additive_function_validator.rb

#!/usr/bin/env ruby

require 'prime'

class AdditiveFunctionValidator

  attr_reader :limit, :prime_numbers

  def initialize(limit:)
    @limit = limit
  end

  def secret(input_integer)
    input_integer
  end

  def prime_numbers
    @prime_numbers ||= Prime.take_while {|p| p < limit }
  end

  def additive?(x, y)
    secret(x + y) == secret(x) + secret(y)
  end

  def additive_for_prime_numbers?
    visited = []

    prime_numbers.each do |x|
      prime_numbers.each do |y|
        break if visited.include?(y)
        return false unless additive?(x, y)
      end
      visited << x
    end

    return true
  end
end


if ARGV.empty?
  puts "Integer argument is required"
else
  input_integer = ARGV[0].to_i
  additive_function_validator = AdditiveFunctionValidator.new(limit: input_integer)

  if additive_function_validator.additive_for_prime_numbers?
    puts 'secret() is additive for all prime numbers under %s.' % input_integer
  else
    puts 'secret() is not additive for all prime numbers under %s.' % input_integer
  end
end