add UserRendererService and improve errors

Foxnouns.Backend/Services/UserRendererService.cs

@@ -0,0 +1,36 @@
+using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
+using Microsoft.EntityFrameworkCore;
+using Newtonsoft.Json;
+
+namespace Foxnouns.Backend.Services;
+
+public class UserRendererService(DatabaseContext db, MemberRendererService memberRendererService)
+{
+    public async Task<object> RenderUserAsync(User user, User? selfUser = null, bool renderMembers = true)
+    {
+        renderMembers = renderMembers && (!user.ListHidden || selfUser?.Id == user.Id);
+
+        var members = renderMembers ? await db.Members.Where(m => m.UserId == user.Id).ToListAsync() : [];
+
+        return new UserResponse(
+            user.Id, user.Username, user.DisplayName, user.Bio, user.MemberTitle, user.Avatar, user.Links, user.Names,
+            user.Pronouns, user.Fields,
+            renderMembers ? members.Select(memberRendererService.RenderPartialMember) : null);
+    }
+
+    public record UserResponse(
+        Snowflake Id,
+        string Username,
+        string? DisplayName,
+        string? Bio,
+        string? MemberTitle,
+        string? AvatarUrl,
+        string[] Links,
+        IEnumerable<FieldEntry> Names,
+        IEnumerable<Pronoun> Pronouns,
+        IEnumerable<Field> Fields,
+        [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
+        IEnumerable<MemberRendererService.PartialMember>? Members
+    );
+}