board.rb

class Board
  def initialize(n)
    @n = n
    @board = []
    (0...@n).each { |i| @board << Array.new(@n, 'x') }
    @x = 0
    @y = 0
    @color = "R"
    @direction = :right
    @colored_positions = 0

    print_board
    nada = gets
  end

  def run!
    while @colored_positions < (@n * @n) do
      colorize
      change_position

      print_board
      nada = gets
    end
  end

  def change_position
    temp_x = @x
    temp_y = @y

    next_position

    unless valid_position?
      puts "nao eh valida"
      @x = temp_x
      @y = temp_y

      change_direction
      next_position
    end

    puts "#{@x}, #{@y}"
  end

  def valid_position?
    @x >= 0 && @x < @n && @y >= 0 && @y < @n && @board[@x][@y] == 'x'
  end

  def change_direction
    case @direction
      when :right then @direction = :down
      when :down then @direction = :left
      when :left then @direction = :up
      when :up then @direction = :right
    end
  end

  def change_color
    case @color
      when 'R' then @color = 'G'
      when 'G' then @color = 'B'
      when 'B' then @color = 'R'
    end
  end

  def next_position
    case @direction
      when :right then @y += 1
      when :left then @y -= 1
      when :down then @x += 1
      when :up then @x -= 1
    end
  end

  def colorize
    @board[@x][@y] = @color
    change_color
    @colored_positions += 1
  end

  def print_board
    puts "=========================="
    @board.each do |line|
      puts line.join(" ")
    end
  end
end

Board.new(5).run!