<?php
/**
 * 数据库适配层 —— SQLite 单文件后端（零配置、无需额外服务）
 *
 * 设计要点：
 * 1. 数据文件固定为 data/ny.db（SQLite），不需要用户配置任何连接信息。
 * 2. 若环境没有 pdo_sqlite 扩展，整个层自动降级为「不可用」，
 *    上层（Roster / 配置）会回退到 JSON 文件存储 —— 保证老环境不会挂。
 * 3. 所有建表/加列都是幂等的（IF NOT EXISTS / 探测列后 ALTER），可重复执行。
 * 4. 首次启用时自动把已有的 data/roster.json、data/config.json 迁移进来，
 *    老数据不丢（迁移只发生在目标表为空时）。
 *
 * 表结构：
 *   ny_settings       (k TEXT PK, v TEXT)              全局配置（键 'config' 存整份配置 JSON）
 *   ny_roster         (sid TEXT PK, name, cls, grp, login)
 *   ny_project_config (project_id TEXT PK, config_json TEXT)  每份试卷独立配置（满分/合格率/免考，试卷间隔离）
 */
declare(strict_types=1);

class Db
{
    private static ?PDO $pdo = null;
    private static string $err = '';
    private static bool $initTried = false;

    public static function prefix(): string
    {
        return 'ny_';
    }

    /** 数据文件路径 */
    public static function dbFile(): string
    {
        return NY_DATA . '/ny.db';
    }

    /** 是否具备启用条件（有 pdo_sqlite 扩展） */
    public static function isConfigured(): bool
    {
        return extension_loaded('pdo_sqlite');
    }

    /** 是否已真正连上 */
    public static function isConnected(): bool
    {
        return self::pdo() !== null;
    }

    public static function driver(): string
    {
        return self::pdo() !== null ? 'sqlite' : '';
    }

    public static function lastError(): string
    {
        return self::$err;
    }

    /** 建立/复用连接；失败返回 null 而不抛异常（上层要能优雅降级） */
    public static function connect(array $p = []): PDO
    {
        if (self::$pdo instanceof PDO) {
            return self::$pdo;
        }
        if (!self::isConfigured()) {
            self::$err = 'PHP 未启用 pdo_sqlite 扩展，已回退到文件存储';
            throw new RuntimeException(self::$err);
        }
        $file = self::dbFile();
        $dir  = dirname($file);
        if (!is_dir($dir)) {
            @mkdir($dir, 0777, true);
        }
        try {
            $pdo = new PDO('sqlite:' . $file, null, null, [
                PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
                PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                PDO::ATTR_EMULATE_PREPARES   => false,
            ]);
            // WAL + 合理超时，避免多人同时刷新时 "database is locked"
            $pdo->exec('PRAGMA journal_mode=WAL');
            $pdo->exec('PRAGMA synchronous=NORMAL');
            $pdo->exec('PRAGMA busy_timeout=5000');
            $pdo->exec('PRAGMA foreign_keys=ON');
            self::$pdo = $pdo;
            self::$err = '';
            self::migrate();
            return $pdo;
        } catch (Throwable $e) {
            self::$pdo = null;
            self::$err = $e->getMessage();
            throw new RuntimeException('SQLite 连接失败：' . $e->getMessage());
        }
    }

    /** 获取连接（不可用返回 null） */
    public static function pdo(): ?PDO
    {
        if (self::$pdo instanceof PDO) {
            return self::$pdo;
        }
        if (self::$initTried) {
            return null; // 已经试过且失败，不再反复重试（每次请求最多试一次）
        }
        self::$initTried = true;
        try {
            return self::connect();
        } catch (Throwable $e) {
            return null;
        }
    }

