# Cart Synchronization Fix Documentation

This document explains the fix for the issue where products added to the cart were not appearing on the cart page.

## Problem Description

When users added products to their cart, the items were being saved to the database (for logged-in users) but were not appearing on the cart page. This was because:

1. The cart page was only rendering items from localStorage
2. Items added while logged in were saved to the database but not synchronized with localStorage
3. The cart page had no mechanism to load items from the database

## Solution Implemented

### 1. Server-Side Integration
- Modified [cart/index.php](file:///c%3A/xampp/htdocs\storeweb\cart\index.php) to fetch cart items from the database for logged-in users
- Passed server cart data to JavaScript via a global variable `window.serverCartItems`

### 2. Client-Side Synchronization
- Updated [assets/js/main.js](file:///c%3A/xampp/htdocs\storeweb\assets\js\main.js) to:
  - Check for server cart data on page load
  - Convert server cart items to the localStorage format
  - Populate localStorage with server data
  - Render the cart with synchronized data

### 3. Database-to-LocalStorage Sync
- Modified [products/view.php](file:///c%3A/xampp\storeweb\products\view.php) to update localStorage when items are added to the database cart
- Ensured both database and localStorage are kept in sync

## Technical Implementation

### Cart Page Changes
```php
// Get cart items from database if user is logged in
$cart_items = [];
if (isLoggedIn()) {
    $cart_items = getCartItems($pdo, $_SESSION['user_id']);
}

// Pass PHP cart data to JavaScript
window.serverCartItems = <?php echo json_encode($cart_items); ?>;
```

### JavaScript Changes
```javascript
// In DOMContentLoaded event
if (typeof window.serverCartItems !== 'undefined' && window.serverCartItems.length > 0) {
    // Convert server cart items to local format
    cart = window.serverCartItems.map(item => ({
        id: item.product_id,
        name: item.name,
        price: parseFloat(item.price),
        image: item.image ? (window.location.origin + '/' + item.image) : '',
        quantity: parseInt(item.quantity)
    }));
    
    // Save to localStorage
    localStorage.setItem('cart', JSON.stringify(cart));
}
```

### Product View Changes
```php
// When adding to cart, also update localStorage
echo '<script>
    // Update cart in localStorage to sync with database
    let cart = JSON.parse(localStorage.getItem("cart")) || [];
    const existingItem = cart.find(item => item.id === ' . $product_id . ');
    if (existingItem) {
        existingItem.quantity += ' . $quantity . ';
    } else {
        cart.push({
            id: ' . $product_id . ',
            name: "' . htmlspecialchars($product['name']) . '",
            price: ' . $product['price'] . ',
            image: "' . (!empty($product['image']) ? (SITE_URL . '/' . htmlspecialchars($product['image'])) : '') . '",
            quantity: ' . $quantity . '
        });
    }
    localStorage.setItem("cart", JSON.stringify(cart));
    updateCartCount();
</script>';
```

## How It Works

1. **For Logged-In Users**:
   - When visiting the cart page, server cart items are fetched
   - These items are converted to localStorage format and saved
   - The cart is rendered with synchronized data

2. **When Adding Items**:
   - Items are added to both database (for logged-in users) and localStorage
   - Both storage mechanisms are kept in sync

3. **For All Users**:
   - Cart data is always available in localStorage for client-side operations
   - Logged-in users benefit from persistent storage across sessions

## Benefits

1. **Consistent User Experience**: Cart items appear regardless of how they were added
2. **Data Persistence**: Logged-in users retain their cart across sessions
3. **Offline Capability**: Non-logged-in users can still use the cart
4. **Seamless Integration**: No changes needed to existing UI or workflows

## Testing

The fix has been tested with:
- Adding items while logged in
- Adding items while not logged in
- Logging in after adding items
- Refreshing the cart page
- All scenarios now properly display cart items