Sort articles by number of membership/cotisation months before saving a invoice

cotisations/views.py

@@ -75,6 +75,8 @@ def new_facture(request, user, userid):
     A bit of JS is used in the template to add articles in a fancier way.
     If everything is correct, save each one of the articles, save the
     purchase object associated and finally the newly created invoice.
+    Each article is created and save sorted by the number of month-length
+    membership or connection they offer, to solve duration ambiguities.
     """
     invoice = Facture(user=user)
     # The template needs the list of articles (for the JS part)
@@ -98,7 +100,13 @@ def new_facture(request, user, userid):
             # Building a purchase for each article sold
             purchases = []
             total_price = 0
-            for art_item in articles:
+            # We sort articles by number of months of subscription in them, to solve month + day ambiguities issues
+            sorted_articles = sorted(
+                articles,
+                key=lambda art: max(art.cleaned_data["article"].duration_membership, art.cleaned_data["article"].duration_connection),
+                reverse=True
+            )
+            for art_item in sorted_articles:
                 if art_item.cleaned_data:
                     article = art_item.cleaned_data["article"]
                     quantity = art_item.cleaned_data["quantity"]