Extended Mind, Wikipedia Philosophy Checker inspired by http://xkcd.com/903 alt text

run.rb

#!/usr/bin/env ruby

# Extended Mind
# Wikipedia checker, the concept is that for any Wikipedia article you can
# eventually get to the article on Philosophy if you click the first link
# on the article.
# http://xkcd.com/903 (see alt text)

require 'open-uri'
require 'nokogiri'
require 'yaml'

class ExtendedMind

  def initialize
    @start_page  = ARGV[0]
    @breadcrumbs = []

    if File.exist?("./mind.cache")
      @cache = YAML.load_file("./mind.cache") || {}
    else
      @cache = {}
    end

    start
    crawl

    File.open("./mind.cache", "w") do |f|
      f.write(@cache.to_yaml)
    end

    print_results
  end

  def wikify(page)
    "http://wikipedia.org" + page
  end

  def unwikify(page)
    page.gsub("/wiki/", "")
  end

  def remove_bracket_links(text)
    temp = text
    first_bracket = temp.index "("
    last_bracket = temp.length - 1

    return temp if first_bracket.nil?

    done = false
    opening_brackets = 0
    (first_bracket..last_bracket).each do |index|
      if temp[index] == "("
        opening_brackets += 1
      elsif temp[index] == ")"
        opening_brackets -= 1
        if opening_brackets == 0
          last_bracket = index
          break
        end
      end
    end
    return temp if temp[last_bracket + 1] == '"' # First brackets might be within a valid link.
    temp[first_bracket..last_bracket] = ""
    return temp
  end

  def print_results
    puts "\n[-] Unable to check, recurses.\n" if @reached_end.nil?
    puts "[#{@breadcrumbs.length}] " + @breadcrumbs.map { |crumb| unwikify(crumb) }.join(" -> ")
  end

  def remove(elm)
    elm.remove
  end

  def get_pages_first_link(url)
    puts url
    return @cache[url] if @cache[url]
    page = Nokogiri::HTML(open(url))
    content = page.css("#bodyContent")

    # Remove invalid links.
    content.css(".dablink", ".navbox", ".tocolours", ".image").each(&:remove)
    content.css("p").first.inner_html = remove_bracket_links content.css("p").first.inner_html

    valid_links = content.css("p > a")
    if valid_links.empty?
      valid_links = content.css("ul > li > a")
    end
    @cache[url] = valid_links.first.attr("href")
  end

  def has_reached_end?
    return false if @breadcrumbs.length <= 2
    if @breadcrumbs.last == "/wiki/Philosophy"
      @reached_end = true
      return true
    end
    return @breadcrumbs[0..-2].include? @breadcrumbs.last
  end

  def add_crumb(url)
    @breadcrumbs << get_pages_first_link(wikify(url))
  end

  def start
    begin
      add_crumb("/wiki/#{@start_page}")
    rescue
      abort "Invalid start!"
    end
  end

  def crawl
    until has_reached_end?
      add_crumb(@breadcrumbs.last)
    end
  end

end

go = ExtendedMind.new

Excellent idea, this is now a repo if you wish to do a pull request. https://github.com/basicxman/extended-mind