fix: add_organizer() now accepts organizer argument and replaces existing field (closes #524)

- Accept optional organizer parameter (Principal, vCalAddress, mailto:
  string, or plain email string) matching the same input types as
  add_attendee(); falls back to current principal when omitted
- Pop any pre-existing ORGANIZER field before adding to prevent duplicates
- Add unit tests covering all input types, duplicate replacement, the
  no-arg/principal path, and the no-client error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tobixen

caldav/calendarobjectresource.py

@@ -168,18 +168,42 @@ def set_end(self, end, move_dtstart=False):
 
         i.add(self._ENDPARAM, end)
 
-    def add_organizer(self) -> None:
+    def add_organizer(self, organizer=None) -> None:
         """
-        goes via self.client, finds the principal, figures out the right attendee-format and adds an
-        organizer line to the event
+        Add (or replace) the ORGANIZER field on the calendar component.
+
+        If *organizer* is omitted the current principal is used (requires
+        ``self.client`` to be set).  The *organizer* argument accepts the
+        same types as :meth:`add_attendee`:
+
+        * A :class:`~caldav.Principal` object
+        * A :class:`icalendar.vCalAddress` object
+        * A ``"mailto:user@example.com"`` string
+        * A plain email address string (``"mailto:"`` is prepended automatically)
+
+        Any pre-existing ORGANIZER field is removed before the new one is added.
         """
-        if self.client is None:
-            raise ValueError("Unexpected value None for self.client")
+        from .collection import Principal as _Principal  ## avoid circular import
 
-        principal = self.client.principal()
-        ## TODO: remove Organizer-field, if exists
-        ## TODO: what if walk returns more than one vevent?
-        self.icalendar_component.add("organizer", principal.get_vcal_address())
+        if organizer is None:
+            if self.client is None:
+                raise ValueError("Unexpected value None for self.client")
+            organizer_obj = self.client.principal().get_vcal_address()
+        elif isinstance(organizer, _Principal):
+            organizer_obj = organizer.get_vcal_address()
+        elif isinstance(organizer, vCalAddress):
+            organizer_obj = organizer
+        elif isinstance(organizer, str):
+            if organizer.startswith("mailto:"):
+                organizer_obj = vCalAddress(organizer)
+            else:
+                organizer_obj = vCalAddress("mailto:" + organizer)
+        else:
+            raise ValueError(f"Unsupported organizer type: {type(organizer)!r}")
+
+        ievent = self.icalendar_component
+        ievent.pop("organizer", None)
+        ievent.add("organizer", organizer_obj)
 
     def split_expanded(self) -> list[Self]:
         """This was used internally for processing search results.

tests/test_caldav_unit.py

@@ -2629,3 +2629,82 @@ def test_meta_section_returns_multiple_dicts(self, tmp_path):
             "https://work.example.com/dav/",
             "https://personal.example.com/dav/",
         }
+
+
+class TestAddOrganizer:
+    """Unit tests for CalendarObjectResource.add_organizer() (issue #524)."""
+
+    _ev = """\
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Test//Test//EN
+BEGIN:VEVENT
+UID:test-add-organizer@example.com
+DTSTAMP:20240101T000000Z
+DTSTART:20240601T100000Z
+DTEND:20240601T110000Z
+SUMMARY:Test event
+END:VEVENT
+END:VCALENDAR
+"""
+
+    def _make_event(self):
+        return Event(data=self._ev)
+
+    def test_add_organizer_email_string(self):
+        """Passing a plain email string sets the ORGANIZER field."""
+        ev = self._make_event()
+        ev.add_organizer("organizer@example.com")
+        organizer = ev.icalendar_component.get("organizer")
+        assert organizer is not None
+        assert "organizer@example.com" in str(organizer)
+
+    def test_add_organizer_mailto_string(self):
+        """Passing a mailto: URI sets the ORGANIZER field."""
+        ev = self._make_event()
+        ev.add_organizer("mailto:organizer@example.com")
+        organizer = ev.icalendar_component.get("organizer")
+        assert str(organizer) == "mailto:organizer@example.com"
+
+    def test_add_organizer_vcal_address(self):
+        """Passing a vCalAddress directly sets the ORGANIZER field."""
+        from icalendar import vCalAddress
+
+        ev = self._make_event()
+        addr = vCalAddress("mailto:organizer@example.com")
+        ev.add_organizer(addr)
+        organizer = ev.icalendar_component.get("organizer")
+        assert str(organizer) == "mailto:organizer@example.com"
+
+    def test_add_organizer_replaces_existing(self):
+        """Calling add_organizer twice replaces the first value, no duplicate."""
+        ev = self._make_event()
+        ev.add_organizer("first@example.com")
+        ev.add_organizer("second@example.com")
+        comp = ev.icalendar_component
+        ## icalendar stores repeated properties as a list; ORGANIZER should be
+        ## a single value, not a list.
+        organizer = comp.get("organizer")
+        assert not isinstance(organizer, list), "ORGANIZER should not be duplicated"
+        assert "second@example.com" in str(organizer)
+
+    def test_add_organizer_no_arg_uses_principal(self):
+        """Calling add_organizer() without arguments uses the current principal."""
+        from icalendar import vCalAddress
+
+        ev = self._make_event()
+        mock_client = mock.MagicMock()
+        mock_principal = mock.MagicMock()
+        mock_principal.get_vcal_address.return_value = vCalAddress("mailto:me@example.com")
+        mock_client.principal.return_value = mock_principal
+        ev.client = mock_client
+        ev.add_organizer()
+        organizer = ev.icalendar_component.get("organizer")
+        assert str(organizer) == "mailto:me@example.com"
+
+    def test_add_organizer_no_arg_no_client_raises(self):
+        """Calling add_organizer() without arguments and no client raises ValueError."""
+        ev = self._make_event()
+        ev.client = None
+        with pytest.raises(ValueError):
+            ev.add_organizer()