Implement ending/replacing date logic

uncloud_pay/models.py

@@ -57,6 +57,10 @@ def end_before(a_date):
     """ Return suitable datetimefield for ending just before a_date """
     return a_date - datetime.timedelta(seconds=1)
 
+def start_after(a_date):
+    """ Return suitable datetimefield for starting just after a_date """
+    return a_date + datetime.timedelta(seconds=1)
+
 def default_payment_delay():
     return timezone.now() + BILL_PAYMENT_DELAY
 
@@ -333,6 +337,24 @@ class Order(models.Model):
 
         return self.starting_date + datetime.timedelta(seconds=self.recurring_period)
 
+    @property
+    def next_ending_date(self):
+        """
+        Return the next proper ending date after n times the
+        recurring_period, where n is an integer.
+        """
+
+        if self.recurring_period > 0:
+            now = timezone.now()
+            delta = now - self.starting_date
+
+            num_times = math.ceil(delta.total_seconds() / self.recurring_period)
+
+            next_date = self.starting_date + datetime.timedelta(seconds= num_times * self.recurring_period)
+        else:
+            next_date = self.starting_date
+
+        return next_date
 
     @property
     def count_billed(self):
@@ -698,7 +720,6 @@ class Product(UncloudModel):
 
 
     def create_or_update_recurring_order(self, when_to_start=None, recurring_period=None):
-
         if not self.recurring_price:
             return
 
@@ -709,6 +730,13 @@ class Product(UncloudModel):
             when_to_start = timezone.now()
 
         if self.last_recurring_order:
+            # If the new order is less in value than the previous
+            # order, the previous order needs to be finished first
+            if self.recurring_price < self.last_recurring_order.price:
+
+                if when_to_start < self.last_recurring_order.next_ending_date:
+                    when_to_start = start_after(self.last_recurring_order.next_ending_date)
+
             when_to_end = end_before(when_to_start)
 
             new_order = Order.objects.create(owner=self.owner,