public class EhrServerSystemDiscoveryService : IEhrSystemDiscoveryService
    {
        private EHRServerInfo _selectedServer;

        public void Probe(CancellationToken cancelToken, Action<IEnumerable<EHRServerInfo>> onEndpointDiscovered)
        {
            var explorer = new DiscoveryClient(new UdpDiscoveryEndpoint());

            var task = new Task(() =>
            {
                while (!cancelToken.IsCancellationRequested)
                {
                    var authEndpoints = explorer.Find(new FindCriteria(typeof(IAuthenticationService))
                    {
                        MaxResults = 10,
                        Duration = TimeSpan.FromMilliseconds(500)
                    }).Endpoints;

                    var initEndpoints = explorer.Find(new FindCriteria(typeof(IEhrInitializationService))
                    {
                        MaxResults = 10,
                        Duration = TimeSpan.FromMilliseconds(500)
                    }).Endpoints;

                    onEndpointDiscovered(authEndpoints.Concat(initEndpoints).Select(metadata => EHRServerInfo.Create(metadata)));
                }
            }, cancelToken);

            task.ContinueWith(t => explorer.Close());
            task.Start();
        }

        public void Select(EHRServerInfo info)
        {
            _selectedServer = info;
        }

        public bool CanSearch
        {
            get { return true; }
        }


        public bool InitializationRequired
        {
            get
            {
                return _selectedServer != null && !_selectedServer.IsInitialized;
            }
        }

        public IEhrInitializationService CreateInitializationService()
        {
            if (!InitializationRequired)
                throw new InvalidOperationException();

            return new WcfEhrInitializationServiceClient(_selectedServer.Address);
        }

        public IUserAuthenticator CreateUserAuthenticator()
        {
            if (_selectedServer == null)
                throw new InvalidOperationException("Server is not selected");

            if (InitializationRequired)
                throw new InvalidOperationException("Server is not initialized");

            return new WcfAuthenticationServiceClient(_selectedServer.Address);
        }
    }