refactor: normalize Author entity, eliminate magic strings, and improve exception handling per PR review

src/NexusReader.Application/DTOs/User/AuthorDto.cs

@@ -0,0 +1,7 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record AuthorDto
+{
+    public int Id { get; init; }
+    public string Name { get; init; } = string.Empty;
+}

src/NexusReader.Application/DTOs/User/UserProfileDto.cs

@@ -23,7 +23,7 @@ public record LastReadBookDto
 {
     public Guid Id { get; init; }
     public string Title { get; init; } = string.Empty;
-    public string Author { get; init; } = string.Empty;
+    public AuthorDto Author { get; init; } = new();
     public string? CoverUrl { get; init; }
     public double Progress { get; init; }
     public string? LastChapter { get; init; }

src/NexusReader.Data/Persistence/AppDbContext.cs

@@ -24,6 +24,7 @@ public class AppDbContext : IdentityDbContext<NexusUser>
     public DbSet<Ebook> Ebooks => Set<Ebook>();
     public DbSet<QuizResult> QuizResults => Set<QuizResult>();
     public DbSet<SubscriptionPlan> SubscriptionPlans => Set<SubscriptionPlan>();
+    public DbSet<Author> Authors => Set<Author>();
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -89,6 +90,11 @@ public class AppDbContext : IdentityDbContext<NexusUser>
                 .HasForeignKey(e => e.UserId)
                 .OnDelete(DeleteBehavior.Cascade);
 
+            entity.HasOne(e => e.Author)
+                .WithMany(a => a.Ebooks)
+                .HasForeignKey(e => e.AuthorId)
+                .OnDelete(DeleteBehavior.Restrict);
+            
             entity.HasIndex(e => e.TenantId);
         });
 

src/NexusReader.Domain/Entities/Author.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace NexusReader.Domain.Entities;
+
+public class Author
+{
+    [Key]
+    public int Id { get; set; }
+
+    [Required]
+    [MaxLength(255)]
+    public string Name { get; set; } = string.Empty;
+
+    public virtual ICollection<Ebook> Ebooks { get; set; } = new List<Ebook>();
+}

src/NexusReader.Domain/Entities/Ebook.cs

@@ -15,8 +15,11 @@ public class Ebook
     [MaxLength(255)]
     public string Title { get; set; } = string.Empty;
 
-    [MaxLength(255)]
+    [Required]
-    public string Author { get; set; } = "Unknown";
+    public int AuthorId { get; set; }
+
+    [ForeignKey(nameof(AuthorId))]
+    public virtual Author Author { get; set; } = null!;
 
     [Required]
     public string FilePath { get; set; } = string.Empty;

src/NexusReader.UI.Shared/Constants/PlanConstants.cs

@@ -0,0 +1,8 @@
+namespace NexusReader.UI.Shared.Constants;
+
+public static class PlanConstants
+{
+    public const string DefaultPlanName = "Free";
+    public const int DefaultTokenLimit = 1000;
+    public const string DefaultActivityLabel = "Brak aktywności";
+}

src/NexusReader.UI.Shared/Constants/StorageKeys.cs

@@ -0,0 +1,9 @@
+namespace NexusReader.UI.Shared.Constants;
+
+public static class StorageKeys
+{
+    public const string AuthToken = "nexus_auth_token";
+    public const string RefreshToken = "nexus_refresh_token";
+    public const string UserEmail = "nexus_user_email";
+    public const string UserTenant = "nexus_user_tenant";
+}

src/NexusReader.UI.Shared/Pages/Dashboard.razor

@@ -60,7 +60,7 @@
                                         <div class="progress-bubble">@(_profile.LastReadBook.Progress)%</div>
                                     </div>
                                 </div>
-                                <span class="progress-detail">Postęp: @(_profile.LastReadBook.Progress)% - @_profile.LastReadBook.Author</span>
+                                <span class="progress-detail">Postęp: @(_profile.LastReadBook.Progress)% - @_profile.LastReadBook.Author.Name</span>
                             </div>
                             <p class="reading-desc">
                                 Kontynuuj odkrywanie wiedzy w książce "@_profile.LastReadBook.Title". 

