<?php
declare(strict_types=1);

final class BackendRuntimeConfig
{
    public static function sync(Settings $settings, string $backendScript, string $statePath = Settings::CONFIG_DIR . '/backend-state.json', string $errorLog = ''): void
    {
        $desired = $settings->backendMode();
        $current = self::currentBackend($statePath);
        if ($current === $desired) {
            return;
        }

        if (!is_file($backendScript) || !is_executable($backendScript)) {
            self::log($errorLog, 'Backend script not executable: ' . $backendScript);
            return;
        }

        $process = proc_open([$backendScript, $desired], [['pipe', 'r'], ['pipe', 'w'], ['pipe', 'w']], $pipes);
        if (!is_resource($process)) {
            self::log($errorLog, 'Could not start backend script.');
            return;
        }
        fclose($pipes[0]);
        stream_get_contents($pipes[1]);
        $stderr = stream_get_contents($pipes[2]);
        fclose($pipes[1]);
        fclose($pipes[2]);
        $code = proc_close($process);
        if ($code !== 0) {
            self::log($errorLog, 'Backend script failed with code ' . $code . ': ' . trim($stderr));
        }
    }

    private static function currentBackend(string $statePath): string
    {
        if (!is_file($statePath)) {
            return '';
        }
        $data = json_decode((string)file_get_contents($statePath), true);
        return is_array($data) ? (string)($data['active_backend'] ?? '') : '';
    }

    private static function log(string $errorLog, string $message): void
    {
        if ($errorLog === '') {
            return;
        }
        @error_log('[' . date('c') . '] BACKEND_SYNC ' . $message . "\n", 3, $errorLog);
    }
}