diff --git a/app-backend/src/container/user.container.js b/app-backend/src/container/user.container.js
new file mode 100644
index 000000000..55b569ca8
--- /dev/null
+++ b/app-backend/src/container/user.container.js
@@ -0,0 +1,9 @@
+import UserController from '../controllers/user.controller.js';
+import UserRepository from '../repositories/user.repository.js';
+import UserService from '../services/user.service.js';
+
+const userRepository = new UserRepository();
+const userService = new UserService(userRepository);
+const userController = new UserController(userService);
+
+export default userController;
\ No newline at end of file
diff --git a/app-backend/src/controllers/user.controller.js b/app-backend/src/controllers/user.controller.js
index 11b779a94..27d76650c 100644
--- a/app-backend/src/controllers/user.controller.js
+++ b/app-backend/src/controllers/user.controller.js
@@ -1,286 +1,181 @@
-import User from '../models/User.js';
-import { ACTIONS } from "../middleware/logger.js";
-
-/**
- * @desc    View logged-in user's profile
- * @route   GET /api/v1/users/me
- * @access  Private (all roles)
- */
-export const getMyProfile = async (req, res) => {
-  const user = await User.findById(req.user.id).select('-password');
-  res.json(user);
-};
-
-/**
- * @desc    Admin: List all users
- * @route   GET /api/v1/users
- * @access  Private/Admins
- */
-export const listUsers = async (req, res) => {
-  try {
-    const users = await User.find().select('-password');
-    res.json({ total: users.length, users });
-  } catch (e) {
-    res.status(500).json({ message: e.message });
+class UserController {
+  constructor(userService) {
+    this.userService = userService;
   }
-};
-
-/**
- * @desc    Update logged-in user's profile
- * @route   PUT /api/v1/users/me
- * @access  Private (all roles)
- */
-export const updateMyProfile = async (req, res) => {
-  const fieldsToUpdate = { ...req.body };
-  delete fieldsToUpdate.role;       // prevent role changes
-  delete fieldsToUpdate.password;   // don’t allow password here
-
-  const updatedUser = await User.findByIdAndUpdate(
-    req.user.id,
-    fieldsToUpdate,
-    { new: true, runValidators: true }
-  ).select('-password');
-
-  res.json(updatedUser);
-};
-
-/**
- * @desc    Admin: View any user profile
- * @route   GET /api/v1/users/:id
- * @access  Private/Admin
- */
-export const adminGetUserProfile = async (req, res) => {
-  const user = await User.findById(req.params.id).select('-password');
-  if (!user) return res.status(404).json({ message: 'User not found' });
-  res.json(user);
-};
-
-/**
- * @desc    Admin: Update any user's profile
- * @route   PUT /api/v1/users/:id
- * @access  Private/Admin
- */
-export const adminUpdateUserProfile = async (req, res) => {
-  const fieldsToUpdate = { ...req.body };
-  delete fieldsToUpdate.password;   // separate password endpoint if needed
 
-  const updatedUser = await User.findByIdAndUpdate(
-    req.params.id,
-    fieldsToUpdate,
-    { new: true, runValidators: true }
-  ).select('-password');
-
-  if (!updatedUser) return res.status(404).json({ message: 'User not found' });
-
-  await req.audit.log(req.user.id, ACTIONS.PROFILE_UPDATED, {
-    updatedUserId: req.params.id,
-    updatedFields: Object.keys(fieldsToUpdate),
-  });
-
-  res.json(updatedUser);
-};
-
-/**
- * @desc    Get all guards (Admin + Employee only)
- * @route   GET /api/v1/users/guards
- * @access  Private/Admin,Employee
- */
-export const getAllGuards = async (req, res) => {
-  const guards = await User.find({ role: 'guard' }).select('-password');
-  res.json(guards);
-};
-
-/**
- * @desc    Admin: Delete a user
- * @route   DELETE /api/v1/users/:userId
- * @access  Private (Admin, Super Admin)
- */
-export const deleteUser = async (req, res) => {
-  try {
-    const user = await User.findByIdAndDelete(req.params.userId);
-    if (!user) {
-      return res.status(404).json({ message: 'User not found' });
+  getMyProfile = async (req, res) => {
+    try {
+      const user = await this.userService.getMyProfile(req.user.id);
+      return res.status(200).json(user);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    await req.audit?.log(req.user.id, ACTIONS.USER_DELETED, {
-      deletedUserId: req.params.userId,
-      deletedUserEmail: user.email,
-    });
-
-    return res.json({ message: 'User deleted successfully' });
-  } catch (e) {
-    return res.status(500).json({ message: e.message });
-  }
-};
-
-/**
