add instance metrics to server

AMNet.Server/CardPresenter.cs

@@ -7,7 +7,7 @@ namespace AMNet.Server;
 /// <summary>
 /// Represents a storage location to load/read cards from
 /// </summary>
-public class CardPresenter
+internal class CardPresenter
 {
     private readonly object _cardLock = new();
     private StoredCard _currentCard;

AMNet.Server/DllMain.cs

@@ -1,3 +1,4 @@
+using System;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -13,6 +14,10 @@ public static class DllMain
 {
     private const string WebAddress = "http://card.ppc.moe";
 
+    // instance metrics
+    internal static long LastPollTime = -1;
+    internal static long ServerStartedAt;
+
     static DllMain()
     {
         PInvoke.AllocConsole();
@@ -38,6 +43,7 @@ public static class DllMain
             cancellationRegistration?.Dispose();
         });
 
+        Volatile.Write(ref ServerStartedAt, Environment.TickCount64);
         App.RunAsync();
         return 0;
     }
@@ -45,6 +51,8 @@ public static class DllMain
     [UnmanagedCallersOnly(EntryPoint = "aime_io_nfc_poll")]
     public static int NfcPoll(byte unitNo)
     {
+        Volatile.Write(ref LastPollTime, Environment.TickCount64);
+
         if (!Config.EnableAimeTxt)
         {
             return 1;

AMNet.Server/SerializerContext.cs

@@ -5,7 +5,9 @@ namespace AMNet.Server;
 public record SystemState(
     [property: JsonPropertyName("apiVersion")] int ApiVersion,
     [property: JsonPropertyName("gameId")] string GameId,
-    [property: JsonPropertyName("serverName")] string ServerName);
+    [property: JsonPropertyName("serverName")] string ServerName,
+    [property: JsonPropertyName("sessionUptime")] long SessionUptime,
+    [property: JsonPropertyName("timeSinceLastPoll")] long? TimeSinceLastPoll);
 
 public record CardReadRequest(
     [property: JsonPropertyName("cardId")] string MatrixCode);

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;