    /** 建表 + 索引（幂等，可重复调用） */
    public static function migrate(): int
    {
        $pdo = self::$pdo;
        if (!$pdo) {
            return 0;
        }
        $p = self::prefix();
        $pdo->exec("CREATE TABLE IF NOT EXISTS {$p}settings (
            k TEXT PRIMARY KEY,
            v TEXT NOT NULL DEFAULT '',
            updated_at INTEGER NOT NULL DEFAULT 0
        )");
        $pdo->exec("CREATE TABLE IF NOT EXISTS {$p}roster (
            sid   TEXT PRIMARY KEY,
            name  TEXT NOT NULL DEFAULT '',
            cls   TEXT NOT NULL DEFAULT '',
            grp   TEXT NOT NULL DEFAULT '',
            login TEXT NOT NULL DEFAULT '',
            sort  INTEGER NOT NULL DEFAULT 0,
            updated_at INTEGER NOT NULL DEFAULT 0
        )");
        $pdo->exec("CREATE TABLE IF NOT EXISTS {$p}project_config (
            project_id  TEXT PRIMARY KEY,
            config_json TEXT NOT NULL DEFAULT '{}',
            updated_at  INTEGER NOT NULL DEFAULT 0
        )");
        $pdo->exec("CREATE INDEX IF NOT EXISTS idx_{$p}roster_cls ON {$p}roster(cls)");
        self::ensureRosterLogin();
        return 3;
    }

    /** 旧库缺少 login 列时补上（幂等） */
    public static function ensureRosterLogin(): void
    {
        $pdo = self::$pdo;
        if (!$pdo) {
            return;
        }
        $p = self::prefix();
        try {
            $cols = $pdo->query("PRAGMA table_info({$p}roster)")->fetchAll(PDO::FETCH_ASSOC);
            $has = false;
            foreach ($cols as $c) {
                if (($c['name'] ?? '') === 'login') {
                    $has = true;
                    break;
                }
            }
            if (!$has) {
                $pdo->exec("ALTER TABLE {$p}roster ADD COLUMN login TEXT NOT NULL DEFAULT ''");
            }
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
        }
    }

    // ---------------- 设置 ----------------


    /**
     * SQLite 用 ON CONFLICT 做 upsert（其它方言见历史版本）
     *
     * 返回是否真的写成功：以前这里 void + 内部吞异常，导致"配置没落盘但上层以为成功"
     * （典型后果：登录成功→下一请求仍报"未配置账号"→反复跳登录页的死循环）。
     * 因此改为回读校验后返回 bool，并把失败原因放进 self::lastError()。
     */
    public static function settingsSet(string $k, string $v): bool
    {
        $pdo = self::pdo();
        if (!$pdo) {
            return false;
        }
        try {
            $p = self::prefix();
            $st = $pdo->prepare(
                "INSERT INTO {$p}settings (k, v, updated_at) VALUES (?, ?, ?)
                 ON CONFLICT(k) DO UPDATE SET v=excluded.v, updated_at=excluded.updated_at"
            );
            $st->execute([$k, $v, time()]);
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return false;
        }
        // 回读校验：磁盘满 / 目录不可写 / 只读挂载时 execute 可能不报错但实际未落盘
        try {
            $p  = self::prefix();
            $st = $pdo->prepare("SELECT v FROM {$p}settings WHERE k = ?");
            $st->execute([$k]);
            $got = $st->fetchColumn();
            if ($got === false || (string)$got !== $v) {
                self::$err = '写入后回读不一致（可能磁盘已满或数据库只读）';
                return false;
            }
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return false;
        }
        return true;
    }

    public static function settingsDelete(string $k): void
    {
        $pdo = self::pdo();
        if (!$pdo) {
            return;
        }
        try {
            $p  = self::prefix();
            $st = $pdo->prepare("DELETE FROM {$p}settings WHERE k = ?");
            $st->execute([$k]);
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
        }
    }

    public static function settingsGet(string $k, string $def = ''): string
    {
        $pdo = self::pdo();
        if (!$pdo) {
            return $def;
        }
        try {
            $p = self::prefix();
            $st = $pdo->prepare("SELECT v FROM {$p}settings WHERE k = ?");
            $st->execute([$k]);
            $v = $st->fetchColumn();
            return $v === false ? $def : (string)$v;
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return $def;
        }
    }

