aoc-2016-1.rb

require "set"

Command = Struct.new(:direction, :blocks)

class Compass
  BEARINGS = [:north, :east, :south, :west]

  def initialize
    @index = 0
  end

  def left
    if index == 0
      self.index = BEARINGS.length - 1
    else
      self.index -= 1
    end

    BEARINGS[self.index]
  end

  def right
    if index == BEARINGS.length - 1
      self.index = 0
    else
      self.index += 1
    end

    BEARINGS[self.index]
  end

  protected

  attr_accessor :index
end

pattern = /([LR])(\d+)/

commands = File.read("input.txt").split(", ").collect do |str|
  if str =~ pattern
    Command.new($1.to_sym, $2.to_i)
  else
    raise "nah bro"
  end
end

compass = Compass.new

visited_points = Set.new

current_point = [0,0]

commands.each do |command|
  bearing = case command.direction
    when :L then compass.left
    when :R then compass.right
    else raise ArgumentError, "Unknown direction"
  end

  axis_index = case bearing
    when :north, :south then 0
    when :east, :west then 1
  end

  operator = case bearing
    when :east, :south then :+
    when :west, :north then :-
  end

  # puts "turn #{command.direction}, now facing #{bearing}, move #{command.blocks} blocks"

  command.blocks.times do
    current_point[axis_index] = current_point[axis_index].public_send(operator, 1)
    puts "#{current_point}"

    if visited_points.include?(current_point)
      puts "visited twice! #{current_point.inspect}"
      puts current_point.collect(&:abs).inject(0, &:+)
      exit
    end

    visited_points << current_point
  end
end

puts current_point.inspect
puts current_point.collect(&:abs).inject(0, &:+)