fetchNavs function

Future<String> fetchNavs(String url)

Method to fetch NAV data from the URL Given a URL, this function fetches the data from the given URL. It resolves with the fetched data if there is no error. Otherwise, it rejects with an error message. @param {String} url - URL to fetch data from @returns {Future<String>}

The NAV data is updated every business day at 11:00 PM IST.

Implementation

Future<String> fetchNavs(String url) async {
  final cacheDir = await getTemporaryDirectory();
  final cacheFile = File('${cacheDir.path}/nav_data.txt');
  final cacheExpiryFile = File('${cacheDir.path}/nav_data_expiry.txt');

  // Check if cache exists and is not expired
  if (await cacheFile.exists() && await cacheExpiryFile.exists()) {
    final expiryDateStr = await cacheExpiryFile.readAsString();
    final expiryDate = DateTime.parse(expiryDateStr);
    final indianTime =
        DateTime.now().toUtc().add(Duration(hours: 5, minutes: 30));
    // if the time is before 11:00 PM IST and the cache is not expired
    if (indianTime.isBefore(expiryDate) && indianTime.hour < 23) {
      // Load from cache
      return await cacheFile.readAsString();
    } else {
      logger.i('Cache expired or invalid time, fetching from URL');
    }
  } else {
    logger.e('Cache files do not exist, fetching from URL');
  }

  final response = await http.get(Uri.parse(url));
  if (response.statusCode == 200) {
    // load the data from URL.
    final result = response.body;

    if (isError(result)) {
      throw "Error in fetching NAVs."; // Check for errors
    } else {
      // Save data to cache
      await cacheFile.writeAsString(result);
      // Set cache expiry to 11:00 PM IST
      final now = DateTime.now().toUtc().add(Duration(hours: 5, minutes: 30));
      final expiryDate = DateTime(now.year, now.month, now.day, 23, 0, 0);
      await cacheExpiryFile.writeAsString(expiryDate.toIso8601String());
      return result; // Resolve the fetched text
    }
  } else {
    throw "Error fetching data."; // Reject in case of an error
  }
}