refactored responses

ParadoxSaveParser.WebAPI/HttpHelpers/RequestHelper.cs

@@ -0,0 +1,17 @@
+using System.Linq;
+using System.Net;
+
+namespace ParadoxSaveParser.WebAPI.HttpHelpers;
+
+public class RequestHelper
+{
+    internal static ValueOrError<string> GetQueryValue(HttpListenerContext ctx, string paramName)
+    {
+        string[]? values = ctx.Request.QueryString.GetValues(paramName);
+        string? value = values?.FirstOrDefault();
+        if (string.IsNullOrEmpty(value))
+            return new ErrorMessage(HttpStatusCode.BadRequest,
+                $"No request parameter '{paramName}' provided");
+        return value;
+    }
+}