from django.core.urlresolvers import reverse
from django.db import router
from django.db.models.deletion import Collector
from django.core.exceptions import PermissionDenied
from django.views import generic

from .mixins import MessageUserMixin


class DeleteModelView(MessageUserMixin, generic.DeleteView):
    """View for deleting an object and all linked by foreign key data."""

    viewset = None

    def has_object_permission(self, request, obj):
        """Object delete permission check.

        If view had a `viewset`, the `viewset.has_delete_permission` used.
        """
        if self.viewset is not None:
            return self.viewset.has_delete_permission(request, obj)
        raise NotImplementedError('Viewset is not provided')

    def _get_deleted_objects(self):
        collector = Collector(using=router.db_for_write(self.object))
        collector.collect([self.object])
        return collector.data

    def get_context_data(self, **kwargs):
        """Extend view context data.

        `{{ deleted_objects }}` - list of related objects to delete
        """
        kwargs.setdefault('deleted_objects', self._get_deleted_objects())
        return super(DeleteModelView, self).get_context_data(**kwargs)

    def get_object(self):
        """Retrive the object for delete.

        Check object delete permission at the same time.
        """
        obj = super(DeleteModelView, self).get_object()
        if not self.has_object_permission(self.request, obj):
            raise PermissionDenied
        return obj

    def get_success_url(self):
        """Redirect back to the list view if no `success_url` is configured."""
        if self.success_url is None:
            opts = self.model._meta
            return reverse('{}:{}_list'.format(opts.app_label, opts.model_name))
        return super(DeleteModelView, self).get_success_url()

    def get_template_names(self):
        """
        List of templates for the view.

        If no `self.template_name` defined, uses::

             [<app_label>/<model_label>_delete.html,
              'material/frontend/views/confirm_delete.html']
        """
        if self.template_name is None:
            opts = self.model._meta
            return [
                '{}/{}{}.html'.format(opts.app_label, opts.model_name, self.template_name_suffix),
                'material/frontend/views/confirm_delete.html',
            ]

        return [self.template_name]

    def delete(self, request, *args, **kwargs):
        response = super(DeleteModelView, self).delete(request, *args, **kwargs)
        self.message_user()
        return response

    def message_user(self):
        self.success('The {name} "{link}"  was deleted successfully.')