simple remote config loader with persistent (default config if loads via network fails). Reference : https://www.donnywals.com/building-a-simple-remote-configuration-for-your-apps/

simple_remote_config.swift

class LocalConfigLoader: LocalConfigLoading {
  private var cachedConfigUrl: URL? {
    guard let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else {
      return nil
    }

    return documentsUrl.appendingPathComponent("config.json")
  }

  private var cachedConfig: AppConfig? {
    let jsonDecoder = JSONDecoder()

    guard let configUrl = cachedConfigUrl,
          let data = try? Data(contentsOf: configUrl),
          let config = try? jsonDecoder.decode(AppConfig.self, from: data) else {
      return nil
    }

    return config
  }

  private var defaultConfig: AppConfig {
    let jsonDecoder = JSONDecoder()

    guard let url = Bundle.main.url(forResource: "config", withExtension: "json"),
          let data = try? Data(contentsOf: url),
          let config = try? jsonDecoder.decode(AppConfig.self, from: data) else {
      fatalError("Bundle must include default config. Check and correct this mistake.")
    }

    return config
  }

  func fetch() -> AppConfig {
    if let cachedConfig = self.cachedConfig {
      return cachedConfig
    } else {
      let config = self.defaultConfig
      persist(config)
      return config
    }
  }

  func persist(_ config: AppConfig) {
    guard let configUrl = cachedConfigUrl else {
      // should never happen, you might want to handle this
      return
    }

    do {
      let encoder = JSONEncoder()
      let data = try encoder.encode(config)
      try data.write(to: configUrl)
    } catch {
      // you could forward this error somewhere
      print(error)
    }
  }
}