def donation_income(context, invoice):

    ''' Calculates the donation income for a given invoice.

    Returns:

        the donation income.

    '''

    tickets = inventory.Product.objects.filter(category__id=settings.TICKET_PRODUCT_CATEGORY)

    cheapest_ticket = tickets.order_by('price').first()

    ticket_rbi = nonvat_price(cheapest_ticket)

    return sum(

         for ticket in invoice.lineitem_set.filter(product__in=tickets)),

        Decimal(0)).quantize(CENTS_QUANT)

# TODO: include van/de/van der/de la/etc etc etc

@register.simple_tag

def name_split(name, split_characters=None):

    tokens = name.split()

    if split_characters is None or len(name) > split_characters:

        even_split = int((len(tokens) + 1) / 2)  # Round up.