- * @desc    Get logged-in employer's profile (Employer only)
- * @route   GET /api/v1/users/profile
- * @access  Private (Employer only)
- */
-export const getEmployerProfile = async (req, res) => {
-  try {
-    if (req.user.role !== 'employer') {
-      return res.status(403).json({ message: 'Access denied.' });
+  };
+
+  listUsers = async (req, res) => {
+    try {
+      const result = await this.userService.listUsers();
+      return res.status(200).json(result);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const employer = await User.findById(req.user.id).select('-password');
-    if (!employer) {
-      return res.status(404).json({ message: 'Employer not found' });
+  };
+
+  updateMyProfile = async (req, res) => {
+    try {
+      const updatedUser = await this.userService.updateMyProfile(
+        req.user.id,
+        req.body
+      );
+
+      return res.status(200).json(updatedUser);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    res.status(200).json(employer);
-  } catch (err) {
-    res.status(500).json({ message: err.message });
-  }
-};
-
-/**
- * @desc    Update logged-in employer's profile (Employer only)
- * @route   PUT /api/v1/users/profile
- * @access  Private (Employer only)
- */
-export const updateEmployerProfile = async (req, res) => {
-  try {
-    if (req.user.role !== 'employer') {
-      return res.status(403).json({ message: 'Access denied.' });
+  };
+
+  adminGetUserProfile = async (req, res) => {
+    try {
+      const user = await this.userService.adminGetUserProfile(req.params.userId);
+      return res.status(200).json(user);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const fieldsToUpdate = { ...req.body };
-    delete fieldsToUpdate.role;
-    delete fieldsToUpdate.password;
-
-    const updatedEmployer = await User.findByIdAndUpdate(
-      req.user.id,
-      fieldsToUpdate,
-      { new: true, runValidators: true }
-    ).select('-password');
-
-    if (!updatedEmployer) return res.status(404).json({ message: 'Employer not found' });
-    res.status(200).json(updatedEmployer);
-  } catch (err) {
-    res.status(500).json({ message: err.message });
-  }
-};
-
-/**
- * @desc    Register or update a push token for the logged-in user
- * @route   POST /api/v1/users/push-token
- * @access  Private (all roles)
- */
-export const registerPushToken = async (req, res) => {
-  try {
-    const { token, platform, deviceId } = req.body;
-
-    if (!token || typeof token !== 'string') {
-      return res.status(400).json({ message: 'Push token is required.' });
+  };
+
+  adminUpdateUserProfile = async (req, res) => {
+    try {
+      const updatedUser = await this.userService.adminUpdateUserProfile(
+        req.user.id,
+        req.params.userId,
+        req.body,
+        req.audit
+      );
+
+      return res.status(200).json(updatedUser);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const user = await User.findById(req.user.id);
-    if (!user) {
-      return res.status(404).json({ message: 'User not found' });
+  };
+
+  getAllGuards = async (req, res) => {
+    try {
+      const guards = await this.userService.getAllGuards();
+      return res.status(200).json(guards);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const existing = user.pushTokens?.find((item) => item.token === token);
-    if (existing) {
-      existing.platform = platform ?? existing.platform;
-      existing.deviceId = deviceId ?? existing.deviceId;
-      existing.updatedAt = new Date();
-    } else {
-      user.pushTokens = [
-        ...(user.pushTokens ?? []),
-        {
-          token,
-          platform,
-          deviceId,
-          updatedAt: new Date(),
-        },
-      ];
+  };
+
+  deleteUser = async (req, res) => {
+    try {
+      const result = await this.userService.deleteUser(
+        req.user.id,
+        req.params.userId,
+        req.audit
+      );
+
+      return res.status(200).json(result);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    await user.save();
-
-    return res.status(200).json({ message: 'Push token registered.' });
-  } catch (err) {
-    return res.status(500).json({ message: err.message });
-  }
-};
-/**
- * @desc    Add a guard to favourites
- * @route   POST /api/v1/users/favourites/:guardId
- * @access  Private (Employer only)
- */
-export const addFavouriteGuard = async (req, res) => {
-  try {
-    if (req.user.role !== 'employer') {
-      return res.status(403).json({ message: 'Only employers can favourite guards.' });
