fmtnum

#!/usr/bin/env ruby
# tlehman
# 
#   Usage:
#     $ fmtnum "$(echo 7^7^2 | bc)"
#     256,923,577,521,058,878,088,611,477,224,235,621,321,607
#
#     $ echo 7^7^2 | bc | fmtnum
#     256,923,577,521,058,878,088,611,477,224,235,621,321,607

DIGITS = %w{one two three four five six seven eight nine ten}

BIG_NUMBERS = {
  2 => 'hundred',
  3 => 'thousand',
  6 => 'million',
  9 => 'billion',
  12 => 'trillion',
  15 => 'quadrillion',
  18 => 'quintillion',
  21 => 'sextillion',
  24 => 'septillion',
  27 => 'octillion',
  30 => 'nonillion',
  33 => 'decillion',
  36 => 'undecillion',
  39 => 'duodecillion',
  42 => 'tredecillion',
  45 => 'quattuordecillion',
  48 => 'quindecillion',
  51 => 'sexdecillion',
  54 => 'septendecillion',
  57 => 'octodecillion',
  60 => 'novemdecillion',
  63 => 'vigintillion',
  66 => 'unvigintillion',
  69 => 'duovigintillion',
  72 => 'trevigintillion',
  75 => 'quattuorvigintillion',
  78 => 'quinvigintillion',
  81 => 'sexvigintillion',
  84 => 'septenvigintillion',
  87 => 'octovigintillion',
  90 => 'novemvigintillion',
  93 => 'trigintillion',
  96 => 'untrigintillion',
  99 => 'duotrigintillion',
  100 => 'googol'
}

def usage
<<-EOF
Usage:
  $ fmtnum 20100102030304
  20,100,102,030,304
EOF
end

def number?(input)
  !input.nil? && (input =~ /^(\d+)(\.\d+)?$/)
end

def format(n)
  n.gsub(/(?<=\d)(?=(\d\d\d)+(\b|\.))/, ',')
end

input = ARGV.first
input = STDIN.read if input.nil?

if number?(input)
  puts format(input)
else 
  puts usage
end