roman numerals after Sandi Metz

roman_numerals.rb

# frozen_string_literal: false
# module that refines String and Numeric
module Roman
  refine Fixnum do
    def to_roman
      RomanNumerals.new.to_s(self)
    end
  end

  refine String do
    def to_subtractive_roman
      RomanNumeralConversion.new(self).to_subtractive
    end

    def to_additive_roman
      RomanNumeralConversion.new(self).to_additive
    end

    alias_method :to_i_orig, :to_i
    def to_i(type = nil)
      type == :roman ? RomanNumerals.new.to_i(self) : to_i_orig
    end
  end
end

using Roman

# to Roman numeral class
class RomanNumerals
  KEY = [1_000, 500, 100, 50, 10, 5, 1]
  ROMAN = %w(M D C L X V I)
  ROMAN_NUMERALS = KEY.zip(ROMAN).to_h

  def to_s(num)
    to_roman(num)
  end

  def to_i(str)
    to_number(str)
  end

  def to_roman(number)
    result = ''
    ROMAN_NUMERALS.keys.reduce(number) do |to_be_converted, base_10_value|
      num_chars_needed, remainder = to_be_converted.divmod(base_10_value)
      result << ROMAN_NUMERALS[base_10_value] * num_chars_needed
      remainder
    end
    result.to_subtractive_roman
  end

  def to_number(roman)
    roman.to_additive_roman.chars.reduce(0) do |total, roman_letter|
      total + ROMAN_NUMERALS.invert[roman_letter]
    end
  end
end

# from Roman numeral conversion class
class RomanNumeralConversion
  LONG = %w(DCCCC CCCC LXXXX XXXX VIIII IIII)
  SHORT = %w(CM CD XC XL IX IV)
  LONG_TO_SHORT_MAP = LONG.zip(SHORT).to_h

  attr_reader :roman
  def initialize(roman)
    @roman = roman
  end

  def to_additive
    convert(LONG_TO_SHORT_MAP.invert)
  end

  def to_subtractive
    convert(LONG_TO_SHORT_MAP)
  end

  def convert(map)
    map.keys.reduce(roman) do |converted_roman, alternate_form|
      converted_roman.gsub(/#{alternate_form}/, map[alternate_form])
    end
  end
end

# For the Sandi Metz original sign up to her 99 bottle mailing list
# http://sandimetz.us3.list-manage.com/track/click?u=1090565ccff48ac602d0a84b4&id=bd938590a4&e=8144e160c6

roman_numerals_test.rb

# frozen_string_literal: false

#!/usr/bin/env ruby
gem 'minitest', '>= 5.0.0'
require 'minitest/autorun'
require 'minitest/pride'
require_relative 'roman_numerals'

using Roman

# the test
class RomanNumeralsTest < Minitest::Test
  attr_reader :integers
  def setup
    integer = [1, 4, 7, 11, 19, 49, 54, 99, 899, 999]
    roman = %w(I IV VII XI XIX XLIX LIV XCIX DCCCXCIX CMXCIX)
    @integers = integer.zip(roman)
  end
  
  def test_to_roman
    integers.each do |pair|
      assert_equal pair[1], pair[0].to_roman
    end
  end

  def test_to_arabic
    integers.each do |pair|
      assert_equal pair[0], pair[1].to_i(:roman)
    end
  end
end

# the long to short test
class RomanNumeralConversionTest < Minitest::Test
  def test_2
    assert_equal 'II', RomanNumeralConversion.new('II').to_subtractive
    assert_equal 'II', RomanNumeralConversion.new('II').to_additive
  end

  def test_4
    assert_equal 'IV', RomanNumeralConversion.new('IIII').to_subtractive
    assert_equal 'IIII', RomanNumeralConversion.new('IV').to_additive
  end

  def test_9
    assert_equal 'IX', RomanNumeralConversion.new('VIIII').to_subtractive
    assert_equal 'VIIII', RomanNumeralConversion.new('IX').to_additive
  end

  def test_49
    assert_equal 'XLIX', RomanNumeralConversion.new('XXXXVIIII').to_subtractive
    assert_equal 'XXXXVIIII', RomanNumeralConversion.new('XLIX').to_additive
  end

  def test_99
    assert_equal 'XCIX', RomanNumeralConversion.new('LXXXXVIIII').to_subtractive
    assert_equal 'LXXXXVIIII', RomanNumeralConversion.new('XCIX').to_additive
  end

  def test_449
    assert_equal 'CDXLIX', RomanNumeralConversion.new('CCCCXXXXVIIII').to_subtractive
    assert_equal 'CCCCXXXXVIIII', RomanNumeralConversion.new('CDXLIX').to_additive
  end

  def test_999
    assert_equal 'XCIX', RomanNumeralConversion.new('LXXXXVIIII').to_subtractive
    assert_equal 'LXXXXVIIII', RomanNumeralConversion.new('XCIX').to_additive
  end
end