+  };
+
+  getEmployerProfile = async (req, res) => {
+    try {
+      const employer = await this.userService.getEmployerProfile(req.user);
+      return res.status(200).json(employer);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const { guardId } = req.params;
-
-    const guard = await User.findById(guardId);
-    if (!guard || guard.role !== 'guard') {
-      return res.status(404).json({ message: 'Guard not found' });
+  };
+
+  updateEmployerProfile = async (req, res) => {
+    try {
+      const updatedEmployer = await this.userService.updateEmployerProfile(
+        req.user,
+        req.body
+      );
+
+      return res.status(200).json(updatedEmployer);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const employer = await User.findById(req.user.id);
-
-    if (!employer.favourites.includes(guardId)) {
-      employer.favourites.push(guardId);
-      await employer.save();
+  };
+
+  registerPushToken = async (req, res) => {
+    try {
+      const result = await this.userService.registerPushToken(
+        req.user.id,
+        req.body
+      );
+
+      return res.status(200).json(result);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    res.status(200).json({ message: 'Guard added to favourites', favourites: employer.favourites });
-  } catch (err) {
-    res.status(500).json({ message: err.message });
-  }
-};
-
-
-/**
- * @desc    Remove a guard from favourites
- * @route   DELETE /api/v1/users/favourites/:guardId
- * @access  Private (Employer only)
- */
-export const removeFavouriteGuard = async (req, res) => {
-  try {
-    if (req.user.role !== 'employer') {
-      return res.status(403).json({ message: 'Only employers can modify favourites.' });
+  };
+
+  addFavouriteGuard = async (req, res) => {
+    try {
+      const result = await this.userService.addFavouriteGuard(
+        req.user,
+        req.params.guardId
+      );
+
+      return res.status(200).json(result);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
-
-    const { guardId } = req.params;
-
-    const employer = await User.findById(req.user.id);
-
-    employer.favourites = employer.favourites.filter(
-      (id) => id.toString() !== guardId
-    );
-
-    await employer.save();
-
-    res.status(200).json({ message: 'Guard removed from favourites', favourites: employer.favourites });
-  } catch (err) {
-    res.status(500).json({ message: err.message });
-  }
-};
-
-
-/**
- * @desc    Get favourite guards list
- * @route   GET /api/v1/users/favourites
- * @access  Private (Employer only)
- */
-export const getFavouriteGuards = async (req, res) => {
-  try {
-    if (req.user.role !== 'employer') {
-      return res.status(403).json({ message: 'Only employers can view favourites.' });
+  };
+
+  removeFavouriteGuard = async (req, res) => {
+    try {
+      const result = await this.userService.removeFavouriteGuard(
+        req.user,
+        req.params.guardId
+      );
+
+      return res.status(200).json(result);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
     }
+  };
+
+  getFavouriteGuards = async (req, res) => {
+    try {
+      const favourites = await this.userService.getFavouriteGuards(req.user);
+      return res.status(200).json(favourites);
+    } catch (err) {
+      return res
+        .status(err.statusCode || 500)
+        .json({ message: err.message });
+    }
+  };
+}
 
-    const employer = await User.findById(req.user.id)
-      .populate('favourites', '-password');
-
-    res.status(200).json(employer.favourites);
-  } catch (err) {
-    res.status(500).json({ message: err.message });
-  }
-};
\ No newline at end of file
+export default UserController;
\ No newline at end of file
diff --git a/app-backend/src/repositories/user.repository.js b/app-backend/src/repositories/user.repository.js
new file mode 100644
index 000000000..c26a2a853
--- /dev/null
+++ b/app-backend/src/repositories/user.repository.js
@@ -0,0 +1,40 @@
+import User from '../models/User.js';
+
+class UserRepository {
+  async findById(userId) {
+    return User.findById(userId);
+  }
+
+  async findByIdWithoutPassword(userId) {
+    return User.findById(userId).select('-password');
+  }
+
+  async findAllWithoutPassword() {
+    return User.find().select('-password');
+  }
+
+  async updateByIdWithoutPassword(userId, fieldsToUpdate) {
+    return User.findByIdAndUpdate(userId, fieldsToUpdate, {
+      new: true,
+      runValidators: true,
+    }).select('-password');
+  }
+