    // ---------------- 名单 ----------------

    public static function rosterAll(): array
    {
        $pdo = self::pdo();
        if (!$pdo) {
            return [];
        }
        try {
            $p = self::prefix();
            $st = $pdo->query("SELECT sid, name, cls, grp, login FROM {$p}roster ORDER BY sort ASC, sid ASC");
            $out = [];
            foreach ($st->fetchAll(PDO::FETCH_ASSOC) as $r) {
                $out[] = [
                    'sid'   => (string)($r['sid'] ?? ''),
                    'name'  => (string)($r['name'] ?? ''),
                    'cls'   => (string)($r['cls'] ?? ''),
                    'grp'   => (string)($r['grp'] ?? ''),
                    'login' => (string)($r['login'] ?? ''),
                ];
            }
            return $out;
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return [];
        }
    }

    /**
     * 全量替换名单（roster_save 语义）
     * @return bool 成功 true；DB 不可用或事务失败 false（失败原因见 lastError）
     */
    public static function rosterReplace(array $students): bool
    {
        $pdo = self::pdo();
        if (!$pdo) {
            self::$err = '数据库未连接';
            return false;
        }
        try {
            $p = self::prefix();
            $pdo->beginTransaction();
            $pdo->exec("DELETE FROM {$p}roster");
            $st = $pdo->prepare(
                "INSERT INTO {$p}roster (sid, name, cls, grp, login, sort, updated_at)
                 VALUES (?, ?, ?, ?, ?, ?, ?)"
            );
            $i = 0;
            foreach ($students as $s) {
                if (!is_array($s)) {
                    continue;
                }
                $st->execute([
                    (string)($s['sid'] ?? ''),
                    (string)($s['name'] ?? ''),
                    (string)($s['cls'] ?? ''),
                    (string)($s['grp'] ?? ''),
                    (string)($s['login'] ?? ''),
                    $i++,
                    time(),
                ]);
            }
            $pdo->commit();
            return true;
        } catch (Throwable $e) {
            if ($pdo->inTransaction()) {
                $pdo->rollBack();
            }
            self::$err = $e->getMessage();
            return false;
        }
    }

    public static function rosterCount(): int
    {
        $pdo = self::pdo();
        if (!$pdo) {
            return 0;
        }
        try {
            $p = self::prefix();
            return (int)$pdo->query("SELECT COUNT(*) FROM {$p}roster")->fetchColumn();
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return 0;
        }
    }

    // ---------------- 每卷独立配置（满分 / 合格率 / 免考名单） ----------------


    /** @return array 单卷配置（缺省返回空结构） */
    public static function projectConfigGet(string $projectId): array
    {
        $def = ['full_score' => null, 'pass_rate' => null, 'exempt' => []];
        if ($projectId === '') {
            return $def;
        }
        $pdo = self::pdo();
        if (!$pdo) {
            return $def;
        }
        try {
            $p = self::prefix();
            $st = $pdo->prepare("SELECT config_json FROM {$p}project_config WHERE project_id = ?");
            $st->execute([$projectId]);
            $v = $st->fetchColumn();
            if ($v === false) {
                return $def;
            }
            $j = json_decode((string)$v, true);
            return is_array($j) ? array_merge($def, $j) : $def;
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
            return $def;
        }
    }

    /** 写入单卷配置（整份覆盖；null 表示"用全局默认"） */
    public static function projectConfigSet(string $projectId, array $cfg): void
    {
        if ($projectId === '') {
            return;
        }
        $pdo = self::pdo();
        if (!$pdo) {
            return;
        }
        try {
            $p = self::prefix();
            $st = $pdo->prepare(
                "INSERT INTO {$p}project_config (project_id, config_json, updated_at) VALUES (?, ?, ?)
                 ON CONFLICT(project_id) DO UPDATE SET config_json=excluded.config_json, updated_at=excluded.updated_at"
            );
            $st->execute([$projectId, json_encode($cfg, JSON_UNESCAPED_UNICODE), time()]);
        } catch (Throwable $e) {
            self::$err = $e->getMessage();
        }
    }

}