Rocket.Chat/app/livechat/server/hooks/saveLastVisitorMessageTs.js

import { callbacks } from '../../../callbacks';
import { LivechatRooms } from '../../../models';

callbacks.add('afterSaveMessage', function(message, room) {
	if (!(typeof room.t !== 'undefined' && room.t === 'l' && room.v && room.v.token)) {
		return message;
	}
	if (message.token) {
		LivechatRooms.setVisitorLastMessageTimestampByRoomId(room._id, message.ts);
	}
	return message;
}, callbacks.priority.HIGH, 'save-last-visitor-message-timestamp');