add a bunch of stuff copied from Foxchat.NET

Foxnouns.Backend/ExpectedError.cs

@@ -0,0 +1,67 @@
+using System.Net;
+using Foxnouns.Backend.Middleware;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Newtonsoft.Json.Linq;
+
+namespace Foxnouns.Backend;
+
+public class FoxnounsError(string message, Exception? inner = null) : Exception(message)
+{
+    public Exception? Inner => inner;
+
+    public class DatabaseError(string message, Exception? inner = null) : FoxnounsError(message, inner);
+
+    public class UnknownEntityError(Type entityType, Exception? inner = null)
+        : DatabaseError($"Entity of type {entityType.Name} not found", inner);
+}
+
+public class ApiError(string message, HttpStatusCode? statusCode = null) : FoxnounsError(message)
+{
+    public readonly HttpStatusCode StatusCode = statusCode ?? HttpStatusCode.InternalServerError;
+
+    public class Unauthorized(string message) : ApiError(message, statusCode: HttpStatusCode.Unauthorized);
+
+    public class Forbidden(string message, IEnumerable<string>? scopes = null)
+        : ApiError(message, statusCode: HttpStatusCode.Forbidden)
+    {
+        public readonly string[] Scopes = scopes?.ToArray() ?? [];
+    }
+
+    public class BadRequest(string message, ModelStateDictionary? modelState = null)
+        : ApiError(message, statusCode: HttpStatusCode.BadRequest)
+    {
+        public readonly ModelStateDictionary? Errors = modelState;
+
+        public JObject ToJson()
+        {
+            var o = new JObject
+            {
+                { "status", (int)HttpStatusCode.BadRequest },
+                { "code", ErrorCode.BadRequest.ToString() }
+            };
+            if (Errors == null) return o;
+
+            var a = new JArray();
+            foreach (var error in Errors.Where(e => e.Value is { Errors.Count: > 0 }))
+            {
+                var errorObj = new JObject
+                {
+                    { "key", error.Key },
+                    {
+                        "errors",
+                        new JArray(error.Value!.Errors.Select(e => new JObject { { "message", e.ErrorMessage } }))
+                    }
+                };
+
+                a.Add(errorObj);
+            }
+
+            o.Add("errors", a);
+            return o;
+        }
+    }
+
+    public class NotFound(string message) : ApiError(message, statusCode: HttpStatusCode.NotFound);
+
+    public class AuthenticationError(string message) : ApiError(message, statusCode: HttpStatusCode.BadRequest);
+}