Path to Philosophy

#!/usr/bin/env ruby

require 'open-uri'
require 'nokogiri'

base_url = 'https://en.wikipedia.org'
site = ARGV.empty? ? 'Film_adaptation' : ARGV.shift
url = base_url + "/wiki/#{site}"
Signal.trap('INT') { exit }

# fetch the first link from the first paragraph of the site
CSS_SELECTOR = '#mw-content-text p a'
link_num = 0

# maximum links to skip
MAX_SKIPS = 10

# array of visited sites
sites = [site]

# skip pronounciation links
class PronunciationLink < StandardError; end
# skip links to files like images or audio
class FileLink < StandardError; end
class NoPhilosophy < StandardError; end

puts site
#require 'byebug'; byebug
loop do
  html = Nokogiri::HTML(URI.open(url))
  raise NoPhilosophy if link_num > MAX_SKIPS
  element = html.css(CSS_SELECTOR)[link_num]
  # raise exception of there is no link in the first paragraph
  raise NoPhilosophy if element.nil?
  site, site_href = [element.text, element['href']]

  raise PronunciationLink if site.match(%r(^[\[/].*[\]/]$)) || site_href.downcase.match(/help:pronun/)
  raise FileLink if site_href.match(/.*\.(ogg|png|jpg)/)

  sites << site
  puts sites.last
  url = base_url + site_href

  (puts "Reached philosophy!"; exit) if sites.last.downcase == 'philosophy'

  # exit if there is a repeated site
  raise NoPhilosophy if sites.uniq!

  link_num = 0

rescue NoMethodError, TypeError, PronunciationLink, FileLink, OpenURI::HTTPError
  link_num += 1
  puts "Skipped #{link_num} link#{link_num > 1 ? 's' : ''} in #{sites.last}"
rescue NoPhilosophy
  puts "Did not reached philosophy :("
  exit
end