from rest_framework.response import Response
from rest_framework import serializers
from rest_framework import generics
from rest_framework import status
from rest_framework.exceptions import PermissionDenied as RestFrameworkPermissionDenied
from django.core.exceptions import PermissionDenied as DjangoPermissionDenied

class XOSRetrieveUpdateDestroyAPIView(generics.RetrieveUpdateDestroyAPIView):

    # To handle fine-grained field permissions, we have to check can_update
    # the object has been updated but before it has been saved.

    def update(self, request, *args, **kwargs):
        partial = kwargs.pop('partial', False)
        self.object = self.get_object_or_none()

        if self.object is None:
            raise Exception("Use the List API for creating objects")

        serializer = self.get_serializer(self.object, data=request.DATA,
                                         files=request.FILES, partial=partial)

        assert(serializer.object is not None)

        serializer.object.caller = request.user

        if not serializer.is_valid():
            response = {"error": "validation",
                        "specific_error": "not serializer.is_valid()",
                        "reasons": serializer.errors}
            return Response(response, status=status.HTTP_400_BAD_REQUEST)

        try:
            self.pre_save(serializer.object)
        except ValidationError as err:
            # full_clean on model instance may be called in pre_save,
            # so we have to handle eventual errors.
            response = {"error": "validation",
                         "specific_error": "ValidationError in pre_save",
                         "reasons": err.message_dict}
            return Response(response, status=status.HTTP_400_BAD_REQUEST)

        if not serializer.object.can_update(request.user):
            return Response(status=status.HTTP_400_BAD_REQUEST)

        self.object = serializer.save(force_update=True)
        self.post_save(self.object, created=False)
        return Response(serializer.data, status=status.HTTP_200_OK)

    def destroy(self, request, *args, **kwargs):
        obj = self.get_object()
        obj.caller = request.user
        if obj.can_update(request.user):
            # this is the guts of DestroyModelMixin, copied here so that we
            # can use the obj with caller set in it,
            self.pre_delete(obj)
            obj.delete()
            self.post_delete(obj)
            return Response(status=status.HTTP_204_NO_CONTENT)
        else:
            return Response(status=status.HTTP_400_BAD_REQUEST)

    def handle_exception(self, exc):
        # REST API drops the string attached to Django's PermissionDenied
        # exception, and replaces it with a generic "Permission Denied"
        if isinstance(exc, DjangoPermissionDenied):
            response=Response({'detail': str(exc)}, status=status.HTTP_403_FORBIDDEN)
            response.exception=True
            return response
        else:
            return super(XOSRetrieveUpdateDestroyAPIView, self).handle_exception(exc)

class XOSListCreateAPIView(generics.ListCreateAPIView):
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.DATA, files=request.FILES)
        if not (serializer.is_valid()):
            response = {"error": "validation",
                        "specific_error": "not serializer.is_valid()",
                        "reasons": serializer.errors}
            return Response(response, status=status.HTTP_400_BAD_REQUEST)

        # now do XOS can_update permission checking

        obj = serializer.object
        obj.caller = request.user
        if not obj.can_update(request.user):
            response = {"error": "validation",
                        "specific_error": "failed can_update",
                        "reasons": []}
            return Response(response, status=status.HTTP_400_BAD_REQUEST)

        # stuff below is from generics.ListCreateAPIView

        if (hasattr(self, "pre_save")):
            # rest_framework 2.x
            self.pre_save(serializer.object)
            self.object = serializer.save(force_insert=True)
            self.post_save(self.object, created=True)
        else:
            # rest_framework 3.x
            self.perform_create(serializer)

        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED,
                        headers=headers)

    def handle_exception(self, exc):
        # REST API drops the string attached to Django's PermissionDenied
        # exception, and replaces it with a generic "Permission Denied"
        if isinstance(exc, DjangoPermissionDenied):
            response=Response({'detail': str(exc)}, status=status.HTTP_403_FORBIDDEN)
            response.exception=True
            return response
        else:
            return super(XOSListCreateAPIView, self).handle_exception(exc)