implement automatic creation of mailbox names

- create mailbox name when saving new mailboxes in admin
- add MailboxManager that implement get_next_mailbox_name as manager for
  Mailbox

gnuviechadmin/managemails/models.py

@@ -20,12 +20,32 @@ class ActivateAbleMixin(models.Model):
         abstract = True
 
 
+class MailboxManager(models.Manager):
+
+    def get_next_mailbox_name(self, osuser):
+        count = 1
+        mailboxformat = "{0}p{1:02d}"
+        mailboxname = mailboxformat.format(osuser.username, count)
+
+        for box in self.values('username').filter(osuser=osuser).order_by(
+            'username'
+        ):
+            if box['username'] == mailboxname:
+                count += 1
+                mailboxname = mailboxformat.format(osuser.username, count)
+            else:
+                break
+        return mailboxname
+
+
 @python_2_unicode_compatible
 class Mailbox(ActivateAbleMixin, TimeStampedModel, models.Model):
     osuser = models.ForeignKey(OsUser)
     username = models.CharField(max_length=128, unique=True)
     password = models.CharField(max_length=255)
 
+    objects = MailboxManager()
+
     class Meta:
         verbose_name = _('Mailbox')
         verbose_name_plural = _('Mailboxes')