currency_converter.rb

class Helper::CurrencyConverter

  CACHE_EXPIRY = 1.minute

  def initialize(base_currency, target_currency, api_client = OpenExchangeRates::Rates.new)
    @base_currency   = base_currency
    @target_currency = target_currency
    @api_client = api_client
  end


  # Converts the specified amount from the base currency to the target currency.
  # Returns the converted amount rounded to 2 decimal places.
  def convert(amount)
    rate = get_rate
    (amount * rate).round(2) if rate
  end

  private

  # Retrieves the exchange rate for the specified target currency.
  # Caches the result for CACHE_EXPIRY duration.
  # If an error occurs, logs the error and notifies via Slack.
  def get_rate
    Rails.cache.fetch(rate_cache_key(@target_currency), expires_in: CACHE_EXPIRY) do
      Rails.logger.info("Fetching exchange rate for #{@base_currency} to #{@target_currency}")
      begin
        @api_client.exchange_rate(from: @base_currency, to: @target_currency)
      rescue StandardError => e
        Rails.logger.error("Could not retrieve currency conversion data from Open Exchange Rates API: #{e}")
        notify_error(e)
        nil
      end
    end
  end

  # Generates a cache key for the exchange rate between the base currency and the target currency.
  def rate_cache_key
    "rate_#{@base_currency}_#{@target_currency}"
  end

  # Notifies the Slack channel about the currency conversion error.
  def notify_error(error)
    Notification::Slack.new.send_conversion_errors(error)
  end
end