fix(events): a meeting moved to a new host is sent with the attendees as given (PPT-2640)

spec/controllers/events_spec.cr

@@ -1846,10 +1846,11 @@ describe Events, tags: ["event"] do
 
       cancelled.size.should eq 1
       resent.size.should eq 1
-      # the room is invited by the new meeting, and the old host stays involved
+      # the room is invited by the new meeting, and the previous host is not,
+      # as the attendees sent no longer list them
       invited = JSON.parse(resent.first)["attendees"].as_a.map { |attendee| attendee["emailAddress"]["address"].as_s.downcase }
       invited.should contain "room1@example.com"
-      invited.should contain organiser
+      invited.should_not contain organiser
 
       # the meeting keeps its identity in PlaceOS: same metadata record, so
       # visitors, check-in state and extension data survive the move
@@ -1865,6 +1866,29 @@ describe Events, tags: ["event"] do
       payload["previous_host_email"].as_s.should eq organiser
     end
 
+    it "keeps the previous host in the moved meeting when the attendees sent still list them" do
+      event_id, _, _, _ = create_event.call(true)
+      new_host = "another-host@example.com"
+      EventsHelper.stub_calendar_write_access(new_host)
+      WebMock.stub(:delete, "https://graph.microsoft.com/v1.0/users/dev%40acaprojects.onmicrosoft.com/calendar/events/#{URI.encode_path_segment(event_id)}")
+        .to_return(status: 204, body: "")
+      resent = [] of String
+      WebMock.stub(:post, "https://graph.microsoft.com/v1.0/users/#{URI.encode_path_segment(new_host)}/calendar/events")
+        .to_return do |request|
+          resent << (request.body.try(&.gets_to_end) || "")
+          HTTP::Client::Response.new(201, body: EventsHelper.mock_event_id("evt-moved-with-old-host", "ical-moved-002", recurring: false, organizer: new_host).to_json)
+        end
+
+      resp = client.patch("#{EVENTS_BASE}/#{event_id}?system_id=#{system_id}", headers: headers,
+        body: EventsHelper.reassign_host_input(host: new_host, extra_attendee: organiser))
+      resp.status_code.should eq(200)
+
+      resent.size.should eq 1
+      invited = JSON.parse(resent.first)["attendees"].as_a.map { |attendee| attendee["emailAddress"]["address"].as_s.downcase }
+      invited.should contain organiser
+      invited.should contain new_host
+    end
+
     it "supersedes a reassignment when the meeting moves to the new host" do
       event_id, changed_bodies, _, _ = create_event.call(true)
 

src/controllers/events.cr

@@ -635,18 +635,20 @@ class Events < Application
     update_attendees = !changes.attendees.nil?
     attendees = changes.attendees.try(&.map { |a| a.email.downcase }) || existing_attendees
 
-    # Ensure the host is configured to be attending the meeting and has accepted the meeting
-    unless host.in?(attendees)
+    # Handing the meeting to someone else means moving it to their calendar,
+    # which Office365 only allows by cancelling and re-sending it (PPT-2375).
+    new_organiser = requested_organiser(changes, organiser: host, requester: user_email)
+
+    # Ensure the host is configured to be attending the meeting and has accepted the meeting.
+    # A meeting moving to a new host is sent with the attendees as given, so the
+    # previous host is only invited when the request still lists them.
+    unless new_organiser || host.in?(attendees)
       host_attendee = PlaceCalendar::Event::Attendee.new(name: host, email: host, response_status: "accepted")
       host_attendee.visit_expected = true
       changes.attendees << host_attendee
       attendees << host
     end
 
-    # Handing the meeting to someone else means moving it to their calendar,
-    # which Office365 only allows by cancelling and re-sending it (PPT-2375).
-    new_organiser = requested_organiser(changes, organiser: host, requester: user_email)
-
     # Naming a host without moving the meeting is recorded against the event
     # metadata instead, for deployments where the organiser is a room or a
     # service account rather than a person. A transfer supersedes it: the new