federated: Log why invitations aren't offered

With -vvv, say which check stopped people from being invited to an
event: a read-only calendar, a calendar that isn't on a Core's
Nextcloud, or an event organized by someone else.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/federated/gcal-federated-core.c

@@ -221,11 +221,17 @@ gcal_federated_core_get_organizer (GcalCalendar  *calendar,
   g_return_val_if_fail (GCAL_IS_CALENDAR (calendar), FALSE);
 
   if (gcal_calendar_is_read_only (calendar))
-    return FALSE;
+    {
+      g_debug ("No invitations on %s: the calendar is read-only", gcal_calendar_get_name (calendar));
+      return FALSE;
+    }
 
   source = gcal_calendar_get_source (calendar);
   if (!source || !e_source_has_extension (source, E_SOURCE_EXTENSION_WEBDAV_BACKEND))
-    return FALSE;
+    {
+      g_debug ("No invitations on %s: not a CalDAV calendar", gcal_calendar_get_name (calendar));
+      return FALSE;
+    }
 
   webdav = e_source_get_extension (source, E_SOURCE_EXTENSION_WEBDAV_BACKEND);
   uri = e_source_webdav_dup_uri (webdav);
@@ -234,7 +240,13 @@ gcal_federated_core_get_organizer (GcalCalendar  *calendar,
   config_dir = g_build_filename (g_get_home_dir (), ".config", "coredesktop", NULL);
 
   if (!uri || !gcal_federated_core_find_core (config_dir, g_uri_get_host (uri), &core_email, &core_name))
-    return FALSE;
+    {
+      g_debug ("No invitations on %s: %s is not the Nextcloud of a Core in %s",
+               gcal_calendar_get_name (calendar),
+               uri ? g_uri_get_host (uri) : "(no address)",
+               config_dir);
+      return FALSE;
+    }
 
   /*
    * Nextcloud only sends invitations when the organizer is one of the
@@ -243,6 +255,12 @@ gcal_federated_core_get_organizer (GcalCalendar  *calendar,
    */
   server_email = e_source_webdav_dup_email_address (webdav);
 
+  g_debug ("Invitations on %s are organized by %s (server: %s, Core: %s)",
+           gcal_calendar_get_name (calendar),
+           (server_email && *server_email) ? server_email : core_email,
+           server_email ? server_email : "(none)",
+           core_email);
+
   if (out_email)
     *out_email = (server_email && *server_email) ? g_steal_pointer (&server_email) : g_steal_pointer (&core_email);
   if (out_name)

src/gui/event-editor/gcal-event-editor-dialog.c

@@ -159,6 +159,9 @@ update_invite_state (GcalEventEditorDialog *self)
         organizer_email = gcal_util_get_email_from_mailto_uri (gcal_event_organizer_get_uri (organizer));
 
       can_invite = !organizer_email || g_ascii_strcasecmp (organizer_email, email) == 0;
+
+      if (!can_invite)
+        g_debug ("No invitations: the event is organized by %s, not %s", organizer_email, email);
     }
 
   gcal_attendees_section_set_inviter (GCAL_ATTENDEES_SECTION (self->attendees_section),