meincantor-app/lib/cache_manager.dart

import 'dart:convert';

import 'package:flutter_cache_manager/flutter_cache_manager.dart';
import 'package:shared_preferences/shared_preferences.dart';

Future<String> getCachedTimetable(String ext, String? presetClassNum) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  String classNum;
  if (presetClassNum != null) {
    classNum = presetClassNum.replaceAll("/", "_");
  } else if (prefs.getString('class_num') != null) {
    classNum = prefs.getString('class_num')!.replaceAll("/", "_");
  } else {
    classNum = '05_1';
  }
  var apiKey = prefs.getString('api_key');
  var headers = {"x-api-key": "$apiKey"};
  var file = await DefaultCacheManager().getSingleFile(
      "https://mein.cantorgymnasium.de/api/timetable/$ext/$classNum",
      headers: headers);
  return (utf8.decode(await file.readAsBytes()));
}