Reverse order of min in FiniteDatetimeRange.intersection

In #187 the implementation of
FiniteDatetimeRange.intersection was optimised. This introduced a very
subtle change in behaviour. Previously when left.end was equal to
right.end then the right.end was favoured. In
#187 the implementation was
(unintentionally) changed to favour left.end.

This change reverses that, to again favour right.end.

This really shouldn't matter, but it can be signidicant when
the TZ of left and right are different. Eventually we'd like
to prevent this kind of mixed TZ behaviour (see
#192), but in the short
term it seems reasonable to make this tiny change to make things
consistent again with how they were before.

tests/test_ranges.py

@@ -13,6 +13,10 @@
 from xocto import localtime, ranges
 
 
+TZ_LONDON = zoneinfo.ZoneInfo("Europe/London")
+TZ_BERLIN = zoneinfo.ZoneInfo("Europe/Berlin")
+
+
 @composite
 def valid_integer_range(draw):
     boundaries = draw(sampled_from(ranges.RangeBoundaries))
@@ -1174,6 +1178,20 @@ def test_union_with_continuum(self):
             assert ranges._is_datetime_range(range | other)
             assert range | other == other | range == ranges.DatetimeRange.continuum()
 
+        def test_preference_on_equal_end(self):
+            r1 = ranges.FiniteDatetimeRange(
+                datetime.datetime(2020, 1, 1, tzinfo=TZ_LONDON),
+                datetime.datetime(2022, 1, 1, tzinfo=TZ_LONDON),
+            )
+            r2 = ranges.FiniteDatetimeRange(
+                datetime.datetime(2021, 1, 1, hour=1, tzinfo=TZ_BERLIN),
+                datetime.datetime(2022, 1, 1, hour=1, tzinfo=TZ_BERLIN),
+            )
+            assert r1.end == r2.end
+            union = r1 | r2
+            # r1.end was picked over r2.end.
+            assert union.start.tzinfo == union.end.tzinfo == TZ_LONDON
+
     class TestIntersection:
         def test_intersection_of_touching_ranges(self):
             range = ranges.FiniteDatetimeRange(
@@ -1237,6 +1255,20 @@ def test_intersection_with_half_finite_range(self):
                 )
             )
 
+        def test_preference_on_equal_end(self):
+            r1 = ranges.FiniteDatetimeRange(
+                datetime.datetime(2020, 1, 1, tzinfo=TZ_LONDON),
+                datetime.datetime(2022, 1, 1, tzinfo=TZ_LONDON),
+            )
+            r2 = ranges.FiniteDatetimeRange(
+                datetime.datetime(2021, 1, 1, hour=1, tzinfo=TZ_BERLIN),
+                datetime.datetime(2022, 1, 1, hour=1, tzinfo=TZ_BERLIN),
+            )
+            assert r1.end == r2.end
+            intersection = r1 & r2
+            # r2.end was picked over r1.end.
+            assert intersection.start.tzinfo == intersection.end.tzinfo == TZ_BERLIN
+
     class TestLocalize:
         def test_converts_timezone(self):
             # Create a datetime range in Sydney, which is

xocto/ranges.py

@@ -861,7 +861,7 @@ def intersection(
             if left.end <= right.start:
                 return None
             else:
-                return FiniteDatetimeRange(right.start, min(left.end, right.end))
+                return FiniteDatetimeRange(right.start, min(right.end, left.end))
 
         base_intersection = super().intersection(other)
         if base_intersection is None: