virtual void setBufferLastSeen(UserId user, const BufferId &bufferId, const QDateTime &seenDate);
virtual QHash<BufferId, QDateTime> bufferLastSeenDates(UserId user);
virtual void setBufferLastSeen(UserId user, const BufferId &bufferId, const QDateTime &seenDate);
virtual QHash<BufferId, QDateTime> bufferLastSeenDates(UserId user);