<?php
/**
 * 数据库连接层（统一 PDO）
 *
 * 支持 PostgreSQL / MariaDB(MySQL) / SQLite(主要用于本地无 DB 时的降级与测试)。
 * 连接参数存于 data/db.json；通过 Db::instance() 取单例连接。
 * 未配置数据库时返回 null，上层回退到文件存储（config.json / roster.json）。
 */
declare(strict_types=1);

class Db
{
    /** @var PDO|null */
    private static $pdo = null;
    private static string $driver = '';
    private static bool $tried = false;
    private static bool $failed = false;
    private static string $lastError = '';

    /** 数据库连接参数文件 */
    public static function dbFile(): string
    {
        return NY_DATA . '/db.json';
    }

    /** 是否已配置数据库（db.json 存在且有 driver/host 等） */
    public static function isConfigured(): bool
    {
        $d = self::params();
        return !empty($d['driver']);
    }

    /** 读取连接参数 */
    public static function params(): array
    {
        $d = ny_read_json(self::dbFile(), null);
        if (!is_array($d)) {
            return [];
        }
        return $d;
    }

    /** 写入连接参数 */
    public static function saveParams(array $p): bool
    {
        return ny_write_json(self::dbFile(), $p);
    }

    /** 当前驱动名（用于 SQL 方言）：mysql | pgsql | sqlite | '' */
    public static function driver(): string
    {
        self::check();
        return self::$driver;
    }

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

    /** 上一次连接失败的原因（连接正常时为空） */
    public static function lastError(): string
    {
        self::check();
        return self::$lastError;
    }

    /**
     * 获取 PDO 单例；未配置或连不上返回 null。
     */
    public static function pdo(): ?PDO
    {
        self::check();
        return self::$pdo;
    }

    private static function check(): void
    {
        if (self::$tried) {
            return;
        }
        self::$tried = true;
        $p = self::params();
        $driver = strtolower((string)($p['driver'] ?? ''));
        if ($driver === '') {
            return;
        }
        self::$driver = $driver;
        try {
            self::$pdo = self::connect($p);
        } catch (Throwable $e) {
            self::$failed = true;
            self::$pdo = null;
            self::$lastError = $e->getMessage();
        }
    }

    /** 根据参数建 PDO 连接 */
    public static function connect(array $p): PDO
    {
        $driver = strtolower((string)($p['driver'] ?? ''));
        $host = (string)($p['host'] ?? '127.0.0.1');
        $port = (int)($p['port'] ?? 0);
        $db   = (string)($p['dbname'] ?? ($p['database'] ?? ''));
        $user = (string)($p['user'] ?? ($p['username'] ?? ''));
        $pass = (string)($p['password'] ?? '');

        $options = [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES   => false,
        ];

        if ($driver === 'sqlite') {
            $dsn = 'sqlite:' . ($p['path'] ?? ($db ?: (NY_DATA . '/app.sqlite')));
        } elseif ($driver === 'pgsql') {
            $dsn = 'pgsql:host=' . $host;
            if ($port > 0) {
                $dsn .= ';port=' . $port;
            }
            $dsn .= ';dbname=' . $db;
            $dsn .= ';user=' . $user;
            $dsn .= ';password=' . $pass;
        } else { // mysql / mariadb
            $dsn = 'mysql:host=' . $host;
            if ($port > 0) {
                $dsn .= ';port=' . $port;
            }
            $dsn .= ';dbname=' . $db . ';charset=utf8mb4';
            $options[PDO::ATTR_PERSISTENT] = false;
        }

        $pdo = new PDO($dsn, $user, $pass, $options);
        if ($driver === 'mysql') {
            $pdo->exec("SET NAMES utf8mb4");
        }
        return $pdo;
    }

    /** 表名前缀 */
    public static function prefix(): string
    {
        return 'ny_';
    }

    /**
     * 建表（幂等）。返回已执行语句数量。
     * 用通用 SQL，三方言均可执行（表名/列名小写、规范命名）。
     */
    public static function migrate(): int
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            throw new RuntimeException('数据库未连接，无法初始化表结构');
        }
        $driver = self::$driver;
        $n = 0;

        // settings(key,value) —— 系统设置键值表
        if ($driver === 'sqlite') {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_settings (' .
                'k VARCHAR(128) PRIMARY KEY, ' .
                'v TEXT)';
        } elseif ($driver === 'pgsql') {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_settings (' .
                'k VARCHAR(128) PRIMARY KEY, ' .
                'v TEXT)';
        } else {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_settings (' .
                '`k` VARCHAR(128) NOT NULL PRIMARY KEY, ' .
                '`v` TEXT) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4';
        }
        $pdo->exec($sql); $n++;

