<?php
/**
 * PDO 数据库连接类（单例模式）
 * 用法：$pdo = DB::getInstance()->getPdo();
 */
class DB
{
    private static $instance = null;
    private $pdo;

    private function __construct()
    {
        $cfg = require __DIR__ . '/../../config/database.php';
        $dsn = sprintf(
            'mysql:host=%s;port=%d;dbname=%s;charset=%s',
            $cfg['host'],
            $cfg['port'],
            $cfg['dbname'],
            $cfg['charset']
        );
        $this->pdo = new PDO($dsn, $cfg['username'], $cfg['password'], [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES   => false,
        ]);
    }

    public static function getInstance()
    {
        if (self::$instance === null) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    public function getPdo()
    {
        return $this->pdo;
    }

    // 禁止克隆
    private function __clone() {}
}