import datetime

from django.db import models
from django.db.models import Q


class AdManager(models.Manager):
    """ A Custom Manager for ads """

    def get_random_ad(self, ad_category, ad_zone):
        """
        Returns a random advert that belongs to the specified category and zone
        
        """
        now = datetime.datetime.now()
        if ad_category=='':
            try:
                ad = self.get_query_set().filter(
                    zone__slug=ad_zone, enabled=True).filter(
                    # is expired or no expiration
                    Q(expires_on__gt=now) | Q(expires_on__isnull=True)
                ).order_by('?')[0]
            except IndexError:
                return None
        else:
            try:
                ad = self.get_query_set().filter(
                    category__slug=ad_category, zone__slug=ad_zone,
                    enabled=True).filter(
                    # is expired or no expiration
                    Q(expires_on__gt=now) | Q(expires_on__isnull=True)
                ).order_by('?')[0]
            except IndexError:
                return None

        return ad

    def enabled(self):
        return self.get_query_set().filter(enabled=True)