src/NexusReader.UI.Shared/Services/IdentityService.cs

@@ -2,6 +2,7 @@ using System.Net.Http.Json;
 using Microsoft.AspNetCore.Components.Authorization;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Application.DTOs.User;
+using NexusReader.UI.Shared.Constants;
 using FluentResults;
 
 namespace NexusReader.UI.Shared.Services;
@@ -25,9 +26,9 @@ public record UserProfile(
     LastReadBookDto? LastReadBook)
 {
     // Helper properties for UI compatibility
-    public string CurrentPlan => Plan?.Name ?? "Standard";
+    public string CurrentPlan => Plan?.Name ?? PlanConstants.DefaultPlanName;
-    public int AITokenLimit => Plan?.AITokenLimit ?? 1000;
+    public int AITokenLimit => Plan?.AITokenLimit ?? PlanConstants.DefaultTokenLimit;
-    public string LastReadBookTitle => LastReadBook?.Title ?? "Brak aktywności";
+    public string LastReadBookTitle => LastReadBook?.Title ?? PlanConstants.DefaultActivityLabel;
 }
 
 public class IdentityService : IIdentityService
@@ -35,8 +36,8 @@ public class IdentityService : IIdentityService
     private readonly HttpClient _httpClient;
     private readonly INativeStorageService _storageService;
     private readonly AuthenticationStateProvider? _authStateProvider;
-    private const string TokenKey = "nexus_auth_token";
+    private const string TokenKey = StorageKeys.AuthToken;
-    private const string RefreshTokenKey = "nexus_refresh_token";
+    private const string RefreshTokenKey = StorageKeys.RefreshToken;
     private Task<UserProfile?>? _profileTask;
     private UserProfile? _cachedProfile;
     private DateTime _lastFetchAttempt = DateTime.MinValue;
@@ -80,7 +81,10 @@ public class IdentityService : IIdentityService
                 {
                     result = await response.Content.ReadFromJsonAsync<LoginResponse>();
                 }
-                catch (System.Text.Json.JsonException) { }
+                catch (System.Text.Json.JsonException ex) 
+                {
+                    return Result.Fail(new Error("Błąd przetwarzania odpowiedzi serwera.").CausedBy(ex));
+                }
 
                 if (result != null && !string.IsNullOrEmpty(result.AccessToken))
                 {
@@ -98,8 +102,8 @@ public class IdentityService : IIdentityService
                 if (profileResult.IsSuccess)
                 {
                     var profile = profileResult.Value;
-                    await _storageService.SaveSecureString("nexus_user_email", profile.Email);
+                    await _storageService.SaveSecureString(StorageKeys.UserEmail, profile.Email);
-                    await _storageService.SaveSecureString("nexus_user_tenant", profile.TenantId.ToString());
+                    await _storageService.SaveSecureString(StorageKeys.UserTenant, profile.TenantId.ToString());
                     (_authStateProvider as NexusAuthenticationStateProvider)?.NotifyUserAuthentication(profile.Email, profile.TenantId.ToString());
                 }
                 else
@@ -126,8 +130,8 @@ public class IdentityService : IIdentityService
             {
                 await _storageService.SaveSecureString(TokenKey, "");
                 await _storageService.SaveSecureString(RefreshTokenKey, "");
-                await _storageService.SaveSecureString("nexus_user_email", "");
+                await _storageService.SaveSecureString(StorageKeys.UserEmail, "");
-                await _storageService.SaveSecureString("nexus_user_tenant", "");
+                await _storageService.SaveSecureString(StorageKeys.UserTenant, "");
             }
             
