Grid 4 - knights

#!/usr/bin/env ruby

class Matrix
  attr_reader :x_size, :y_size
  def initialize(x_size, y_size)
    @x_size = x_size
    @y_size = y_size
    @data = @y_size.times.map{|y| @x_size.times.map{|x| block_given? ? yield(x,y) : 0 } }
  end

  def [](x,y)
    @data[y % @y_size][x % @x_size]
  end

  def flatten
    @data.flatten
  end
end

class Grid
  def initialize(data)
    @x_size = data[0].size
    @y_size = data.size
    raise "Not a rectangle" unless data.all?{|row| row.size == @x_size}
    @data = Matrix.new(@x_size, @y_size){|x,y| data[y][x]}
  end

  def [](x,y)
    @data[x,y]
  end

  def knights(counts, val)
    Matrix.new(@x_size, @y_size) do |x,y|
      if self[x,y] == val
        counts[x+2,y+1] + counts[x+1,y+2] +
        counts[x+2,y-1] + counts[x+1,y-2] +
        counts[x-2,y+1] + counts[x-1,y+2] +
        counts[x-2,y-1] + counts[x-1,y-2]
      else
        0
      end
    end
  end

  def run!
    counts_1 = Matrix.new(@x_size, @y_size) do |x,y|
      if self[x,y] == "1"
        1
      else
        0
      end
    end
    counts_12 = knights(counts_1, "2")
    counts_123 = knights(counts_12, "3")
    counts_1234 = knights(counts_123, "4")
    p counts_1234.flatten.inject(&:+)
  end
end

grid = Grid.new(open("grid4.txt").read.split("\n"))
grid.run!