Refactor communication models

We now use `django-notifications` and `django-contrib-comments` to manage notifications and comments.

Subscriptions are managed through the `SubscriptionMixin` model, and can correspond to unique
users and to group-like subscriptions.

communication/models.py

@@ -1,60 +1,47 @@
 from django.db import models
-from django.contrib.auth.models import User
+from django.conf import settings
+from django.contrib.auth.models import Group
+from django.contrib.auth import get_user_model
+from django.contrib.contenttypes.fields import (
+    GenericForeignKey, GenericRelation
+)
+from django.contrib.contenttypes.models import ContentType
 from django.utils.translation import ugettext_lazy as _
 
+User = get_user_model()
 
-class Notifying(models.Model):
-    subscribed = models.ManyToManyField(
-        User,
-        verbose_name=_("abonnés"),
-        related_name="subscribed_to"
+
+class Subscription(models.Model):
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveIntegerField()
+    content_object = GenericForeignKey('content_type', 'object_id')
+
+
+class UserSubscription(Subscription):
+    user = models.ForeignKey(settings.AUTH_USER_MODEL)
+    is_unsub = models.BooleanField(
+        _("désinscription"),
+        default=False
     )
 
-    def get_url(self, *args, **kwargs):
-        pass
+
+class GroupSubscription(Subscription):
+    group = models.ForeignKey(Group)
 
 
-class Notification(models.Model):
-    sent_by = models.ForeignKey(
-        Notifying,
-        related_name="notifs_sent"
-    )
-    about = models.ForeignKey(
-        Notifying,
-        related_name="notifs",
-    )
-    to = models.ForeignKey(
-        User,
-        verbose_name=_("envoyée à")
-    )
-    viewed_at = models.DateTimeField(
-        _("Vue à"),
-        blank=True
-    )
-    text = models.TextField(_("corps de la notification"))
+class SubscriptionMixin(models.Model):
+    subscribed_users = GenericRelation(UserSubscription)
+    subscribed_groups = GenericRelation(GroupSubscription)
 
+    def get_unique_users(self):
+        return self.subscribed_users.filter(is_unsub=False)
 
-class Commentable(Notifying):
-    pass
+    def get_group_users(self):
+        return User.objects.filter(group__in=self.subscribed_groups.all())
 
+    def get_all_subscribers(self):
+        return (self.get_unique_users().union(self.get_group_users())
+                    .exclude(is_unsub=True))
 
-class Thread(models.Model):
-    topic = models.OneToOneField(Commentable)
-
-
-class Comment(models.Model):
-    thread = models.ForeignKey(Thread)
-    parent = models.ForeignKey(
-        'Comment',
-        related_name="replies",
-    )
-    author = models.ForeignKey(
-        User,
-        verbose_name=_("auteur"),
-        editable=False
-    )
-    at = models.DateTimeField(
-        _("date d'écriture"),
-        auto_now_add=True
-    )
-    text = models.TextField(_("corps du message"))
+    class Meta:
+        abstract = True