add instance metrics to server

AMNet.Server/WebServer.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Globalization;
 using System.Text.Json;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
@@ -53,12 +54,28 @@ internal static class WebServer
         var app = builder.Build();
         
         app.UseCors();
-        app.MapGet("/amnet/info", () => Results.Ok(new SystemState(ApiVersion, Config.GameId, Config.ServerName)));
+
+        app.MapGet("/amnet/info", ServerInfo);
         app.MapPost("/amnet/signin", ProcessCard);
 
         return app;
     }
-    
+
+    private static IResult ServerInfo()
+    {
+        var startedAt = Volatile.Read(ref DllMain.ServerStartedAt);
+        var lastPollAt = Volatile.Read(ref DllMain.LastPollTime);
+
+        var state = new SystemState(
+            ApiVersion,
+            Config.GameId,
+            Config.ServerName,
+            Environment.TickCount64 - startedAt,
+            lastPollAt < 0 ? null : Environment.TickCount64 - lastPollAt);
+        
+        return Results.Ok(state);
+    }
+
     private static async Task ProcessCard(HttpContext ctx)
     {
         CardReadRequest request;