Convert a FlyBuys card number to a barcode

convert-card-number-to-barcode.rb

#!/usr/bin/env ruby
# Convert a FlyBuys card number to a barcode

def get_check_sum_from_thirteen_digit_code(card_number)
  evens = 0
  odds = 0

  # Loop over all characters
  card_number.chars.each_with_index do |character, index|
    # Don't include the last character - 1
    break if index == card_number.length - 1

    # Convert to a number
    num = character.to_i

    if index.odd?
      evens += num
    else
      odds += num
    end
  end

  (10 - (((evens * 3) + odds) % 10)) % 10
end

def is_card_number_valid(card_number)
  # Implement your validation logic here
  true
end

def is_barcode_valid(barcode)
  return false unless barcode[0..2] == "264"
  return false unless barcode.length == 13
  return false unless barcode.chars.all? { |char| char =~ /[0-9]/ }
  return false unless is_checksum_valid(barcode)

  true
end

def is_checksum_valid(barcode)
  number_one = 0
  number_two = 0

  # Create number one
  (11).step(0, -2) do |i|
    char = barcode[i]
    val = char.to_i
    number_one += val
  end
  number_one *= 3

  # Create number two
  (0).step(12, 2) do |i|
    char = barcode[i]
    val = char.to_i
    number_two += val
  end
  number_two += number_one

  # Calculate the check digit
  check_digit = (10 - (number_two % 10)) % 10

  # Validate
  last_digit = barcode[12].to_i
  check_digit == last_digit
end

def convert_card_number_to_barcode(card_number)
  raise "Cannot convert an invalid card number to a barcode" unless is_card_number_valid(card_number)

  barcode = card_number[0..5].gsub(card_number[0..5], "264") + card_number[6..-1]
  check_sum = get_check_sum_from_thirteen_digit_code(barcode)

  # Update the last number with the checksum
  barcode = barcode[0..-2] + check_sum.to_s

  # Post condition validation
  raise "An invalid barcode was created from a card number" unless is_barcode_valid(barcode)

  barcode
end

puts convert_card_number_to_barcode(ARGV[0])