Class: Exchanger::ExchangeRate

Inherits:
ActiveRecord::Base
  • Object
show all
Defined in:
lib/exchanger/exchange_rate.rb

Constant Summary collapse

DATA_SOURCE = 
"https://sdw.ecb.europa.eu/quickviewexport.do?SERIES_KEY=120.EXR.D.USD.EUR.SP00.A&type=csv".freeze
DATE_NORMALIZER = 
lambda { |date| Date.parse(date) rescue nil }

Class Method Summary collapse

Class Method Details

.exchange(amount:, dates:) ⇒ Object 



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# File 'lib/exchanger/exchange_rate.rb', line 64

def self.exchange(amount:, dates:)
  amount = amount.to_f
  dates = [*dates].map(&DATE_NORMALIZER)

  dates.map do |date|
    if date
      if rate_record = ExchangeRate.where(date: date).first
        # Regular business day, we have all the data.
        (rate_record.rate * amount).to_f
      elsif date.on_weekend? && next_business_day = skip_weekends(date.in_time_zone('Berlin').to_date, 1)
        # Weekends. When you send exchange request on a weekend, it will be exchanges on the next business day.
        # Note that this is in CET timezone as per ECB rules. Sorry, no luck exchanging on Moday from Sydney.

        # I wish I knew but I really don't
        return nil if next_business_day.future?

          rate_record = ExchangeRate.where(date: next_business_day).first
          (rate_record.rate * amount).to_f
      else
        # Sorry, don't know why you couldn't exchange euros on 2012-05-01. Sometimes ECB doesn't have data.
        # Also handles dates that are in future.
        "No rate for this date"
      end
    else
      "Invalid date passed"
    end
  end
end

.seed ⇒ Object

Seeds database with exchange rates from ECB.

As per www.ecb.europa.eu/stats/exchange/eurofxref/html/index.en.html, the reference rates are usually updated around 16:00 CET on every working day, except on TARGET closing days (holidays like Christmas). They are based on a regular daily concertation procedure between central banks across Europe, which normally takes place at 14:15 CET(but updates arounf 16pm)

We implement simplest possible caching based on ECD data update rules mentioned above.



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# File 'lib/exchanger/exchange_rate.rb', line 49

def self.seed
  last_available_record = ExchangeRate.order(:date).last

  if (last_available_record&.date == skip_weekends(Date.today.in_time_zone('Berlin').to_date, -1)) && Time.now.in_time_zone('Berlin').hour >= 16
    return
  end
  encoded_url = URI.encode(DATA_SOURCE)
  data = open(URI.parse(encoded_url)).read

  CSV.parse(data)[5..-1].each do |date, rate|
    next if rate == '-'
    ExchangeRate.find_or_create_by(date: date, rate: rate.to_f)
  end
end