frankfurter/lib/snapshot.rb

require_relative 'db'

class Snapshot
  def self.last
    new Currency.last_date
  end

  def initialize(date)
    @date = date
  end

  def to_base(base)
    rebased_rates = rates

    unless base == 'EUR'
      base_rate = rebased_rates
        .update('EUR' => 1.0)
        .delete base

      rebased_rates.each do |iso_code, rate|
        new_rate = rate / base_rate
        rebased_rates[iso_code] =
          case new_rate
          when new_rate > 100
            new_rate.round 2
          when new_rate > 10
            new_rate.round 3
          else
            new_rate.round 4
          end
      end
    end

    {
      base:  base,
      date:  @date,
      rates: rebased_rates
    }
  end

  private

  def rates
    Currency
      .where(date: @date)
      .reduce({}) { |hsh, currency|
        hsh.update currency.to_hash
      }
  end
end