Decouple workflow services from HTTP result types

Endpoints/ServiceResult.cs

@@ -0,0 +1,36 @@
+using GameList.Domain;
+
+namespace GameList.Endpoints;
+
+internal enum ServiceErrorCode
+{
+    BadRequest,
+    Unauthorized,
+    NotFound,
+    Conflict
+}
+
+internal sealed record ServiceError(ServiceErrorCode Code, string Detail)
+{
+    public static ServiceError BadRequest(string detail) => new(ServiceErrorCode.BadRequest, detail);
+
+    public static ServiceError Unauthorized(string detail = "Unauthorized") => new(ServiceErrorCode.Unauthorized, detail);
+
+    public static ServiceError NotFound(string detail) => new(ServiceErrorCode.NotFound, detail);
+
+    public static ServiceError Conflict(string detail) => new(ServiceErrorCode.Conflict, detail);
+
+    public static ServiceError PhaseMismatch(Phase required, Phase current) =>
+        BadRequest($"This endpoint is available in the {required} phase. Your current phase is {current}.");
+}
+
+internal readonly record struct Unit;
+
+internal readonly record struct ServiceResult<T>(T? Value, ServiceError? Error)
+{
+    public bool IsSuccess => Error is null;
+
+    public static ServiceResult<T> Success(T value) => new(value, null);
+
+    public static ServiceResult<T> Failure(ServiceError error) => new(default, error);
+}