"""
Basic building blocks for generic class based views.

We don't bind behaviour to http method handlers yet,
which allows mixin classes to be composed in interesting ways.
"""
from __future__ import unicode_literals

from django.http import Http404
from rest_framework import status
from rest_framework.response import Response


class CreateModelMixin(object):
    """
    Create a model instance.
    Should be mixed in with any `BaseView`.
    """
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.DATA, files=request.FILES)
        if serializer.is_valid():
            self.pre_save(serializer.object)
            self.object = serializer.save()
            headers = self.get_success_headers(serializer.data)
            return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def get_success_headers(self, data):
        try:
            return {'Location': data['url']}
        except (TypeError, KeyError):
            return {}

    def pre_save(self, obj):
        pass


class ListModelMixin(object):
    """
    List a queryset.
    Should be mixed in with `MultipleObjectAPIView`.
    """
    empty_error = "Empty list and '%(class_name)s.allow_empty' is False."

    def list(self, request, *args, **kwargs):
        queryset = self.get_queryset()
        self.object_list = self.filter_queryset(queryset)

        # Default is to allow empty querysets.  This can be altered by setting
        # `.allow_empty = False`, to raise 404 errors on empty querysets.
        allow_empty = self.get_allow_empty()
        if not allow_empty and not self.object_list:
            class_name = self.__class__.__name__
            error_msg = self.empty_error % {'class_name': class_name}
            raise Http404(error_msg)

        # Pagination size is set by the `.paginate_by` attribute,
        # which may be `None` to disable pagination.
        page_size = self.get_paginate_by(self.object_list)
        if page_size:
            packed = self.paginate_queryset(self.object_list, page_size)
            paginator, page, queryset, is_paginated = packed
            serializer = self.get_pagination_serializer(page)
        else:
            serializer = self.get_serializer(self.object_list)

        return Response(serializer.data)


class RetrieveModelMixin(object):
    """
    Retrieve a model instance.
    Should be mixed in with `SingleObjectBaseView`.
    """
    def retrieve(self, request, *args, **kwargs):
        self.object = self.get_object()
        serializer = self.get_serializer(self.object)
        return Response(serializer.data)


class UpdateModelMixin(object):
    """
    Update a model instance.
    Should be mixed in with `SingleObjectBaseView`.
    """
    def update(self, request, *args, **kwargs):
        try:
            self.object = self.get_object()
            created = False
        except Http404:
            self.object = None
            created = True

        serializer = self.get_serializer(self.object, data=request.DATA, files=request.FILES)

        if serializer.is_valid():
            self.pre_save(serializer.object)
            self.object = serializer.save()
            status_code = created and status.HTTP_201_CREATED or status.HTTP_200_OK
            return Response(serializer.data, status=status_code)

        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

    def pre_save(self, obj):
        """
        Set any attributes on the object that are implicit in the request.
        """
        # pk and/or slug attributes are implicit in the URL.
        pk = self.kwargs.get(self.pk_url_kwarg, None)
        if pk:
            setattr(obj, 'pk', pk)

        slug = self.kwargs.get(self.slug_url_kwarg, None)
        if slug:
            slug_field = self.get_slug_field()
            setattr(obj, slug_field, slug)


class DestroyModelMixin(object):
    """
    Destroy a model instance.
    Should be mixed in with `SingleObjectBaseView`.
    """
    def destroy(self, request, *args, **kwargs):
        self.object = self.get_object()
        self.object.delete()
        return Response(status=status.HTTP_204_NO_CONTENT)