"""
Generic views that provide commonly needed behaviour.
"""
from __future__ import unicode_literals
from rest_framework import views, mixins
from rest_framework.settings import api_settings
from django.views.generic.detail import SingleObjectMixin
from django.views.generic.list import MultipleObjectMixin


### Base classes for the generic views ###

class GenericAPIView(views.APIView):
    """
    Base class for all other generic views.
    """

    model = None
    serializer_class = None
    model_serializer_class = api_settings.DEFAULT_MODEL_SERIALIZER_CLASS
    filter_backend = api_settings.FILTER_BACKEND

    def filter_queryset(self, queryset):
        """
        Given a queryset, filter it with whichever filter backend is in use.
        """
        if not self.filter_backend:
            return queryset
        backend = self.filter_backend()
        return backend.filter_queryset(self.request, queryset, self)

    def get_serializer_context(self):
        """
        Extra context provided to the serializer class.
        """
        return {
            'request': self.request,
            'format': self.format_kwarg,
            'view': self
        }

    def get_serializer_class(self):
        """
        Return the class to use for the serializer.

        Defaults to using `self.serializer_class`, falls back to constructing a
        model serializer class using `self.model_serializer_class`, with
        `self.model` as the model.
        """
        serializer_class = self.serializer_class

        if serializer_class is None:
            class DefaultSerializer(self.model_serializer_class):
                class Meta:
                    model = self.model
            serializer_class = DefaultSerializer

        return serializer_class

    def get_serializer(self, instance=None, data=None,
                       files=None, many=False, partial=False):
        """
        Return the serializer instance that should be used for validating and
        deserializing input, and for serializing output.
        """
        serializer_class = self.get_serializer_class()
        context = self.get_serializer_context()
        return serializer_class(instance, data=data, files=files,
                                many=many, partial=partial, context=context)

    def pre_save(self, obj):
        """
        Placeholder method for calling before saving an object.
        May be used eg. to set attributes on the object that are implicit
        in either the request, or the url.
        """
        pass

    def post_save(self, obj, created=False):
        """
        Placeholder method for calling after saving an object.
        """
        pass


class MultipleObjectAPIView(MultipleObjectMixin, GenericAPIView):
    """
    Base class for generic views onto a queryset.
    """

    paginate_by = api_settings.PAGINATE_BY
    paginate_by_param = api_settings.PAGINATE_BY_PARAM
    pagination_serializer_class = api_settings.DEFAULT_PAGINATION_SERIALIZER_CLASS

    def get_pagination_serializer(self, page=None):
        """
        Return a serializer instance to use with paginated data.
        """
        class SerializerClass(self.pagination_serializer_class):
            class Meta:
                object_serializer_class = self.get_serializer_class()

        pagination_serializer_class = SerializerClass
        context = self.get_serializer_context()
        return pagination_serializer_class(instance=page, context=context)

    def get_paginate_by(self, queryset):
        """
        Return the size of pages to use with pagination.
        """
        if self.paginate_by_param:
            query_params = self.request.QUERY_PARAMS
            try:
                return int(query_params[self.paginate_by_param])
            except (KeyError, ValueError):
                pass
        return self.paginate_by


class SingleObjectAPIView(SingleObjectMixin, GenericAPIView):
    """
    Base class for generic views onto a model instance.
    """

    pk_url_kwarg = 'pk'  # Not provided in Django 1.3
    slug_url_kwarg = 'slug'  # Not provided in Django 1.3
    slug_field = 'slug'

    def get_object(self, queryset=None):
        """
        Override default to add support for object-level permissions.
        """
        obj = super(SingleObjectAPIView, self).get_object(queryset)
        self.check_object_permissions(self.request, obj)
        return obj


### Concrete view classes that provide method handlers ###
### by composing the mixin classes with a base view.   ###


class CreateAPIView(mixins.CreateModelMixin,
                    GenericAPIView):

    """
    Concrete view for creating a model instance.
    """
    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)


class ListAPIView(mixins.ListModelMixin,
                  MultipleObjectAPIView):
    """
    Concrete view for listing a queryset.
    """
    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)


class RetrieveAPIView(mixins.RetrieveModelMixin,
                      SingleObjectAPIView):
    """
    Concrete view for retrieving a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)


class DestroyAPIView(mixins.DestroyModelMixin,
                     SingleObjectAPIView):

    """
    Concrete view for deleting a model instance.
    """
    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)


class UpdateAPIView(mixins.UpdateModelMixin,
                    SingleObjectAPIView):

    """
    Concrete view for updating a model instance.
    """
    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def patch(self, request, *args, **kwargs):
        return self.partial_update(request, *args, **kwargs)


class ListCreateAPIView(mixins.ListModelMixin,
                        mixins.CreateModelMixin,
                        MultipleObjectAPIView):
    """
    Concrete view for listing a queryset or creating a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.list(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        return self.create(request, *args, **kwargs)


class RetrieveUpdateAPIView(mixins.RetrieveModelMixin,
                            mixins.UpdateModelMixin,
                            SingleObjectAPIView):
    """
    Concrete view for retrieving, updating a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def patch(self, request, *args, **kwargs):
        return self.partial_update(request, *args, **kwargs)


class RetrieveDestroyAPIView(mixins.RetrieveModelMixin,
                             mixins.DestroyModelMixin,
                             SingleObjectAPIView):
    """
    Concrete view for retrieving or deleting a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)


class RetrieveUpdateDestroyAPIView(mixins.RetrieveModelMixin,
                                   mixins.UpdateModelMixin,
                                   mixins.DestroyModelMixin,
                                   SingleObjectAPIView):
    """
    Concrete view for retrieving, updating or deleting a model instance.
    """
    def get(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    def put(self, request, *args, **kwargs):
        return self.update(request, *args, **kwargs)

    def patch(self, request, *args, **kwargs):
        return self.partial_update(request, *args, **kwargs)

    def delete(self, request, *args, **kwargs):
        return self.destroy(request, *args, **kwargs)