04102020-iOS-SimpleMath-solution.swift

#warning("Documentation needs work.")
#warning("Who is calling `storedData`? Why is it private?")
/// What data?
/// - The cache, if available.
/// - If the cache is not available, try from UserDefaults
/// - If UserDefaults doesn't have any data, then return `defaultStoreData`
///
/// - Returns: a Store Data object?
private var storedData: StoredData {

  // Do we have a cache?
  guard let cache = storedDataCache else {

    // We do not. Do we have the previous data in UserDefaults?
    guard let savedJSONData = UserDefaults.standard.value(forKey: key) as? Data else {
      // We don't have previous data.
      // Generate it.
      print("No data found for key \(key), generating default values")
      storedDataCache = defaultStoreData
      #warning("We should save this to UserDefaults.")
      return storedDataCache!
    }

    // We do have the previous data in UserDefaults.
    // Transform it into a JSON.
    var storedData = defaultStoreData
    do {
      storedData = try JSONDecoder().decode(StoredData.self, from: savedJSONData)
    } catch {
      print("error reading stored data \(error), generating default values")
    }

    storedDataCache = storedData
    return storedData
  }

  return cache
}