from django.db.models import F
from django.db.models.functions import Coalesce


def category_ordering(prefix='', excel=False):
    field = F(prefix + 'order_cat')
    if excel:
        field = Coalesce(prefix + 'excel_order', prefix + 'order_cat')
    return (field.asc(nulls_last=True), prefix + 'name', prefix + 'pk')


def product_ordering(prefix='', excel=False):
    field = F(prefix + 'order_prd')
    if excel:
        field = Coalesce(prefix + 'excel_order', prefix + 'order_prd')
    return category_ordering(prefix + 'category__', excel) + (
        field.asc(nulls_last=True), prefix + 'name', prefix + 'pk',
    )