public function add($entity, $quantity)
    {
        if ($this->itemExists($entity)) {
            $cartItemIndex = $this->items->search($this->cartItemsCheck($entity));

            return $this->incrementQuantityAt($cartItemIndex, $quantity);
        }

        $this->items->push(CartItem::createFrom($entity, $quantity));

        event(new CartItemAdded($entity));

        return $this->cartUpdates($isNewItem = true);
    }