gistfile1.rb

#!/usr/bin/env ruby
require 'net/http'
require 'json'

def http_get(url)
  puts "http_get: #{url}"
  return Net::HTTP.get(URI(url))
end
  
def handle_http(response, url)
  if response['You should try JSON']
    return url.sub 'challenge?id', 'challenge.json?id'
  elsif response =~ /^{"follow":"http:\/\/[\w\.\/]+\?id=\d+"}$/
    return JSON.parse(response).fetch('follow').sub 'challenge?id', 'challenge.json?id'
  else
    puts response
  end
  return nil
end

def play_with(url)
  begin
    response = http_get(url)
    url = handle_http(response, url)
  end while not url.nil?
end

play_with(ARGV.shift)