require 'project_euler/problem_base'

module ProjectEuler
  # Solution to problem #011.
  class Problem011 < ProblemBase
    GRID = %w(
      08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
      49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
      81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65
      52 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 91
      22 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 80
      24 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 50
      32 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 70
      67 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 21
      24 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 72
      21 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 95
      78 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 92
      16 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 57
      86 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 58
      19 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 40
      04 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 66
      88 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 69
      04 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 36
      20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
      20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
      01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
    ).each_slice(20).map { |a| a.map(&:to_i) }

    def self.answer
      new.answer
    end

    def answer
      [horizontal_max, vertical_max, diagonal_max].max
    end

    private

    def horizontal_max
      row_max(GRID)
    end

    def vertical_max
      row_max(GRID.transpose)
    end

    def row_max(grid)
      grid.map { |row|
        row.each_cons(4).map { |cons| cons.inject(1, :*) }.max
      }.max
    end

    def diagonal_max
      [diagonal_max_ltr, diagonal_max_rtl].max
    end

    def diagonal_max_ltr
      0.upto(16).map { |row|
        0.upto(16).map { |col|
          0.upto(3).map { |offset|
            GRID[row + offset][col + offset]
          }.inject(1, :*)
        }.max
      }.max
    end

    def diagonal_max_rtl
      0.upto(16).map { |row|
        3.upto(19).map { |col|
          0.upto(3).map { |offset|
            GRID[row + offset][col - offset]
          }.inject(1, :*)
        }.max
      }.max
    end
  end
end
