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require 'mechanize'
require 'tsort'
##
# This example implements the alt-text of http://xkcd.com/903/ which states:
#
# Wikipedia trivia: if you take any article, click on the first link in the
# article text not in parentheses or italics, and then repeat, you will
# eventually end up at "Philosophy".
class WikipediaLinksToPhilosophy
def initialize
@agent = Mechanize.new
@agent.user_agent_alias = 'Mac Safari' # Wikipedia blocks "mechanize"
@history = @agent.history
@wiki_url = URI 'http://en.wikipedia.org'
@search_url = @wiki_url + '/w/index.php'
@random_url = @wiki_url + '/wiki/Special:Random'
@title = nil
@seen = nil
end
##
# Retrieves the title of the current page
def extract_title
@page.title =~ /(.*) - Wikipedia/
@title = $1
end
##
# Retrieves the initial page. If +query+ is not given a random page is
# chosen
def fetch_first_page query
if query then
search query
else
random
end
end
##
# The search is finished if we've seen the page before or we've reached
# Philosophy
def finished?
@seen or @title == 'Philosophy'
end
##
# Follows the first non-parenthetical, non-italic link in the main body of
# the article.
def follow_first_link
puts @title
# > p > a rejects italics
links = @page.root.css('.mw-content-ltr > p > a[href^="/wiki/"]')
# reject disambiguation and special pages, images and files
links = links.reject do |link_node|
link_node['href'] =~ %r%/wiki/\w+:|\(disambiguation\)%
end
links = links.reject do |link_node|
in_parenthetical? link_node
end
link = links.first
unless link then
# disambiguation page? try the first item in the list
link =
@page.root.css('.mw-content-ltr > ul > li > a[href^="/wiki/"]').first
end
# convert a Nokogiri HTML element back to a mechanize link
link = Mechanize::Page::Link.new link, @agent, @page
return if @seen = @agent.visited?(link)
@page = link.click
extract_title
end
##
# Is +link_node+ in an open parenthetical section?
def in_parenthetical? link_node
siblings = link_node.parent.children
seen = false
before = siblings.reject do |node|
seen or (seen = node == link_node)
end
preceding_text = before.map { |node| node.text }.join
open = preceding_text.count '('
close = preceding_text.count ')'
open > close
end
##
# Prints the result of the search
def print_result
if @seen then
puts "[Loop detected]"
else
puts @title
end
puts
# subtract initial search or Special:Random
puts "After #{@agent.history.length - 1} pages"
end
##
# Retrieves a random page from wikipedia
def random
@page = @agent.get @random_url
extract_title
end
##
# Entry point
def run query = nil
fetch_first_page query
follow_first_link until finished?
print_result
end
##
# Searches for +query+ on wikipedia
def search query
@page = @agent.get @search_url, search: query
extract_title
end
end
WikipediaLinksToPhilosophy.new.run ARGV.shift if $0 == __FILE__
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