module UcStudentNumber

# File lib/uc_student_number.rb, line 5
def self.validate(number)
  return false if !number || number.to_s.length < 7
  number = number.to_s.strip
  given_digits = number.reverse[1..-1].split('').map(&:to_i)
  given_verification = number.reverse[0].upcase
  get_verification_digit(given_digits) == given_verification
end

# File lib/uc_student_number.rb, line 13
def self.get_verification_digit(digits)
  counter = 2
  sum = 0
  digits.each do |digit|
    sum += (digit * counter)
    counter += 1
    counter = counter > 8 ? 2 : counter
  end

  ((11 - sum) % 11 != 10) ? ((11 - sum) % 11).to_s : 'J'
end