Maybe/app/models/provider/synth.rb

class Provider::Synth
  include Retryable

  def initialize(api_key)
    @api_key = api_key
  end

  def fetch_security_prices(ticker:, start_date:, end_date:)
    prices = paginate(
      "#{base_url}/tickers/#{ticker}/open-close",
      start_date: start_date,
      end_date: end_date
    ) do |body|
      body.dig("prices").map do |price|
        {
          date: price.dig("date"),
          price: price.dig("close")&.to_f || price.dig("open")&.to_f,
          currency: "USD"
        }
      end
    end

    SecurityPriceResponse.new \
      prices: prices,
      success?: true,
      raw_response: prices.to_json
  rescue StandardError => error
    SecurityPriceResponse.new \
      success?: false,
      error: error,
      raw_response: error
  end

  def fetch_exchange_rate(from:, to:, date:)
    retrying Provider::Base.known_transient_errors do |on_last_attempt|
      response = Faraday.get("#{base_url}/rates/historical") do |req|
        req.headers["Authorization"] = "Bearer #{api_key}"
        req.params["date"] = date.to_s
        req.params["from"] = from
        req.params["to"] = to
      end

      if response.success?
        ExchangeRateResponse.new \
          rate: JSON.parse(response.body).dig("data", "rates", to),
          success?: true,
          raw_response: response
      else
        if on_last_attempt
          ExchangeRateResponse.new \
            success?: false,
            error: build_error(response),
            raw_response: response
        else
          raise build_error(response)
        end
      end
    end
  end

  private

    attr_reader :api_key

    ExchangeRateResponse = Struct.new :rate, :success?, :error, :raw_response, keyword_init: true
    SecurityPriceResponse = Struct.new :prices, :success?, :error, :raw_response, keyword_init: true

    def base_url
      "https://api.synthfinance.com"
    end

    def build_error(response)
      Provider::Base::ProviderError.new(<<~ERROR)
        Failed to fetch data from #{self.class}
          Status: #{response.status}
          Body: #{response.body.inspect}
      ERROR
    end

    def fetch_page(url, page, params = {})
      Faraday.get(url) do |req|
        req.headers["Authorization"] = "Bearer #{api_key}"
        params.each { |k, v| req.params[k.to_s] = v.to_s }
        req.params["page"] = page
      end
    end

    def paginate(url, params = {})
      results = []
      page = 1
      current_page = 0
      total_pages = 1

      while current_page < total_pages
        response = fetch_page(url, page, params)

        if response.success?
          body = JSON.parse(response.body)
          page_results = yield(body)
          results.concat(page_results)

          current_page = body.dig("paging", "current_page")
          total_pages = body.dig("paging", "total_pages")

          page += 1
        else
          raise build_error(response)
        end
      end

      results
    end
end