<?php
namespace core\db;

use PDO;
use PDOException;

/**
 * 数据库操作类
 */
class Db
{
    private static $pdo = null;

    public static function pdo()
    {
        if (self::$pdo !== null) {
            return self::$pdo;
        }

        try {
            $dsn    = sprintf('mysql:host=%s;dbname=%s;charset=utf8mb4', DB_HOST, DB_NAME);
            $option = array(
                PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                // 强制开启查询缓冲：避免「2014 Cannot execute queries while other
                // unbuffered queries are active」。该连接在多处被复用（单例），
                // 若不缓冲，前一条语句的结果集未取完就会阻塞后续查询。
                PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true,
            );

            $pdo = new PDO($dsn, DB_USER, DB_PASS, $option);
            // 部分环境在构造选项里设置不生效，再显式 setAttribute 兜底
            $pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
            return self::$pdo = $pdo;
        } catch (PDOException $e) {
            error_log('DB connection error: ' . $e->getMessage());
            exit('数据库连接失败，请联系管理员');
        }
    }
}