Fix calculation of default time span for constant costs.

1 files changed, 10 insertions, 2 deletions

diff --git a/app/views/consts.py b/app/views/consts.py
index 4b5ea68..c8d9d99 100644
--- a/app/views/consts.py
+++ b/app/views/consts.py
@@ -13,6 +13,14 @@ from functools import partial
 mod = Blueprint('consts', __name__)
 assert_authorisation = partial(assert_authorisation, ConstExpense.get)
 
+def one_year(d):
+    """Returns the date d', such that [d, d'] spans exactly one year.
+    In effect, this is d + 11 months (NB: not 12!)"""
+    if d.month == 1:
+        return d.replace(month = 12)
+    else:
+        return d.replace(month = (d.month + 11) % 12, year = d.year + 1)
+
 #
 # Form
 #
@@ -23,7 +31,7 @@ class ConstForm(F.Form):
 
     end = F.DateField(u'Ende', F.req,
             format='%m.%Y',
-            default=lambda: today().replace(year = today().year + 1),
+            default=lambda: one_year(today()),
             description=u'(einschließlich)')
 
     months = F.IntegerField(u'Zahlungsrythmus', F.req,
@@ -155,7 +163,7 @@ def add_from(other):
     # replace some fields to be more meaningful
     start = max(form.end.data, today())
     form.start.data = start
-    form.end.data = start.replace(year = start.year + 1)
+    form.end.data = one_year(start)
     if not other.next: form.prev.data = other
 
     return { 'form': form }