Ruby implementation of the common code exercise

toy_robot.rb

require "matrix"
require "readline"

class ToyRobot
  PROMPT  = "> "
  PLACE   = /\APLACE\s+(\d+),(\d+),(NORTH|SOUTH|EAST|WEST)\z/
  COMMAND = /\ALEFT|RIGHT|MOVE|REPORT\z/
  QUIT    = /\AQUIT\z/
  LEFT    = Matrix[[0,  1], [-1, 0]]
  RIGHT   = Matrix[[0, -1], [ 1, 0]]

  FACING = {
    "NORTH" => Matrix[[ 0,  1]], "SOUTH" => Matrix[[ 0, -1]],
    "EAST"  => Matrix[[ 1,  0]], "WEST"  => Matrix[[-1,  0]]
  }

  class << self
    def run
      new.run
    end
  end

  def initialize(width: 5, height: 5)
    @width, @height = height, width
    @position = @direction = nil
  end

  def run
    begin
      while (input = Readline.readline(PROMPT, true))
        command(input)
      end
    rescue Interrupt
      exit
    end
  end

  private

  def placed?
    @position && @direction
  end

  def valid?(position = @position + @direction)
    position[0, 0].between?(0, @width) && position[0, 1].between?(0, @height)
  end

  def place(position, direction)
    if valid?(position)
      @position, @direction = position, direction
    end
  end

  def left
    @direction *= LEFT
  end

  def right
    @direction *= RIGHT
  end

  def move
    @position += @direction if valid?
  end

  def report
    puts "= #{@position[0, 0]},#{@position[0, 1]},#{FACING.key(@direction)}"
  end

  def command(input)
    case input
    when COMMAND
      send input.downcase.to_sym if placed?
    when PLACE
      place Matrix[[$1.to_i, $2.to_i]], FACING[$3]
    when QUIT
      quit
    end
  end

  def quit
    exit
  end
end

ToyRobot.run