Index: iknow-api/Services/Implementations/UserService.cs
===================================================================
--- iknow-api/Services/Implementations/UserService.cs	(revision 28592255f5866211ebd76ae2286b6373daa6b937)
+++ iknow-api/Services/Implementations/UserService.cs	(revision d025ba3ea156ecec18d37f6bd7da78a8ecb858e1)
@@ -1,3 +1,6 @@
-using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using iknow_api.Core.Models;
+using iknow_api.Repository.Interfaces;
+// ...existing code...
 
 namespace iknow_api.Core.Services
@@ -5,12 +8,26 @@
     public class UserService
     {
-        private readonly AppDbContext _context;
+        private readonly IUserRepository _users;
 
-        public UserService(AppDbContext context)
+        public UserService(IUserRepository users)
         {
-            _context = context;
+            _users = users;
         }
 
+        public async Task<User> AddUserAsync(User user, CancellationToken cancellationToken = default)
+        {
+            if (user == null) throw new ArgumentNullException(nameof(user));
 
+            if (!string.IsNullOrWhiteSpace(user.Email))
+            {
+                user.Email = user.Email.Trim();
+
+                var exists = await _users.EmailExistsAsync(user.Email, cancellationToken);
+                if (exists)
+                    throw new InvalidOperationException("A user with this email already exists.");
+            }
+
+            return await _users.AddUserAsync(user, cancellationToken);
+        }
     }
 }
Index: iknow-api/Services/Interfaces/IUserService.cs
===================================================================
--- iknow-api/Services/Interfaces/IUserService.cs	(revision 28592255f5866211ebd76ae2286b6373daa6b937)
+++ iknow-api/Services/Interfaces/IUserService.cs	(revision d025ba3ea156ecec18d37f6bd7da78a8ecb858e1)
@@ -1,2 +1,5 @@
+using System.Threading;
+using System.Threading.Tasks;
+using iknow_api.Core.Models;
 
 namespace iknow_api.Core.Interfaces
@@ -4,5 +7,6 @@
     public interface IUserService
     {
-        Task<JsonContent> AddUser(JsonContent newUser);
+        Task<User> AddUserAsync(User user, CancellationToken cancellationToken = default);
+        Task<int> GetUserByIdAsync(int id, CancellationToken cancellationToken = default);
     }
 }