+  async deleteById(userId) {
+    return User.findByIdAndDelete(userId);
+  }
+
+  async findGuardsWithoutPassword() {
+    return User.find({ role: 'guard' }).select('-password');
+  }
+
+  async save(user) {
+    return user.save();
+  }
+
+  async findEmployerFavourites(userId) {
+    return User.findById(userId).populate('favourites', '-password');
+  }
+}
+
+export default UserRepository;
\ No newline at end of file
diff --git a/app-backend/src/routes/user.routes.js b/app-backend/src/routes/user.routes.js
index b3e106bf5..863bf4c0e 100644
--- a/app-backend/src/routes/user.routes.js
+++ b/app-backend/src/routes/user.routes.js
@@ -8,21 +8,7 @@ import {
   requireSameBranchAsTargetUser,
   ROLES,
 } from '../middleware/rbac.js';
-import {
-  getMyProfile,
-  updateMyProfile,
-  getEmployerProfile,
-  updateEmployerProfile,
-  adminGetUserProfile,
-  adminUpdateUserProfile,
-  getAllGuards,
-  listUsers,
-  deleteUser,
-  addFavouriteGuard,
-  removeFavouriteGuard,
-  getFavouriteGuards,
-  registerPushToken
-} from '../controllers/user.controller.js';
+import userController from '../container/user.container.js';
 
 const router = express.Router();
 
@@ -46,6 +32,8 @@ const router = express.Router();
  *         description: Successfully retrieved profile.
  *       401:
  *         description: Unauthorized
+ *       404:
+ *         description: User not found
  *   put:
  *     summary: Update logged-in user's profile
  *     tags: [Users]
@@ -64,25 +52,26 @@ const router = express.Router();
  *               email:
  *                 type: string
  *                 example: john.doe@example.com
- *               password:
+ *               phone:
  *                 type: string
- *                 example: newPassword123
- *               role:
+ *                 example: "+61400123456"
+ *               address:
  *                 type: string
- *                 enum: [user, admin]
- *                 example: user
+ *                 example: 123 Main Street
  *     responses:
  *       200:
  *         description: Successfully updated profile.
  *       401:
  *         description: Unauthorized
+ *       404:
+ *         description: User not found
  *       422:
  *         description: Validation error
  */
 router
   .route('/me')
-  .get(auth, loadUser, getMyProfile)
-  .put(auth, loadUser, updateMyProfile);
+  .get(auth, loadUser, userController.getMyProfile)
+  .put(auth, loadUser, userController.updateMyProfile);
 
 /**
  * @swagger
@@ -103,19 +92,29 @@ router
  *             properties:
  *               token:
  *                 type: string
+ *                 example: expo_push_token_here
  *               platform:
  *                 type: string
+ *                 example: android
  *               deviceId:
  *                 type: string
+ *                 example: device-123
  *     responses:
  *       200:
- *         description: Token registered
+ *         description: Push token registered successfully.
  *       400:
- *         description: Validation error
+ *         description: Push token is required.
  *       401:
  *         description: Unauthorized
+ *       404:
+ *         description: User not found
  */
-router.post('/push-token', auth, loadUser, registerPushToken);
+router.post(
+  '/push-token',
+  auth,
+  loadUser,
+  userController.registerPushToken
+);
 
 /**
  * @swagger
@@ -132,6 +131,8 @@ router.post('/push-token', auth, loadUser, registerPushToken);
  *         description: Unauthorized
  *       403:
  *         description: Forbidden (only employers)
+ *       404:
+ *         description: Employer not found
  *   put:
  *     summary: Update logged-in employer's profile
  *     tags: [Users]
@@ -146,16 +147,16 @@ router.post('/push-token', auth, loadUser, registerPushToken);
  *             properties:
  *               name:
  *                 type: string
- *                 example: "Krish Uppal"
+ *                 example: Krish Uppal
  *               email:
  *                 type: string
- *                 example: "krish@example.com"
+ *                 example: krish@example.com
  *               phone:
  *                 type: string
  *                 example: "+61400123456"
  *               address:
  *                 type: string
- *                 example: "123 Main Street"
+ *                 example: 123 Main Street
  *     responses:
  *       200:
  *         description: Successfully updated employer profile.
