kaize/validates

class EanValidator < ActiveModel::EachValidator
  # http://en.wikipedia.org/wiki/International_Article_Number_(EAN)
  # EAN-8 & EAN-13 validator

  def validate_each(record, attribute, value)
    unless valid?(value)
      record.errors.add(attribute, :ean, options.merge(value: value))
    end
  end

  private

  def valid?(ean)
    return false if ean.blank?
    return false unless ean =~ /^\d+$/
    return false unless (8..13).include?(ean.length)
    return false unless calc_check_digit(ean)

    true
  end

  def calc_check_digit(ean)
    ean.rjust(13, "0".freeze).each_char.map.with_index { |char, i| char.to_i * EAN_CHECK_DIGIT13[i] }.reduce(:+) % 10 == 0
  end

  EAN_CHECK_DIGIT13 = [1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1, 3, 1]
  private_constant :EAN_CHECK_DIGIT13
end