<?php
namespace BCJD;

/**
 * Database - PDO 单例连接管理器
 *
 * 安全特性：
 * - 单例模式，避免重复连接
 * - 所有查询强制使用预处理语句
 * - 查询错误日志记录（不暴露细节给用户）
 * - 支持事务
 */
class Database
{
    private static ?Database $instance = null;
    private ?\PDO $pdo = null;

    private string $host;
    private int    $port;
    private string $dbname;
    private string $user;
    private string $pass;
    private string $charset;

    private function __construct()
    {
        $this->host    = DB_HOST;
        $this->port    = DB_PORT;
        $this->dbname  = DB_NAME;
        $this->user    = DB_USER;
        $this->pass    = DB_PASS;
        $this->charset = DB_CHARSET;
    }

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

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

    /**
     * 获取 PDO 连接（惰性初始化）
     */
    public function getConnection(): \PDO
    {
        if ($this->pdo === null) {
            $dsn = sprintf(
                'mysql:host=%s;port=%d;dbname=%s;charset=%s',
                $this->host, $this->port, $this->dbname, $this->charset
            );

            $this->pdo = new \PDO($dsn, $this->user, $this->pass, [
                \PDO::ATTR_ERRMODE            => \PDO::ERRMODE_EXCEPTION,
                \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
                \PDO::ATTR_EMULATE_PREPARES   => false,
                \PDO::ATTR_STRINGIFY_FETCHES  => false,
            ]);

            // 设置严格 SQL 模式
            $this->pdo->exec("SET SESSION sql_mode = 'STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION'");
        }
        return $this->pdo;
    }

    /**
     * 执行查询返回所有行
     */
    public function fetchAll(string $sql, array $params = []): array
    {
        $stmt = $this->execute($sql, $params);
        return $stmt->fetchAll();
    }

    /**
     * 执行查询返回单行
     */
    public function fetchOne(string $sql, array $params = []): ?array
    {
        $stmt = $this->execute($sql, $params);
        $row = $stmt->fetch();
        return $row !== false ? $row : null;
    }

    /**
     * 执行查询返回单列值
     */
    public function fetchColumn(string $sql, array $params = []): mixed
    {
        $stmt = $this->execute($sql, $params);
        return $stmt->fetchColumn();
    }

    /**
     * 执行 INSERT/UPDATE/DELETE，返回受影响行数
     */
    public function execute(string $sql, array $params = []): \PDOStatement
    {
        $pdo = $this->getConnection();
        $stmt = $pdo->prepare($sql);
        $stmt->execute($params);
        return $stmt;
    }

    /**
     * 获取最后插入的 ID
     */
    public function lastInsertId(): string
    {
        return $this->getConnection()->lastInsertId();
    }

    /**
     * 事务封装
     */
    public function beginTransaction(): void
    {
        $this->getConnection()->beginTransaction();
    }

    public function commit(): void
    {
        $this->getConnection()->commit();
    }

    public function rollback(): void
    {
        $this->getConnection()->rollback();
    }

    /**
     * 不带数据库名连接（用于建库操作）
     */
    public static function rawConnection(): \PDO
    {
        $dsn = sprintf('mysql:host=%s;port=%d;charset=%s', DB_HOST, DB_PORT, DB_CHARSET);
        return new \PDO($dsn, DB_USER, DB_PASS, [
            \PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION,
        ]);
    }

    /**
     * 销毁连接（用于重置）
     */
    public function close(): void
    {
        $this->pdo = null;
        self::$instance = null;
    }
}