Luhn Checksum implementation

luhn.rb

#!/usr/bin/env ruby

# longer version with project structure and specs at https://github.com/jmeridth/luhn

require 'optparse'
      
def help
  puts "Usage: luhn [positive number to validate]"
end
        
options = {}
opts = OptionParser.new do |opts|
  opts.banner = "Luhn Checksum implementation"
        
  opts.on("-h","-?","--help", "Display help") do
    help
    exit 0
  end
end 
      
begin 
  opts.parse!
rescue OptionParser::InvalidOption => e
  help
  exit 1
end

if ARGV.size != 1
  help
  exit 1
end

module Luhn
  class CLI
    def self.is_valid?(number)
      odds = evens = 0
      number.to_s.reverse.chars.each_slice(2) do |odd,even|
        odds += odd.to_i

        double = even.to_i * 2
        if double >= 10
          double = double.to_s.chars.map(&:to_i).inject(:+)
        end
        evens += double
      end
      (odds + evens) % 10 == 0
    end
    
    def self.run(number)
      puts "With an input of #{number} the output would be:"
      puts "#{number} is #{self.is_valid?(number) && 'valid' ||'not valid'}"
    end
  end
end

Luhn::CLI.run(ARGV[0])