<?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);

function qdb_column_exists(PDO $pdo, string $table, string $column): bool {
    $stmt = $pdo->query('PRAGMA table_info(' . $table . ')');
    foreach ($stmt->fetchAll(PDO::FETCH_ASSOC) as $col) {
        if (($col['name'] ?? '') === $column) {
            return true;
        }
    }
    return false;
}

/**
 * Apply incremental schema fixes. Returns true if the temp DB was modified.
 */
function qdb_apply_migrations(PDO $pdo, string $schemaSql): bool {
    $changed = false;

    if (!qdb_column_exists($pdo, 'questionnaire', 'categoryKey')) {
        $pdo->exec("ALTER TABLE questionnaire ADD COLUMN categoryKey TEXT NOT NULL DEFAULT ''");
        $changed = true;
    }

    $currentVersion = (int)$pdo->query('PRAGMA user_version')->fetchColumn();
    if ($currentVersion < QDB_VERSION) {
        $pdo->exec('PRAGMA foreign_keys = OFF;');
        $pdo->exec($schemaSql);
        if (!qdb_column_exists($pdo, 'questionnaire', 'categoryKey')) {
            $pdo->exec("ALTER TABLE questionnaire ADD COLUMN categoryKey TEXT NOT NULL DEFAULT ''");
        }
        $pdo->exec('PRAGMA user_version = ' . QDB_VERSION . ';');
        $pdo->exec('PRAGMA foreign_keys = ON;');
        $changed = true;
    }

    return $changed;
}

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

/**
 * 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;");

    $schemaChanged = qdb_apply_migrations($pdo, $sql);

    // Read-only opens discard the temp file; persist one-off migrations to the master DB.
    if ($schemaChanged && !$writable) {
        $migrateLock = qdb_acquire_lock();
        try {
            qdb_save($tmpDb, $migrateLock);
        } catch (Throwable $e) {
            @unlink($tmpDb);
            flock($migrateLock, LOCK_UN);
            fclose($migrateLock);
            throw $e;
        }
        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);
    }
}