@@ -163,13 +164,16 @@ router.post('/push-token', auth, loadUser, registerPushToken);
  *         description: Unauthorized
  *       403:
  *         description: Forbidden
+ *       404:
+ *         description: Employer not found
  *       422:
  *         description: Validation error
  */
 router
   .route('/profile')
-  .get(auth, loadUser, getEmployerProfile)
-  .put(auth, loadUser, updateEmployerProfile);
+  .get(auth, loadUser, userController.getEmployerProfile)
+  .put(auth, loadUser, userController.updateEmployerProfile);
+
 /**
  * @swagger
  * /api/v1/users/favourites:
@@ -181,14 +185,18 @@ router
  *     responses:
  *       200:
  *         description: List of favourite guards
+ *       401:
+ *         description: Unauthorized
  *       403:
  *         description: Only employers allowed
+ *       404:
+ *         description: Employer not found
  */
 router.get(
   '/favourites',
   auth,
   loadUser,
-  getFavouriteGuards
+  userController.getFavouriteGuards
 );
 
 /**
@@ -209,16 +217,18 @@ router.get(
  *     responses:
  *       200:
  *         description: Guard added to favourites
+ *       401:
+ *         description: Unauthorized
  *       403:
  *         description: Only employers allowed
  *       404:
- *         description: Guard not found
+ *         description: Guard or employer not found
  */
 router.post(
   '/favourites/:guardId',
   auth,
   loadUser,
-  addFavouriteGuard
+  userController.addFavouriteGuard
 );
 
 /**
@@ -239,15 +249,20 @@ router.post(
  *     responses:
  *       200:
  *         description: Guard removed from favourites
+ *       401:
+ *         description: Unauthorized
  *       403:
  *         description: Only employers allowed
+ *       404:
+ *         description: Employer not found
  */
 router.delete(
   '/favourites/:guardId',
   auth,
   loadUser,
-  removeFavouriteGuard
+  userController.removeFavouriteGuard
 );
+
 /**
  * @swagger
  * /api/v1/users/guards:
@@ -270,7 +285,7 @@ router.get(
   loadUser,
   authorizeRoles(ROLES.ADMIN, ROLES.EMPLOYEE),
   authorizePermissions('user:read'),
-  getAllGuards
+  userController.getAllGuards
 );
 
 /**
@@ -295,20 +310,20 @@ router.get(
   loadUser,
   authorizeRoles(ROLES.SUPER_ADMIN, ROLES.ADMIN, ROLES.BRANCH_ADMIN),
   authorizePermissions('user:read', { any: true }),
-  listUsers
+  userController.listUsers
 );
 
 /**
  * @swagger
- * /api/v1/users/{id}:
+ * /api/v1/users/{userId}:
  *   get:
- *     summary: Admin – get another user's profile
+ *     summary: Admin get another user's profile
  *     tags: [Users]
  *     security:
  *       - bearerAuth: []
  *     parameters:
  *       - in: path
- *         name: id
+ *         name: userId
  *         schema:
  *           type: string
  *         required: true
@@ -316,20 +331,20 @@ router.get(
  *     responses:
  *       200:
  *         description: Successfully retrieved user.
- *       404:
- *         description: User not found
  *       401:
  *         description: Unauthorized
  *       403:
  *         description: Forbidden
+ *       404:
+ *         description: User not found
  *   put:
- *     summary: Admin – update another user's profile
+ *     summary: Admin update another user's profile
  *     tags: [Users]
  *     security:
  *       - bearerAuth: []
  *     parameters:
  *       - in: path
- *         name: id
+ *         name: userId
  *         required: true
  *         schema:
  *           type: string
@@ -347,22 +362,45 @@ router.get(
  *               email:
  *                 type: string
  *                 example: jane.smith@example.com
- *               password:
- *                 type: string
- *                 example: AdminUpdated123
  *               role:
  *                 type: string
- *                 enum: [user, admin]
  *                 example: admin
+ *               phone:
+ *                 type: string
+ *                 example: "+61400111222"
+ *               address:
+ *                 type: string
+ *                 example: 25 Collins Street
  *     responses:
  *       200:
  *         description: Successfully updated user.
+ *       401:
+ *         description: Unauthorized
+ *       403:
+ *         description: Forbidden
  *       404:
  *         description: User not found
+ *   delete:
+ *     summary: Admin delete a user
+ *     tags: [Users]
+ *     security:
+ *       - bearerAuth: []
+ *     parameters:
+ *       - in: path
+ *         name: userId
+ *         required: true
+ *         schema:
+ *           type: string
+ *         description: User ID
+ *     responses:
+ *       200:
+ *         description: User deleted successfully.
