如何使用PHP编写库存管理系统中的库存补货功能代码

class InventoryReplenishment {
    private $db; // 数据库连接对象
    
    public function __construct() {
        // 初始化数据库连接
        $this->db = new mysqli('localhost', 'username', 'password', '库存管理系统数据库');
        if ($this->db->connect_error) {
            die('数据库连接失败：' . $this->db->connect_error);
        }
    }
    
    public function replenishStock($productId, $quantity) {
        // 检查库存是否低于某个阈值，如果是，则进行库存补充操作
        $threshold = $this->getReplenishmentThreshold($productId);
        $currentStock = $this->getCurrentStock($productId);
        
        if ($currentStock < $threshold) {
            $replenishmentQuantity = $threshold - $currentStock;
            
            // 更新库存
            $sql = "UPDATE products SET stock = stock + ? WHERE id = ?";
            $stmt = $this->db->prepare($sql);
            $stmt->bind_param('ii', $replenishmentQuantity, $productId);
            $stmt->execute();
            $stmt->close();
            
            echo '产品' . $productId . '的库存已经补充至' . ($currentStock + $replenishmentQuantity);
        } else {
            echo '产品' . $productId . '的库存已经充足，无需补货';
        }
    }
    
    private function getReplenishmentThreshold($productId) {
        // 获取某个产品的库存补充阈值，可以从数据库中获取或者硬编码
        return 100; // 这里假设库存补充阈值为100
    }
    
    private function getCurrentStock($productId) {
        // 获取某个产品的当前库存，从数据库中获取
        $sql = "SELECT stock FROM products WHERE id = ?";
        $stmt = $this->db->prepare($sql);
        $stmt->bind_param('i', $productId);
        $stmt->execute();
        $stmt->bind_result($currentStock);
        $stmt->fetch();
        $stmt->close();
        
        return $currentStock;
    }
}

$inventoryReplenishment = new InventoryReplenishment();
$inventoryReplenishment->replenishStock(1, 50); // 补充产品ID为1的库存，数量为50