Refactor duplicated code into centralized utilities

[Copilot]

Eliminated duplicated validation, error handling, and state management patterns across backend controllers and frontend stores.

Backend

Created utilities:

• passwordUtils.js - Centralized password regex, validation message, hashing, and comparison
• errorHandler.js - Standardized HTTP error responses (400/403/404/500)

Refactored: 5 controllers, 1 model

Before:

// Duplicated in auth.controller.js and user.controller.js
const passwordRegex = /^(?=.*[A-Z])(?=.*[!@#$%^&*()_+{}\[\]:;<>,.?~\\-]).{8,16}$/;
if (!passwordRegex.test(password)) {
  return res.status(400).json({ message: "Password must be 8-16..." });
}
const salt = await bcrypt.genSalt(10);
const hashed = await bcrypt.hash(password, salt);

After:

import { validatePassword, hashPassword, PASSWORD_VALIDATION_MESSAGE } from "../utils/passwordUtils.js";
if (!validatePassword(password)) {
  return handleValidationError(res, PASSWORD_VALIDATION_MESSAGE);
}
const hashed = await hashPassword(password);

Frontend

Created storeHelpers.js:

• handleStoreError() - Extract error messages from API responses
• applyFilters() - Generic array filtering for search/filter state

Refactored: 4 Zustand stores

Replaced 15+ instances of error.response?.data?.message || 'default message' and collapsed duplicate filter logic in userStore and storeStore into single reusable function.

Stats

• 13 files changed: 3 new utilities, 10 refactored files
• 128 lines of duplicated code removed
• Fixed typos: "Inavlid" → "Invalid", "Successfuly" → "Successfully"

Original prompt

Find and refactor duplicated code

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