class CreditCardChecker

# File lib/credit_card_checker.rb, line 2
def self.valid?(str)
  return false if /[^\d\s]/.match(str)

  arr = str.split(' ').join('').split('')
  return false if arr.length < 2

  sum = 0
  startIndex = 1
  startIndex = 0 if arr.length.even?
  endIndex = arr.length - 2
  (startIndex..endIndex).step(2).each do |index|
    d = arr[index].to_i
    sum += if d * 2 > 9
             d * 2 - 9
           else
             d * 2
           end
  end
  startIndex = 0
  startIndex = 1 if arr.length.even?
  endIndex = arr.length - 1
  (startIndex..endIndex).step(2).each do |index|
    d = arr[index].to_i
    sum += d
  end
  sum % 10 == 0
end