  *       401:
  *         description: Unauthorized
  *       403:
  *         description: Forbidden
+ *       404:
+ *         description: User not found
  */
 router
   .route('/:userId')
@@ -371,7 +409,7 @@ router
     loadUser,
     authorizeRoles(ROLES.SUPER_ADMIN, ROLES.ADMIN),
     authorizePermissions('user:read'),
-    adminGetUserProfile
+    userController.adminGetUserProfile
   )
   .put(
     auth,
@@ -379,14 +417,14 @@ router
     authorizeRoles(ROLES.SUPER_ADMIN, ROLES.ADMIN, ROLES.BRANCH_ADMIN),
     authorizePermissions('user:write'),
     requireSameBranchAsTargetUser({ paramKey: 'userId' }),
-    adminUpdateUserProfile
+    userController.adminUpdateUserProfile
   )
   .delete(
     auth,
     loadUser,
     authorizeRoles(ROLES.SUPER_ADMIN, ROLES.ADMIN),
     authorizePermissions('user:delete'),
-    deleteUser
+    userController.deleteUser
   );
 
-export default router;
+export default router;
\ No newline at end of file
diff --git a/app-backend/src/services/user.service.js b/app-backend/src/services/user.service.js
new file mode 100644
index 000000000..702ac44a1
--- /dev/null
+++ b/app-backend/src/services/user.service.js
@@ -0,0 +1,251 @@
+import { ACTIONS } from '../middleware/logger.js';
+import AppError from '../utils/AppError.js';
+
+class UserService {
+  constructor(userRepository) {
+    this.userRepository = userRepository;
+  }
+
+  sanitizeProfileUpdatePayload(payload = {}) {
+    const fieldsToUpdate = { ...payload };
+    delete fieldsToUpdate.role;
+    delete fieldsToUpdate.password;
+    return fieldsToUpdate;
+  }
+
+  sanitizeAdminProfileUpdatePayload(payload = {}) {
+    const fieldsToUpdate = { ...payload };
+    delete fieldsToUpdate.password;
+    return fieldsToUpdate;
+  }
+
+  async getMyProfile(userId) {
+    const user = await this.userRepository.findByIdWithoutPassword(userId);
+
+    if (!user) {
+      throw new AppError('User not found', 404);
+    }
+
+    return user;
+  }
+
+  async listUsers() {
+    const users = await this.userRepository.findAllWithoutPassword();
+    return {
+      total: users.length,
+      users,
+    };
+  }
+
+  async updateMyProfile(userId, payload) {
+    const fieldsToUpdate = this.sanitizeProfileUpdatePayload(payload);
+
+    const updatedUser = await this.userRepository.updateByIdWithoutPassword(
+      userId,
+      fieldsToUpdate
+    );
+
+    if (!updatedUser) {
+      throw new AppError('User not found', 404);
+    }
+
+    return updatedUser;
+  }
+
+  async adminGetUserProfile(targetUserId) {
+    const user = await this.userRepository.findByIdWithoutPassword(targetUserId);
+
+    if (!user) {
+      throw new AppError('User not found', 404);
+    }
+
+    return user;
+  }
+
+  async adminUpdateUserProfile(actorUserId, targetUserId, payload, auditLogger) {
+    const fieldsToUpdate = this.sanitizeAdminProfileUpdatePayload(payload);
+
+    const updatedUser = await this.userRepository.updateByIdWithoutPassword(
+      targetUserId,
+      fieldsToUpdate
+    );
+
+    if (!updatedUser) {
+      throw new AppError('User not found', 404);
+    }
+
+    if (auditLogger?.log) {
+      await auditLogger.log(actorUserId, ACTIONS.PROFILE_UPDATED, {
+        updatedUserId: targetUserId,
+        updatedFields: Object.keys(fieldsToUpdate),
+      });
+    }
+
+    return updatedUser;
+  }
+
+  async getAllGuards() {
+    return this.userRepository.findGuardsWithoutPassword();
+  }
+
+  async deleteUser(actorUserId, targetUserId, auditLogger) {
+    const user = await this.userRepository.deleteById(targetUserId);
+
+    if (!user) {
+      throw new AppError('User not found', 404);
+    }
+
+    if (auditLogger?.log) {
+      await auditLogger.log(actorUserId, ACTIONS.USER_DELETED, {
+        deletedUserId: targetUserId,
+        deletedUserEmail: user.email,
+      });
+    }
+
+    return { message: 'User deleted successfully' };
+  }
+
+  async getEmployerProfile(currentUser) {
+    if (currentUser.role !== 'employer') {
+      throw new AppError('Access denied.', 403);
+    }
+
