luhn.rb

module Luhn
	def self.is_valid?(number)


		# ----------------------------------------------------
		#
		# line 17  - take the number, convert it to a string 
		# and reverse it. '.chars' splits it by digit, then
		# '.map' combined with (&:to_i) converts it to an integer. 
		#
		# line 18 - 'sum' serves as a variable to push the numbers 
		# to once they are doubled / subtracted from, unless they're 
		# odd, in which case they are added to the variable as is.

		reversedNums = number.to_s.reverse.chars.map(&:to_i)
  	sum = 0

  	# ----------------------------------------------------

  	# ----------------------------------------------------
  	#
  	# line 32 - I need clarification on this. 
  	#
  	# lines 33 - 35 add the numbers to sum, unless their 
  	# position in the array is even, in which case they're 
  	# multiplied by two.
  	# 
  	# line 36 - I need clarification on this. 

  	reversedNums.each_slice(2) do |odd, even|
    sum += odd
    next unless even
    even *= 2
    even = even.divmod(10).inject(:+) if even > 9
    sum += even
  end

  return sum.modulo(10) == 0
			
	end	
end