module CouponCode

# File lib/coupon_code.rb, line 35
def self.checkdigit_alg_1(orig, check)
  orig.split('').each_with_index do |c, _|
    k = SYMBOL.index(c)
    check = check * 19 + k
  end
  SYMBOL[check % 31]
end

# File lib/coupon_code.rb, line 10
def self.generate(options = { parts: PARTS })
  num_parts = options.delete(:parts)
  parts = []
  (1..num_parts).each do |i|
    part = ''
    (1...LENGTH).each { part << random_symbol }
    part << checkdigit_alg_1(part, i)
    parts << part
  end
  parts.join('-')
end

# File lib/coupon_code.rb, line 43
def self.random_symbol
  SYMBOL[rand(SYMBOL.length)]
end

# File lib/coupon_code.rb, line 22
def self.validate(orig, num_parts = PARTS)
  code = orig.upcase
  code.gsub!(/[^#{SYMBOL}]+/, '')
  parts = code.scan(/[#{SYMBOL}]{#{LENGTH}}/)
  return if parts.length != num_parts
  parts.each_with_index do |part, i|
    data  = part[0...(LENGTH - 1)]
    check = part[-1]
    return if check != checkdigit_alg_1(data, i + 1)
  end
  parts.join('-')
end