Say a number string in English

say_number_str.rb

THOUSANDS = ['', 'thousand', 'million', 'billion']
NUMS = {
  "0"   => '',
  "1"   => 'one',
  "2"   => 'two',
  "3"   => 'three',
  "4"   => 'four',
  "5"   => 'five',
  "6"   => 'six',
  "7"   => 'seven',
  "8"   => 'eight',
  "9"   => 'nine',
  "10"  => 'ten',
  "11"  => 'eleven',
  "12"  => 'twelve',
  "13"  => 'thirteen',
  "14"  => 'fourteen',
  "15"  => 'fifteen',
  "16"  => 'sixteen',
  "17"  => 'seventeen',
  "18"  => 'eighteen',
  "19"  => 'nineteen',
  "20"  => 'twenty',
  "30"  => 'thirty',
  "40"  => 'fourty',
  "50"  => 'fifty',
  "60"  => 'sixty',
  "70"  => 'seventy',
  "80"  => 'eighty',
  "90"  => 'ninty'
}

def say_thousand(str)
  return "" if str.empty?

  if NUMS[str]
    return NUMS[str]
  elsif str.size == 3
    if str[0..0] == "0"
      return say_thousand(str[1..-1])
    else
      return NUMS[str[0..0]] + " hundred " + say_thousand(str[1..-1])
    end
  else
    if str[0..0] == "0"
      return say_thousand(str[1..-1])
    else
      return "#{NUMS[str[0..0] + "0"]} " + say_thousand(str[1..-1])
    end
  end
end

def split_thousand(str)
  length = str.size
  thousands = []
  num_leading_digits = length % 3
  leading_digits = str[0...num_leading_digits]
  thousands << leading_digits unless leading_digits.empty?
  thousands + str[num_leading_digits..-1].scan(/.{3}/)
end

def say(str)
  return "zero" if str == '0'

  result = ""
  thousands = split_thousand(str)
  (0..(thousands.size - 1)).each do |i|
    result += say_thousand(thousands[i]) + " #{THOUSANDS[thousands.size - 1 - i]} "
  end

  return result
end

puts say("90501")
puts say("9999999")
puts say("1293871985")