from django.contrib.contenttypes.models import ContentType
from django.newforms.models import BaseModelFormSet, modelformset_factory, save_instance
from django.contrib.admin.options import InlineModelAdmin, flatten_fieldsets
from django.db.models import ForeignKey
  
class GenericInlineFormset(BaseModelFormSet):
    """A formset for child objects related to a parent."""
    def __init__(self, data=None, files=None, instance=None, save_as_new=False):
        self.save_as_new = save_as_new
        self.instance = instance
        self.rel_name = '-'.join( ( self.model._meta.app_label, self.model._meta.object_name.lower(), self.ct.name,  self.obj_id.name ) )
        super(GenericInlineFormset, self).__init__(queryset=self.get_queryset(), data=data, files=files, prefix=self.rel_name)
  
    def get_queryset(self):
        if self.instance is None:
            return []
        return self.model._default_manager.filter( **{ 
                self.ct.name : ContentType.objects.get_for_model(self.instance),
                self.obj_id.name : self.instance.pk 
            })
  
    def save_new(self, form, commit=True):
        kwargs = {
            self.ct.get_attname(): ContentType.objects.get_for_model(self.instance).pk,
            self.obj_id.get_attname(): self.instance.pk,
        }
        new_obj = self.model(**kwargs)
        return save_instance(form, new_obj, commit=commit)
  
class GenericInlineModelAdmin(InlineModelAdmin):
    ct_field_name = None
    id_field_name = None
    formset = GenericInlineFormset
    can_delete = True
    can_order = True

    def get_formset( self, request, obj=None ):
        if self.declared_fieldsets:
            fields = flatten_fieldsets(self.declared_fieldsets)
        else:
            fields = None
  
        opts = self.model._meta
        ct = opts.get_field(self.ct_field_name)
        if not isinstance(ct, ForeignKey) or ct.rel.to != ContentType:
            raise Exception("fk_name '%s' is not a ForeignKey to ContentType" % (self.ct_field_name))
        obj_id = opts.get_field(self.id_field_name) # let the exception propagate
  
        FormSet = modelformset_factory(self.model, 
                                        form=self.form,
                                        formfield_callback=self.formfield_for_dbfield,
                                        formset=self.formset,
                                        extra=self.extra, 
                                        fields=fields, 
                                        can_delete=self.can_delete, 
                                        can_order=self.can_order,
                                        exclude=[ct.name, obj_id.name] )
        FormSet.ct = ct
        FormSet.obj_id = obj_id     
        return FormSet 

class GenericStackedInline(GenericInlineModelAdmin):
    template = 'admin/edit_inline/stacked.html'
 
class GenericTabularInline(GenericInlineModelAdmin):
    template = 'admin/edit_inline/tabular.html'