             if (OnStateInvalidated != null) await OnStateInvalidated.Invoke();
@@ -191,8 +195,8 @@ public class IdentityService : IIdentityService
                 if (profile != null)
                 {
                     _cachedProfile = profile;
-                    await _storageService.SaveSecureString("nexus_user_email", profile.Email);
+                    await _storageService.SaveSecureString(StorageKeys.UserEmail, profile.Email);
-                    await _storageService.SaveSecureString("nexus_user_tenant", profile.TenantId.ToString());
+                    await _storageService.SaveSecureString(StorageKeys.UserTenant, profile.TenantId.ToString());
                     (_authStateProvider as NexusAuthenticationStateProvider)?.NotifyUserAuthentication(profile.Email, profile.TenantId.ToString());
                 }
                 return profile;
@@ -240,8 +244,8 @@ public class IdentityService : IIdentityService
                     if (profileResult.IsSuccess)
                     {
                         var profile = profileResult.Value;
-                        await _storageService.SaveSecureString("nexus_user_email", profile.Email);
+                        await _storageService.SaveSecureString(StorageKeys.UserEmail, profile.Email);
-                        await _storageService.SaveSecureString("nexus_user_tenant", profile.TenantId.ToString());
+                        await _storageService.SaveSecureString(StorageKeys.UserTenant, profile.TenantId.ToString());
                         (_authStateProvider as NexusAuthenticationStateProvider)?.NotifyUserAuthentication(profile.Email, profile.TenantId.ToString());
                     }
 

src/NexusReader.UI.Shared/Services/NexusAuthenticationStateProvider.cs

@@ -2,13 +2,14 @@ using System.Security.Claims;
 using System.Text.Json;
 using Microsoft.AspNetCore.Components.Authorization;
 using NexusReader.Application.Abstractions.Services;
+using NexusReader.UI.Shared.Constants;
 
 namespace NexusReader.UI.Shared.Services;
 
 public class NexusAuthenticationStateProvider : AuthenticationStateProvider
 {
     private readonly INativeStorageService _storageService;
-    private const string TokenKey = "nexus_auth_token";
+    private const string TokenKey = StorageKeys.AuthToken;
 
     public NexusAuthenticationStateProvider(INativeStorageService storageService)
     {
@@ -35,8 +36,8 @@ public class NexusAuthenticationStateProvider : AuthenticationStateProvider
             // 1. Try Token-based auth
             if (!string.IsNullOrWhiteSpace(token))
             {
-                var emailResult = await _storageService.GetSecureString("nexus_user_email");
+                var emailResult = await _storageService.GetSecureString(StorageKeys.UserEmail);
-                var tenantIdResult = await _storageService.GetSecureString("nexus_user_tenant");
+                var tenantIdResult = await _storageService.GetSecureString(StorageKeys.UserTenant);
 
                 if (emailResult.IsSuccess && !string.IsNullOrEmpty(emailResult.Value))
                 {
@@ -46,10 +47,10 @@ public class NexusAuthenticationStateProvider : AuthenticationStateProvider
             }
 
             // 2. Try Cookie-based auth indicators
-            var storedEmailResult = await _storageService.GetSecureString("nexus_user_email");
+            var storedEmailResult = await _storageService.GetSecureString(StorageKeys.UserEmail);
             if (storedEmailResult.IsSuccess && !string.IsNullOrEmpty(storedEmailResult.Value))
             {
-                var tenantIdResult = await _storageService.GetSecureString("nexus_user_tenant");
+                var tenantIdResult = await _storageService.GetSecureString(StorageKeys.UserTenant);
                 _cachedState = CreateState(storedEmailResult.Value, tenantIdResult.IsSuccess ? tenantIdResult.Value! : "unknown", "CookieAuth");
                 return _cachedState;
             }

src/NexusReader.Web.New/Program.cs

@@ -458,7 +458,11 @@ app.MapGet("/identity/profile", async (ClaimsPrincipal user, UserManager<NexusUs
             {
                 Id = e.Id,
                 Title = e.Title,
-                Author = e.Author,
+                Author = new AuthorDto 
+                { 
+                    Id = e.Author.Id, 
+                    Name = e.Author.Name 
+                },
                 CoverUrl = e.CoverUrl,
                 Progress = 65,
                 LastChapter = "Chapter 4: Renaissance in Italy"

src/NexusReader.Web.New/Services/ServerIdentityService.cs

@@ -68,7 +68,11 @@ public class ServerIdentityService : IIdentityService
                 {
                     Id = e.Id,
                     Title = e.Title,
-                    Author = e.Author,
+                    Author = new AuthorDto 
+                    { 
+                        Id = e.Author.Id, 
+                        Name = e.Author.Name 
+                    },
                     CoverUrl = e.CoverUrl,
                     Progress = 65, // Hardcoded for now as per design requirements, will link to real segments later
                     LastChapter = "Chapter 4: Renaissance in Italy"