require 'simple_validation'

class AlienNumber
  include SimpleValidation

  validate :digits_are_positive
  validate :digits_are_less_than_ten, :if => [:digits_count_even?]

  def initialize(*digits)
    @digits = digits
  end

  def value
    @digits.reduce(0) {|result, digit| result + digit}
  end

  private

  def digits_are_positive
    @digits.each do |digit|
      add_error("#{digit} is negative") unless digit > 0
    end
  end

  def digits_are_less_than_ten
    @digits.each do |digit|
      add_error("#{digit} is greater than 9") unless digit < 10
    end
  end

  def digits_count_even?
    @digits.size.even?
  end
end

valid_number = AlienNumber.new(1, 2, 3)
valid_number.valid? # true
valid_number.invalid? # false
valid_number.errors # []
valid_number.value # 6

invalid_number = AlienNumber.new(-1, 12)
invalid_number.valid? # false
invalid_number.invalid? # true
invalid_number.errors # ["-1 is negative", "12 is greater than 9"]
invalid_number.value # 11

another_invalid_number = AlienNumber.new(-10, 12, 15)
another_invalid_number.valid? # false
another_invalid_number.invalid? # true
another_invalid_number.errors # ["-10 is negative"]
another_invalid_number.value # 17