Associate remote participant w/ JitsiConference (_LEFT)

The commit message of "Associate remote participant w/ JitsiConference
(_JOINED)" explains the motivation for this commit.

conference.js

             if (user.isHidden()) {
                 return;
             }
-            APP.store.dispatch(participantLeft(id, user));
+            APP.store.dispatch(participantLeft(id, room));
             logger.log('USER %s LEFT', id, user);
             APP.API.notifyUserLeft(id);
             APP.UI.removeUser(id, user.getDisplayName());

modules/UI/shared_video/SharedVideo.js

                     UIEvents.UPDATE_SHARED_VIDEO, null, 'removed');
             });
 
-        APP.store.dispatch(participantLeft(this.url));
+        APP.store.dispatch(participantLeft(this.url, APP.conference));
 
         this.url = null;
         this.isSharedVideoShown = false;

react/features/base/conference/actions.js

         })));
     conference.on(
         JitsiConferenceEvents.USER_LEFT,
-        (...args) => dispatch(participantLeft(...args)));
+        id => dispatch(participantLeft(id, conference)));
     conference.on(
         JitsiConferenceEvents.USER_ROLE_CHANGED,
         (...args) => dispatch(participantRoleChanged(...args)));

react/features/base/participants/actions.js

         const participant = getLocalParticipant(getState);
 
         if (participant) {
-            return dispatch(participantLeft(participant.id));
+            return (
+                dispatch(
+                    participantLeft(
+                        participant.id,
+
+                        // XXX Only the local participant is allowed to leave
+                        // without stating the JitsiConference instance because
+                        // the local participant is uniquely identified by the
+                        // very fact that there is only one local participant
+                        // (and the fact that the local participant "joins" at
+                        // the beginning of the app and "leaves" at the end of
+                        // the app).
+                        undefined)));
         }
     };
 }
  * Action to signal that a participant has left.
  *
  * @param {string} id - Participant's ID.
+ * @param {JitsiConference} conference - The {@code JitsiConference} associated
+ * with the participant identified by the specified {@code id}. Only the local
+ * participant is allowed to not specify an associated {@code JitsiConference}
+ * instance.
  * @returns {{
  *     type: PARTICIPANT_LEFT,
  *     participant: {
+ *         conference: JitsiConference,
  *         id: string
  *     }
  * }}
  */
-export function participantLeft(id) {
+export function participantLeft(id, conference) {
     return {
         type: PARTICIPANT_LEFT,
         participant: {
+            conference,
             id
         }
     };

react/features/base/participants/reducer.js

     case PARTICIPANT_JOINED:
         return [ ...state, _participantJoined(action) ];
 
-    case PARTICIPANT_LEFT:
-        return state.filter(p => p.id !== action.participant.id);
+    case PARTICIPANT_LEFT: {
+        // XXX A remote participant is uniquely identified by their id in a
+        // specific JitsiConference instance. The local participant is uniquely
+        // identified by the very fact that there is only one local participant
+        // (and the fact that the local participant "joins" at the beginning of
+        // the app and "leaves" at the end of the app).
+        const { conference, id } = action.participant;
+
+        return state.filter(p =>
+            !(
+                p.id === id
+                    && (p.local
+                        || (conference && p.conference === conference))));
+    }
     }
 
     return state;