<?php

declare(strict_types=1);

const DASHBOARD_BVG_STOP = '900086103';

function dashboard_fetch_departures(): array
{
    $directory = __DIR__ . '/../cache';
    if (!is_dir($directory) && !@mkdir($directory, 0775, true) && !is_dir($directory)) {
        throw new RuntimeException('BVG-Cache nicht beschreibbar.');
    }
    $file = fopen($directory . '/bvg-' . DASHBOARD_BVG_STOP . '.json', 'c+');
    if (!$file) {
        throw new RuntimeException('BVG-Cache nicht verfügbar.');
    }
    try {
        // Gemeinsamer Cache: alle 12 Sekunden und zusätzlich zum Minutenwechsel.
        if (!flock($file, LOCK_EX)) {
            throw new RuntimeException('BVG-Cache konnte nicht gesperrt werden.');
        }
        $cache = json_decode(stream_get_contents($file), true) ?: [];
        if (microtime(true) >= ($cache['retryAt'] ?? 0)) {
            try {
                $data = dashboard_http_json('https://v6.bvg.transport.rest/stops/' . DASHBOARD_BVG_STOP . '/departures?'
                    . 'duration=120&results=30&bus=true&suburban=false&subway=false&tram=false'
                    . '&ferry=false&express=false&regional=false&remarks=false&language=de&pretty=false');
                if (!isset($data['departures']) || !is_array($data['departures'])) {
                    throw new RuntimeException('Unerwartete BVG-Antwort.');
                }
                $now = microtime(true);
                $cache = ['departures' => array_values(array_filter($data['departures'], static fn(array $d): bool =>
                    ($d['line']['product'] ?? '') === 'bus'
                    && in_array($d['stop']['id'] ?? '', [DASHBOARD_BVG_STOP, '900000' . substr(DASHBOARD_BVG_STOP, 3)], true))),
                    'updatedAt' => (int) round($now * 1000), 'retryAt' => min($now + 12, (floor($now / 60) + 1) * 60),
                    'unavailable' => false];
            } catch (Throwable $error) {
                // Letzte Antwort behalten; auch bei 429/503 nicht sofort erneut anfragen.
                error_log('Dashboard BVG: ' . $error->getMessage());
                $cache['unavailable'] = true;
                $cache['retryAt'] = microtime(true) + 30;
            }
            rewind($file);
            $json = json_encode($cache, JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR);
            if (!ftruncate($file, 0) || fwrite($file, $json) !== strlen($json) || !fflush($file)) {
                throw new RuntimeException('BVG-Cache konnte nicht gespeichert werden.');
            }
        }
        return $cache + ['departures' => [], 'updatedAt' => 0];
    } finally {
        fclose($file);
    }
}