Lucky Numbers

lucky_numbers.rb

class LuckyNumbers
  attr_accessor :lucky_number
  LUCKY_NUMBER = 7
  INTERVAL = 9

  def initialize(min = 0)
    @lucky_number = min.to_i - 1
  end

  def lucky?(number)
    sum = number
    loop_times(number).times { sum = sum_digits(sum) }
    sum == LUCKY_NUMBER
  end

  def numbers
    Enumerator.new do |yielder|
      loop do
        self.lucky_number += 1
        yielder.yield(lucky_number) if lucky?(lucky_number)
      end
    end
  end

  private

  def sum_digits(number)
    number.digits.sum
  end

  def loop_times(number)
    number.digits.select { |l| !l.zero? }.length
  end
end

lucky_numbers = LuckyNumbers.new(ARGV[0]).numbers

loop do
  lucky_number = lucky_numbers.next
  $stdout.puts lucky_number
  break if lucky_number + (LuckyNumbers::INTERVAL - 1) > ARGV[1].to_i
end

lucky_numbers_spec.rb

require_relative 'lucky_numbers'

describe LuckyNumbers do
  let!(:min) { 100 }
  let!(:lucky_numbers) { described_class.new(min) }

  describe '#initialize' do
    it 'sets lucky_number instance variable to one number less than min arg' do
      expect(lucky_numbers.lucky_number).to eq(min - 1)
    end
  end

  describe '#is_lucky?' do
    it 'returns true when a number is lucky' do
      num = 62_431
      expect(lucky_numbers.lucky?(num)).to be true
      num2 = 2_298_193_999_999_999_999_999_999_999_999_999_999_999_999_999_998_984_398_249_328_493_829_489_238_982_394_823_948_392_489_489_384_394_894_392_893_274_923_748_923_748_937_248_973_289_473_298_479_828_329_748_937_489_735
      expect(lucky_numbers.lucky?(num2)).to be true
    end

    it 'returns false when a number is not lucky' do
      num = 62_432
      expect(lucky_numbers.lucky?(num)).to be false
    end
  end

  describe '#numbers' do
    it 'returns an enumerator' do
      expect(lucky_numbers.numbers).to be_an Enumerator
    end

    it 'responds to next' do
      expect(lucky_numbers.lucky_number).to_not eq(106)
      expect(lucky_numbers.numbers.next).to eq(106)
    end

    it 'updates the @lucky_number instance variable' do
      lucky_numbers.numbers.next
      expect(lucky_numbers.lucky_number).to eq(106)
      lucky_numbers.numbers.next
      expect(lucky_numbers.lucky_number).to eq(115)
    end
  end
end