ISBN13 barcode check digit

isbn13barcode

module IsbnCalculator
	def self.isbn(num)
		total = multiply_by(num, 1, 3) 
		mod_val = total % 10
		mod_val = 10 - mod_val
		final_val = mod_val == 10 ? 0 : mod_val
		num.to_s + final_val.to_s
	end


	def self.multiply_by(num, first, second)
		tot = 0
		 num.to_s.split("").each_with_index do |n, index|
		  if index.even?
			tot += (n.to_i*first.to_i)
		  else
		   tot += (n.to_i*second.to_i)
		  end
		end
	   tot
	end
end


puts "Type a number to calculate check digit of an ISBN13 barcode"
num = gets.chomp
puts "The isbn13 check digit is"
puts IsbnCalculator::isbn(num)