Add a OfferSubscriptionQuerySet

Including summary features ; this is just a base for more work, this query-set
could be used to factorize code between CLI and JSON API.

coin/offers/models.py

@@ -4,7 +4,7 @@ from __future__ import unicode_literals
 import datetime
 
 from django.db import models
-from django.db.models import Q
+from django.db.models import Count, Q
 from django.core.validators import MinValueValidator
 
 
@@ -75,6 +75,27 @@ class Offer(models.Model):
         verbose_name = 'offre'
 
 
+class OfferSubscriptionQuerySet(models.QuerySet):
+    def running(self, at_date=None):
+        """ Only the running contracts at a given date.
+
+        Running mean already started and not stopped yet
+        """
+
+        if at_date is None:
+            at_date = datetime.date.today()
+
+        return self.filter(Q(subscription_date__lte=at_date) &
+                           (Q(resign_date__gt=at_date) |
+                            Q(resign_date__isnull=True)))
+
+    def offer_summary(self):
+        """ Agregates as a count of subscriptions per offer
+        """
+        return self.values('offer__name').annotate(
+            num_subscriptions=Count('offer'))
+
+
 class OfferSubscription(models.Model):
     """Only contains administrative details about a subscription, not
     technical.  Nothing here should end up into the LDAP backend.
@@ -103,6 +124,8 @@ class OfferSubscription(models.Model):
     member = models.ForeignKey('members.Member', verbose_name='membre')
     offer = models.ForeignKey('Offer', verbose_name='offre')
 
+    objects = OfferSubscriptionQuerySet().as_manager()
+
     def __unicode__(self):
         return '%s - %s - %s' % (self.member, self.offer.name,
                                        self.subscription_date)