        // roster —— 名单表（学号/姓名/班级/组别/登陆账号）
        if ($driver === 'sqlite') {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_roster (' .
                'id INTEGER PRIMARY KEY AUTOINCREMENT, ' .
                'sid VARCHAR(64), name VARCHAR(128), cls VARCHAR(64), grp VARCHAR(32), login VARCHAR(64))';
        } elseif ($driver === 'pgsql') {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_roster (' .
                'id SERIAL PRIMARY KEY, ' .
                'sid VARCHAR(64), name VARCHAR(128), cls VARCHAR(64), grp VARCHAR(32), login VARCHAR(64))';
        } else {
            $sql = 'CREATE TABLE IF NOT EXISTS ny_roster (' .
                'id INT AUTO_INCREMENT PRIMARY KEY, ' .
                'sid VARCHAR(64), name VARCHAR(128), cls VARCHAR(64), grp VARCHAR(32), login VARCHAR(64)) ' .
                'ENGINE=InnoDB DEFAULT CHARSET=utf8mb4';
        }
        $pdo->exec($sql); $n++;

        // 旧版本升级：补 login 列
        self::ensureRosterLogin();

        return $n;
    }

    /** 旧表升级：ny_roster 缺 login 列时自动补（三方言兼容） */
    public static function ensureRosterLogin(): void
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return;
        }
        $has = false;
        if (self::$driver === 'sqlite') {
            foreach ($pdo->query('PRAGMA table_info(ny_roster)')->fetchAll() as $c) {
                if (strtolower((string)$c['name']) === 'login') {
                    $has = true;
                    break;
                }
            }
        } elseif (self::$driver === 'pgsql') {
            $st = $pdo->prepare("SELECT COUNT(*) FROM information_schema.columns " .
                "WHERE table_name = 'ny_roster' AND column_name = 'login'");
            $st->execute();
            $has = (int)$st->fetchColumn() > 0;
        } else {
            $has = $pdo->query("SHOW COLUMNS FROM ny_roster LIKE 'login'")->fetch() !== false;
        }
        if (!$has) {
            $pdo->exec('ALTER TABLE ny_roster ADD COLUMN login VARCHAR(64)');
        }
    }

    /**
     * 把所有 settings 读成数组
     */
    public static function settingsAll(): array
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return [];
        }
        $out = [];
        $stmt = $pdo->query('SELECT k, v FROM ny_settings');
        foreach ($stmt->fetchAll() as $row) {
            $out[$row['k']] = $row['v'];
        }
        return $out;
    }

    public static function settingsSet(string $k, string $v): void
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return;
        }
        $drv = self::$driver;
        if ($drv === 'pgsql') {
            $sql = 'INSERT INTO ny_settings(k, v) VALUES(?, ?) ' .
                   'ON CONFLICT (k) DO UPDATE SET v = EXCLUDED.v';
        } elseif ($drv === 'sqlite') {
            $sql = 'INSERT OR REPLACE INTO ny_settings(k, v) VALUES(?, ?)';
        } else {
            $sql = 'INSERT INTO ny_settings(k, v) VALUES(?, ?) ' .
                   'ON DUPLICATE KEY UPDATE v = VALUES(v)';
        }
        $pdo->prepare($sql)->execute([$k, $v]);
    }

    /** 名单：全量读 */
    public static function rosterAll(): array
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return [];
        }
        self::ensureRosterLogin();
        $stmt = $pdo->query('SELECT sid, name, cls, grp, login FROM ny_roster ORDER BY id');
        $rows = [];
        foreach ($stmt->fetchAll() as $r) {
            $rows[] = [
                'sid'   => (string)$r['sid'],
                'name'  => (string)$r['name'],
                'cls'   => (string)$r['cls'],
                'grp'   => (string)$r['grp'],
                'login' => (string)($r['login'] ?? ''),
            ];
        }
        return $rows;
    }

    /** 名单：清空后全量写 */
    public static function rosterReplace(array $students): void
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return;
        }
        self::ensureRosterLogin();
        $pdo->beginTransaction();
        try {
            $pdo->exec('DELETE FROM ny_roster');
            $st = $pdo->prepare('INSERT INTO ny_roster(sid, name, cls, grp, login) VALUES(?, ?, ?, ?, ?)');
            foreach ($students as $s) {
                $st->execute([
                    (string)($s['sid'] ?? ''),
                    (string)($s['name'] ?? ''),
                    (string)($s['cls'] ?? ''),
                    (string)($s['grp'] ?? ''),
                    (string)($s['login'] ?? ''),
                ]);
            }
            $pdo->commit();
        } catch (Throwable $e) {
            $pdo->rollBack();
            throw $e;
        }
    }

    /** 名单：行数 */
    public static function rosterCount(): int
    {
        $pdo = self::pdo();
        if ($pdo === null) {
            return 0;
        }
        return (int)$pdo->query('SELECT COUNT(*) FROM ny_roster')->fetchColumn();
    }
}