ระบบตะกร้าสินค้า แบบ session ลบทีละ 1 รายการแล้วมีปัญหาครับ

//ajax delete cart item
// @index = index of array  
// @index + 1 = total product
function delete() {
    $id = $_POST['id']; //product id
    $index = array_search($id, $_SESSION['id']); //search id in session
    if (strval($index) !== "") { //found
        $_SESSION['index'] = intval($_SESSION['index']) - 1; //total product - 1
        unset($_SESSION['id'][$index]); //delete id
        unset($_SESSION['name'][$index]);  //delete name
        unset($_SESSION['price'][$index]);  //delete price
        unset($_SESSION['qty'][$index]);  //delete qty
    }
    show(); //call display function for refresh cart
}

//ajax add cart item
// @index = index of array
// @index + 1 = total product
function add() {
    $id = $_POST['id'];
    $name = $_POST['name'];
    $price = $_POST['price'];
    if (!isset($_SESSION['index'])) { // if first item
        $_SESSION['index'] = 0; 
        $_SESSION['id'][0] = $id;
        $_SESSION['name'][0] = $name;
        $_SESSION['price'][0] = $price;
        $_SESSION['qty'][0] = 1;
    } else {
        //search id
        $index = array_search($id, $_SESSION['id']); //search id in session
        //if found (increase item qty)
        if (strval($index) !== "") {
            $_SESSION['qty'][$index] = intval($_SESSION['qty'][$index]) + 1; //qty +1
        } else {
            //not found (new item)
            $_SESSION['index'] = intval($_SESSION['index']) + 1;
            $new_index = $_SESSION['index'];
            $_SESSION['id'][$new_index] = $id;
            $_SESSION['name'][$new_index] = $name;
            $_SESSION['price'][$new_index] = $price;
            $_SESSION['qty'][$new_index] = 1;
        }
    }
    show();//call display function for refresh cart
}

function AddToCart(){
  $lang = $_SESSION['LANG'];
  $code = $_GET['code'];
  $qty = $_GET['qty'];
  if(isset($_SESSION[CART]['ORDER'][$code])){
    $_SESSION[CART]['ORDER'][$code]['quantity'] = $_SESSION[CART]['ORDER'][$code]['quantity'] + $qty;
    $_SESSION[CART]['ORDER'][$code]['amount'] = $_SESSION[CART]['ORDER'][$code]['quantity'] * $_SESSION[CART]['ORDER'][$code]['net_total'];
  }else{
    $obj = new clsShopping();  
    $product = $obj->LoadProductDetail($code);
    $product['quantity'] = $qty;
    $product['pic'] = Thumbnail($product['filepic'], 47);
    $product['name'] = $product["name_$lang"];
    $product['unitprice'] = $product["price"];//check package
    $product['discount_total'] = ($product['discount'] * $product["price"] / 100);//check package
    $product['net_total'] = $product["price"] - $product['discount_total'];//check package
    $_SESSION[CART]['ORDER'][$code] = $product;
  }
  
  LoadOrder();
}


function LoadOrder(){
  $obj = new clsShopping();  
  $config = $obj->LoadConfig();
  
  $result['sum']['total'] = 0;
  $result['sum']['discount_total'] = 0;
  $result['sum']['transfer_total'] = 0;
  $result['sum']['net_total'] = 0;
  $result['cart'] = array();
  
  if(!empty($_SESSION[CART]['ORDER'])){
  
    foreach($_SESSION[CART]['ORDER'] as $i => $order){
      $order['amount'] = $order['unitprice']  * $order['quantity'];

      $result['cart'][] = $order;
      $result['sum']['discount_total'] += $order['discount_total'] * $order['quantity'];
      $result['sum']['total'] += $order['unitprice']  * $order['quantity'];
    }
  
  }

  
  $result['sum']['net_total'] = $result['sum']['total'] - $result['sum']['discount_total'];
  
  if($config['shipping_min'] > $result['sum']['net_total']){
    $result['sum']['transfer_total'] = $config['shipping_fee'];
    $result['sum']['net_total'] += $config['shipping_fee'];
  }
  
  $result['sum']['cnt'] = count($_SESSION[CART]['ORDER']);
  $result['sum']['net_total'] = ceil($result['sum']['net_total']);
  
  $_SESSION[CART]['SUM'] = $result['sum'];
  
  echo json_encode($result);  
}