Converts a Double to Natural Language

convert.rb

class Convert
  def self.to_string(double)
    split = double.to_s.split('.')
    # Tack the tens on to cents if not present (.90 => .9 for example)
    split[1] << "0" if split[1] and split[1].length == 1

    dollars = convert(split[0])
    cents = convert(split[1])

    dollars = plural(dollars, 'Dollar', split[0]) if dollars
    cents = plural(cents, 'Cent', split[1]) if cents

    return "Free" unless dollars or cents
    return dollars unless cents
    return cents unless dollars
    return "#{dollars} and #{cents}"
  end

  private
  def self.convert(digit)
    return nil if !digit or digit == "0"
    build = digitToWords(digit)
    build = insertPlaceNames(build)
    build = compileGroups(build)
    build.join(', ').strip
  end

  def self.plural words, word, digit
    word << "s" if digit.to_i > 1
    "#{words} #{word}"
  end

  def self.insertPlaceNames(build)
    build.map! do |group|
      if group.select { |digit| !!digit }.length == 0
        nil
      else
        group
      end
    end

    build.each_index do |idx|
      next unless build[idx]
      # Handle the actual place name (for thousands and up)
      build[idx] << "#{build[idx].pop} #{placeName(build.length - idx)}" unless (idx == build.length - 1)
      # Handle the hundred spot for this group
      build[idx].unshift "#{build[idx].shift} #{placeName(1)}" if build[idx].length == 3
    end
    build
  end

  def self.placeName(place)
    return nil if place == 0
    return "Hundred" if place == 1
    return "Thousand" if place == 2
    return "Million" if place == 3
    return "Billion" if place == 4
    return "Trillion" if place == 5
  end

  def self.compileGroups(build)
    build.select { |g| !!g }.map do |group|
      group = group.select { |w| w }
      if group.length > 1
        group << [group.pop, group.pop].reverse.join('-')
      end
      group.join(' and ')
    end
  end

  def self.digitToWords(digit)
    build = []
    groups = (digit.length / 3.0).ceil - 1

    groups.downto(0).each do |g|
      words = []
      group = digit.reverse[g * 3, 3].reverse

      # Shortcircuit single digits
      if group.length == 1
        words << wordSingle(group)
        build << words
        next
      end

      # Handle the thousands
      if group.length == 3
        words << wordSingle(group[0,1])
        group = group[1,2]
      end

      # Now we know we have a tens group left
      if group.start_with? "1"
        words << wordSingleTen(group)
      else
        words << wordTen(group[0,1])
        words << wordSingle(group[1,1])
      end

      build << words
    end

    build
  end

  def self.wordSingle(digit)
    return nil if digit == "0"
    return "One" if digit == "1"
    return "Two" if digit == "2"
    return "Three" if digit == "3"
    return "Four" if digit == "4"
    return "Five" if digit == "5"
    return "Six" if digit == "6"
    return "Seven" if digit == "7"
    return "Eight" if digit == "8"
    return "Nine" if digit == "9"
  end

  def self.wordTen(digit)
    return nil if digit == "0"
    return "Ten" if digit == "1"
    return "Twenty" if digit == "2"
    return "Thirty" if digit == "3"
    return "Fourty" if digit == "4"
    return "Fifty" if digit == "5"
    return "Sixty" if digit == "6"
    return "Seventy" if digit == "7"
    return "Eighty" if digit == "8"
    return "Ninety" if digit == "9"
  end

  def self.wordSingleTen(digit)
    return "Ten" if digit == "10"
    return "Eleven" if digit == "11"
    return "Twelve" if digit == "12"
    return "Thirteen" if digit == "13"
    return "Fourteen" if digit == "14"
    return "Fifteen" if digit == "15"
    return "Sixteen" if digit == "16"
    return "Seventeen" if digit == "17"
    return "Eighteen" if digit == "18"
    return "Nineteen" if digit == "19"
  end
end

convert_spec.rb

require 'convert'

describe Convert do
  describe "to_string" do
    it "should convert doubles to word form" do
      Convert.to_string(10000).should == "Ten Thousand Dollars"
      Convert.to_string(0.01).should == "One Cent"
      Convert.to_string(0.12).should == "Twelve Cents"
      Convert.to_string(1.23).should == "One Dollar and Twenty-Three Cents"
      Convert.to_string(12.34).should == "Twelve Dollars and Thirty-Four Cents"
      Convert.to_string(123.45).should == "One Hundred and Twenty-Three Dollars and Fourty-Five Cents"
      Convert.to_string(1234.56).should == "One Thousand, Two Hundred and Thirty-Four Dollars and Fifty-Six Cents"
      Convert.to_string(12345.67).should == "Twelve Thousand, Three Hundred and Fourty-Five Dollars and Sixty-Seven Cents"
      Convert.to_string(123456.78).should == "One Hundred and Twenty-Three Thousand, Four Hundred and Fifty-Six Dollars and Seventy-Eight Cents"
      Convert.to_string(1234567.89).should == "One Million, Two Hundred and Thirty-Four Thousand, Five Hundred and Sixty-Seven Dollars and Eighty-Nine Cents"
      Convert.to_string(12345678.90).should == "Twelve Million, Three Hundred and Fourty-Five Thousand, Six Hundred and Seventy-Eight Dollars and Ninety Cents"
      Convert.to_string(999999999999.99).should == "Nine Hundred and Ninety-Nine Billion, Nine Hundred and Ninety-Nine Million, Nine Hundred and Ninety-Nine Thousand, Nine Hundred and Ninety-Nine Dollars and Ninety-Nine Cents"
    end
  end
end