public void Handle(Leave cmd)
{
online.Remove(cmd.User);
var hasJoinedBefore = members.Remove(cmd.User);
if (hasJoinedBefore)
Send(cmd.User, string.Format("{1} left the room {0}!", Id, cmd.User));
}
Task On(Leave x) => Send(x.Room, $"{Id} left the room {x.Room}!");
Task On(Leave x) => Send(x.Room, $"{Id} left the room {x.Room}!");