Two things:

* User views its devices, from a /manage index link
* Yavsc.Server resurection

Yavsc.Server/Helpers/BillingHelpers.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using Yavsc.Abstract.FileSystem;
+using Yavsc.Billing;
+using Yavsc.Models.Billing;
+using Yavsc.Services;
+
+namespace Yavsc.Helpers
+{
+    public static class BillingHelpers
+    {
+        public static decimal Addition(this List<IBillItem> items) => items.Aggregate<IBillItem, decimal>(0m, (t, l) => t + l.Count * l.UnitaryCost);
+
+         public static decimal Addition(this List<CommandLine> items) => items.Select(i=>((IBillItem)i)).ToList().Addition();
+
+         public static string GetBillText(this IBillable query) {
+            string total = query.GetBillItems().Addition().ToString("C", CultureInfo.CurrentUICulture);
+            string bill = string.Join("\n", query.GetBillItems().Select(l=> $"{l.Name} {l.Description} : {l.UnitaryCost} € " + ((l.Count != 1) ? "*"+l.Count.ToString() : ""))) +
+                $"\n\nTotal: {total}";
+            return bill;
+         }
+
+         public static FileInfo GetBillInfo(this IBillable bill, IBillingService service)
+         {
+             var suffix = bill.GetIsAcquitted() ? "-ack":null;
+             var filename = bill.GetFileBaseName(service)+".pdf";
+            return new FileInfo(Path.Combine(AbstractFileSystemHelpers.UserBillsDirName, filename));
+         }
+    }
+}

Yavsc.Server/Helpers/SimpleJsonPostMethod.cs

@@ -0,0 +1,99 @@
+//
+//  PostJson.cs
+//
+//  Author:
+//       Paul Schneider <paulschneider@free.fr>
+//
+//  Copyright (c) 2015 Paul Schneider
+//
+//  This program is free software: you can redistribute it and/or modify
+//  it under the terms of the GNU Lesser General Public License as published by
+//  the Free Software Foundation, either version 3 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU Lesser General Public License for more details.
+//
+//  You should have received a copy of the GNU Lesser General Public License
+//  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+using System.Net;
+using System.IO;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+using System;
+using System.Json;
+
+namespace Yavsc.Server.Helpers
+{
+    /// <summary>
+    /// Simple json post method.
+    /// </summary>
+    public class SimpleJsonPostMethod : IDisposable
+	{
+    private HttpWebRequest request=null;
+
+		/// <summary>
+		/// Initializes a new instance of the Yavsc.Helpers.SimpleJsonPostMethod class.
+		/// </summary>
+		/// <param name="pathToMethod">Path to method.</param>
+		public SimpleJsonPostMethod (string pathToMethod, string authorizationHeader = null, string method = "POST")
+		{
+			request = (HttpWebRequest) WebRequest.Create (pathToMethod);
+			request.Method = method;
+			request.Accept = "application/json";
+			request.ContentType = "application/json";
+			request.SendChunked = true;
+			request.TransferEncoding = "UTF-8";
+            if (authorizationHeader!=null)
+                request.Headers["Authorization"]=authorizationHeader;
+		}
+
+        public void Dispose()
+        {
+            request.Abort();
+        }
+
+        /// <summary>
+        /// Invoke the specified query.
+        /// </summary>
+        /// <param name="query">Query.</param>
+        public async Task<TAnswer> Invoke<TAnswer>(object query)
+		{
+
+			using (Stream streamQuery = await request.GetRequestStreamAsync()) {
+				using (StreamWriter writer = new StreamWriter(streamQuery)) {
+					writer.Write (JsonConvert.SerializeObject(query));
+				}}
+			TAnswer ans = default (TAnswer);
+			using (WebResponse response = await request.GetResponseAsync ()) {
+				using (Stream responseStream =  response.GetResponseStream ()) {
+					using (StreamReader rdr = new StreamReader (responseStream)) {
+						ans = (TAnswer) JsonConvert.DeserializeObject<TAnswer> (rdr.ReadToEnd ());
+					}
+				}
+				response.Close();
+			}
+			return ans;
+		}
+
+		public async Task<JsonValue> InvokeJson(object query)
+		{
+            JsonValue jsonDoc=null;
+			using (Stream streamQuery = request.GetRequestStream()) {
+				using (StreamWriter writer = new StreamWriter(streamQuery)) {
+					writer.Write (JsonConvert.SerializeObject(query));
+				}}
+			using (WebResponse response = request.GetResponse ()) {
+				using (Stream stream = response.GetResponseStream ()) {
+                    if (stream.Length>0)
+		      jsonDoc = await Task.Run (() => JsonObject.Load (stream));			
+				}
+				response.Close();
+			}
+			return jsonDoc;
+		}
+	}
+}
+