Move some functions into a utils module

agenda/utils.py

@@ -0,0 +1,23 @@
+"""Utility functions."""
+
+import datetime
+
+DateOrDateTime = datetime.datetime | datetime.date
+
+
+def as_date(d: DateOrDateTime) -> datetime.date:
+    """Convert datetime to date."""
+    if isinstance(d, datetime.datetime):
+        return d.date()
+    assert isinstance(d, datetime.date)
+    return d
+
+
+def as_datetime(d: DateOrDateTime) -> datetime.datetime:
+    """Date/time of event."""
+    t0 = datetime.datetime.min.time()
+    return (
+        d
+        if isinstance(d, datetime.datetime)
+        else datetime.datetime.combine(d, t0).replace(tzinfo=datetime.timezone.utc)
+    )