class Message(models.Model):
    text = models.TextField()
    parent_message = models.ForeignKey('self')
    parent_message.null = True
    parent_message.blank = True

class MessageForm(ModelForm):
    class Meta:
        model = Message
        fields = ['text']

class NewThreadView(generic.CreateView):
    model = Message
    fields = ['parent_message', 'text']
    success_url = reverse_lazy('main_page')

class NewReplyView(generic.CreateView):
    model = Message
    fields = ['parent_message', 'text']

    def get_success_url(self):
        return reverse_lazy('thread', kwargs={'thread_id': self.kwargs['thread_id']})