# File app/services/service/exchange_rates_provider.rb, line 12
def exchange_rates
  Rails.cache.fetch(cache_key) do
    rates = request_exchange_rates
    rates.presence || backup_file
  end
end

# File app/services/service/exchange_rates_provider.rb, line 4
def update_rates
  rates = request_exchange_rates
  if rates.present?
    Rails.cache.write(cache_key, rates)
    File.write(file_path, rates.to_json)
  end
end