require "spec_helper"

describe "problem eight" do
  #The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

  let(:data) do
    <<-BLAH
    73167176531330624919225119674426574742355349194934
    96983520312774506326239578318016984801869478851843
    85861560789112949495459501737958331952853208805511
    12540698747158523863050715693290963295227443043557
    66896648950445244523161731856403098711121722383113
    62229893423380308135336276614282806444486645238749
    30358907296290491560440772390713810515859307960866
    70172427121883998797908792274921901699720888093776
    65727333001053367881220235421809751254540594752243
    52584907711670556013604839586446706324415722155397
    53697817977846174064955149290862569321978468622482
    83972241375657056057490261407972968652414535100474
    82166370484403199890008895243450658541227588666881
    16427171479924442928230863465674813919123162824586
    17866458359124566529476545682848912883142607690042
    24219022671055626321111109370544217506941658960408
    07198403850962455444362981230987879927244284909188
    84580156166097919133875499200524063689912560717606
    05886116467109405077541002256983155200055935729725
    71636269561882670428252483600823257530420752963450
    BLAH
  end

  #Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
  class MassScan
    attr_accessor :data

    def initialize(data)
      @data = data.gsub(/ /, '').gsub(/\n/, '')
      @position = 0
    end

    def scan(digits: 4)
      queue = []
      max = 0

      until @position > @data.size
        fill(queue, digits)
        result = product(queue)
        if result > max
          max_queue = queue.dup
          max = result
          puts [max, max_queue].inspect
        end
      end

      max
    end

    private

    def fill(queue, size)
      available_room = size - queue.size
      if available_room == 0
        queue.shift
        available_room = 1
      end
      available_room.times do |n|
        queue.push(data[@position])
        @position = @position + 1
      end
    end

    def product(queue)
      queue.inject(1) do |memo, n|
        memo *= n.to_i
      end
    end
  end

  subject { MassScan.new(data) }

  it "returns the four digits that produce the greatest product" do
    expect(subject.scan(digits: 4)).to eql(5832)
  end

  it "returns the thirteen digits that produce the greatest product" do
    expect(subject.scan(digits: 13)).to eql(23514624000)
  end
end