add the stats endpoint

dotnet/SafelyYou/Program.cs

@@ -69,8 +69,24 @@ app.MapPost("/devices/{deviceId}/stats", (string deviceId, UploadStatsRequest re
     return Results.NoContent();
     
     // not sure where the 500 would go here beyond doing a try/catch
-}); 
+});
 
+app.MapGet("/devices/{deviceId}/stats", (string deviceId, KnownDevices knownDevices, HeartBeatHistories histories, UploadTimes uploadTimes) =>
+{
+    var device = new DeviceId(deviceId);
+    if (!knownDevices.Contains(device))
+    {
+        return Results.NotFound(new NotFoundResponse($"Device ID {deviceId} not found"));
+    }
+
+    var averageUploadTimeNanos = uploadTimes.AverageUploadTimeNanoseconds(device);
+    var timeSpanText = TimeSpan.FromTicks((long)(averageUploadTimeNanos / 100)).ToString(@"m\ms\s"); // loses accuracy on the Go nanos for this text conversion
+    var uptime = histories.Uptime(device);
+    
+    return Results.Ok(new GetDeviceStatsResponse(timeSpanText, uptime));
+    
+    // no 500 here
+});
 
 
 app.Run();

dotnet/SafelyYou/UploadTimes.cs

@@ -16,4 +16,10 @@ public sealed class UploadTimes
 
         _uploadHistories[deviceId] = (history.TotalUploadTime + uploadTimeNanos, history.UploadCounts + 1);
     }
+
+    public BigInteger AverageUploadTimeNanoseconds(DeviceId deviceId)
+    {
+        if (!_uploadHistories.TryGetValue(deviceId, out var history)) return BigInteger.Zero;
+        return history.TotalUploadTime / history.UploadCounts;
+    }
 }