/// <returns>returns new version</returns>
        public long SaveEvents(string id, IEnumerable<IEvent> changes, long expectedVersion)
        {
            _storageFactory.InitializeForWriting();
            ITapeStream stream = _storageFactory.GetOrCreateStream(id);

            if (expectedVersion != -1 && expectedVersion != stream.GetCurrentVersion())
            {
                throw new ConcurrencyException();
            }

            foreach (IEvent @event in changes)
            {
                if (stream.TryAppend(_serializer.Serialize(@event)))
                {
                    _publisher.SendOne(@event);
                }
            }
            return stream.GetCurrentVersion();
        }