<?php
// /var/www/html/db_init.php
// Shared helpers for opening, creating, and saving the encrypted SQLite database.
require_once __DIR__ . '/common.php';

define('QDB_PATH', __DIR__ . '/uploads/questionnaire_database');
define('QDB_LOCK', __DIR__ . '/uploads/.qdb_lock');
define('QDB_SCHEMA', __DIR__ . '/schema.sql');
define('QDB_VERSION', 4);

/**
 * Decrypt the master DB file into a temp SQLite file, or create a fresh one
 * from schema.sql if no DB exists yet.
 *
 * Returns [PDO $pdo, string $tmpPath, resource|null $lockFp].
 * If $writable is true, an exclusive lock is held -- caller MUST call
 * qdb_save() or qdb_discard() afterwards.
 */
function qdb_open(bool $writable = false): array {
    $dbPath = QDB_PATH;

    if (!is_dir(dirname($dbPath))) {
        if (!mkdir(dirname($dbPath), 0755, true) && !is_dir(dirname($dbPath))) {
            throw new Exception("Could not create uploads directory");
        }
    }

    $lockFp = null;
    if ($writable) {
        $lockFp = fopen(QDB_LOCK, 'c');
        if ($lockFp === false) throw new Exception("Could not open lock file");
        if (!flock($lockFp, LOCK_EX)) {
            fclose($lockFp);
            throw new Exception("Could not acquire lock");
        }
    }

    $tmpDb = tempnam(sys_get_temp_dir(), 'qdb_');
    $masterKey = get_master_key_bytes();

    $sql = file_get_contents(QDB_SCHEMA);
    if ($sql === false) {
        if ($lockFp) { flock($lockFp, LOCK_UN); fclose($lockFp); }
        throw new Exception("Could not read schema.sql");
    }

    if (file_exists($dbPath) && is_file($dbPath)) {
        $storedEnc = @file_get_contents($dbPath);
        if ($storedEnc === false) {
            if ($lockFp) { flock($lockFp, LOCK_UN); fclose($lockFp); }
            throw new Exception("Could not read stored DB");
        }
        $decrypted = aes256_cbc_decrypt_bytes($storedEnc, $masterKey);
        if (file_put_contents($tmpDb, $decrypted) === false) {
            if ($lockFp) { flock($lockFp, LOCK_UN); fclose($lockFp); }
            throw new Exception("Could not write temp DB");
        }
    } else {
        $pdo = new PDO("sqlite:$tmpDb");
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $pdo->exec($sql);
        $pdo->exec("PRAGMA user_version = " . QDB_VERSION . ";");
        $pdo = null;
    }

    $pdo = new PDO("sqlite:$tmpDb");
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $pdo->exec("PRAGMA foreign_keys = ON;");

    // Schema upgrade: apply CREATE TABLE IF NOT EXISTS for any missing tables
    $currentVersion = (int)$pdo->query("PRAGMA user_version")->fetchColumn();
    if ($currentVersion < QDB_VERSION) {
        $pdo->exec("PRAGMA foreign_keys = OFF;");
        $pdo->exec($sql);
        require_once __DIR__ . '/lib/migrate_v4.php';
        if ($currentVersion < 4) {
            qdb_migrate_v4($pdo);
        }
        $pdo->exec("PRAGMA user_version = " . QDB_VERSION . ";");
        $pdo->exec("PRAGMA foreign_keys = ON;");

        // Persist upgrade even when opened read-only (otherwise migration is lost on discard)
        if (!$writable) {
            qdb_save($tmpDb, $lockFp);
            return qdb_open(false);
        }
    }

    return [$pdo, $tmpDb, $lockFp];
}

/**
 * Encrypt the temp DB and atomically write it back to the master path.
 * Releases the lock.
 */
function qdb_save(string $tmpDb, $lockFp): void {
    $masterKey = get_master_key_bytes();
    $plainDb = file_get_contents($tmpDb);
    if ($plainDb === false) throw new Exception("Could not read temp DB for save");
    $enc = aes256_cbc_encrypt_bytes($plainDb, $masterKey);

    $dbPath = QDB_PATH;
    $tmpEncrypted = tempnam(dirname($dbPath), 'enc_qdb_');
    if (file_put_contents($tmpEncrypted, $enc) === false) {
        throw new Exception("Could not write encrypted DB");
    }
    if (!@rename($tmpEncrypted, $dbPath)) {
        if (!@copy($tmpEncrypted, $dbPath) || !@unlink($tmpEncrypted)) {
            throw new Exception("Could not save encrypted DB (rename/copy failed)");
        }
    }
    @chmod($dbPath, 0644);
    @unlink($tmpDb);

    if ($lockFp) {
        flock($lockFp, LOCK_UN);
        fclose($lockFp);
    }
}

/**
 * Discard changes -- clean up temp file and release lock without saving.
 */
function qdb_discard(string $tmpDb, $lockFp): void {
    @unlink($tmpDb);
    if ($lockFp) {
        @flock($lockFp, LOCK_UN);
        @fclose($lockFp);
    }
}