Ruby on Rails向け為替レートAPI

require "net/http"
require "json"

class ExchangeRateClient
  Error = Class.new(StandardError)

  def convert(from:, to:, amount:)
    from = from.to_s.upcase
    to = to.to_s.upcase
    raise Error, "invalid currency code" unless [from, to].all? { |code| code.match?(/A[A-Z]{3}z/) }

    key = ["fx-convert", from, to, amount.to_d.to_s("F")]
    Rails.cache.fetch(key, expires_in: 60.seconds) do
      uri = URI("https://api.exchangerate.dev/v1/convert/#{from}/#{to}/#{amount}")
      request = Net::HTTP::Get.new(uri)
      request["Authorization"] = "Bearer #{ENV.fetch("EXCHANGERATE_API_KEY")}" 

      response = Net::HTTP.start(uri.host, uri.port, use_ssl: true,
        open_timeout: 2, read_timeout: 5) { |http| http.request(request) }
      raise Error, "exchange-rate API returned #{response.code}" unless response.is_a?(Net::HTTPSuccess)
      JSON.parse(response.body)
    end
  rescue Net::OpenTimeout, Net::ReadTimeout => error
    raise Error, "exchange-rate API timed out: #{error.class}"
  end
end

class ConversionsController < ApplicationController
  def show
    amount = BigDecimal(params.require(:amount))
    result = ExchangeRateClient.new.convert(
      from: params.require(:from).upcase,
      to: params.require(:to).upcase,
      amount: amount
    )
    render json: result.slice("from", "to", "amount", "rate", "converted",
      "source", "market_session", "data_updated_at")
  rescue ExchangeRateClient::Error, ArgumentError => error
    render json: { error: error.message }, status: :bad_gateway
  end
end