+    const employer = await this.userRepository.findByIdWithoutPassword(
+      currentUser.id
+    );
+
+    if (!employer) {
+      throw new AppError('Employer not found', 404);
+    }
+
+    return employer;
+  }
+
+  async updateEmployerProfile(currentUser, payload) {
+    if (currentUser.role !== 'employer') {
+      throw new AppError('Access denied.', 403);
+    }
+
+    const fieldsToUpdate = this.sanitizeProfileUpdatePayload(payload);
+
+    const updatedEmployer = await this.userRepository.updateByIdWithoutPassword(
+      currentUser.id,
+      fieldsToUpdate
+    );
+
+    if (!updatedEmployer) {
+      throw new AppError('Employer not found', 404);
+    }
+
+    return updatedEmployer;
+  }
+
+  async registerPushToken(userId, payload) {
+    const { token, platform, deviceId } = payload;
+
+    if (!token || typeof token !== 'string') {
+      throw new AppError('Push token is required.', 400);
+    }
+
+    const user = await this.userRepository.findById(userId);
+
+    if (!user) {
+      throw new AppError('User not found', 404);
+    }
+
+    const existing = user.pushTokens?.find((item) => item.token === token);
+
+    if (existing) {
+      existing.platform = platform ?? existing.platform;
+      existing.deviceId = deviceId ?? existing.deviceId;
+      existing.updatedAt = new Date();
+    } else {
+      user.pushTokens = [
+        ...(user.pushTokens ?? []),
+        {
+          token,
+          platform,
+          deviceId,
+          updatedAt: new Date(),
+        },
+      ];
+    }
+
+    await this.userRepository.save(user);
+
+    return { message: 'Push token registered.' };
+  }
+
+  async addFavouriteGuard(currentUser, guardId) {
+    if (currentUser.role !== 'employer') {
+      throw new AppError('Only employers can favourite guards.', 403);
+    }
+
+    const guard = await this.userRepository.findById(guardId);
+
+    if (!guard || guard.role !== 'guard') {
+      throw new AppError('Guard not found', 404);
+    }
+
+    const employer = await this.userRepository.findById(currentUser.id);
+
+    if (!employer) {
+      throw new AppError('Employer not found', 404);
+    }
+
+    const alreadyExists = employer.favourites.some(
+      (id) => id.toString() === guardId
+    );
+
+    if (!alreadyExists) {
+      employer.favourites.push(guardId);
+      await this.userRepository.save(employer);
+    }
+
+    return {
+      message: 'Guard added to favourites',
+      favourites: employer.favourites,
+    };
+  }
+
+  async removeFavouriteGuard(currentUser, guardId) {
+    if (currentUser.role !== 'employer') {
+      throw new AppError('Only employers can modify favourites.', 403);
+    }
+
+    const employer = await this.userRepository.findById(currentUser.id);
+
+    if (!employer) {
+      throw new AppError('Employer not found', 404);
+    }
+
+    employer.favourites = employer.favourites.filter(
+      (id) => id.toString() !== guardId
+    );
+
+    await this.userRepository.save(employer);
+
+    return {
+      message: 'Guard removed from favourites',
+      favourites: employer.favourites,
+    };
+  }
+
+  async getFavouriteGuards(currentUser) {
+    if (currentUser.role !== 'employer') {
+      throw new AppError('Only employers can view favourites.', 403);
+    }
+
+    const employer = await this.userRepository.findEmployerFavourites(
+      currentUser.id
+    );
+
+    if (!employer) {
+      throw new AppError('Employer not found', 404);
+    }
+
+    return employer.favourites;
+  }
+}
+
+export default UserService;
\ No newline at end of file
diff --git a/app-backend/src/utils/AppError.js b/app-backend/src/utils/AppError.js
new file mode 100644
index 000000000..63e4fe095
--- /dev/null
+++ b/app-backend/src/utils/AppError.js
@@ -0,0 +1,10 @@
+class AppError extends Error {
+  constructor(message, statusCode = 500) {
+    super(message);
+    this.name = 'AppError';
+    this.statusCode = statusCode;
+    Error.captureStackTrace?.(this, this.constructor);
+  }
+}
+
+export default AppError;
\ No newline at end of file