, **kwargs)