public function insert($tableName, array $data)
    {
        $query = sprintf("INSERT INTO $tableName (%s) VALUES (%s)",
            implode(', ', array_keys($data)), 
            implode(', ', array_fill(0, count($data), '?'))
        );

        $stmt = $this->prepare($query);
        $stmt->execute(array_values($data));
        return $stmt;
    }