Silly-simple Amazon price watching script in Ruby

price_watcher.rb

require 'open-uri'
require 'hpricot'

MINUTES_BETWEEN_CHECKS = 15
URLS = ['http://www.amazon.com/Programming-Ruby-1-9-Pragmatic-Programmers/dp/1934356085/',
        'http://www.amazon.com/Ultimate-Hitchhikers-Guide-Galaxy/dp/0345453743/']
HISTORY_COUNT = 50
CURRENT_PRICE_ELEMENT = '.priceLarge'

prices = {}
start_time = Time.now

# http://stackoverflow.com/questions/4136248/how-to-generate-a-human-readable-time-range-using-ruby-on-rails
def humanize secs
  [[60, :seconds], [60, :minutes], [24, :hours], [1000, :days]].map{ |count, name|
    if secs > 0
      secs, n = secs.divmod(count)
      "#{n.to_i} #{name}"
    end
  }.compact.reverse.join(' ')
end

while true
  run_time_seconds = Time.now - start_time
  puts "-" * 80
  puts "\n"
  puts "Performing check at #{ Time.now.to_s }, running for #{humanize run_time_seconds}"
  
  URLS.each do |url|
    doc = open(url) { |f| Hpricot(f) }
    price_string = doc.search(CURRENT_PRICE_ELEMENT).inner_html
    
    puts "\nItem: #{doc.search('title').inner_html}\nCurrent Price: #{price_string}\n"
    
    if prices.has_key?(url)
      prices[url].unshift(Float(price_string.gsub('$', '')))
    else
      prices[url] = [Float(price_string.gsub('$', ''))]
    end
    
    if (prices.length > HISTORY_COUNT)
      prices[url].pop
    end
    
    puts "History: " + prices[url][0...HISTORY_COUNT].join(', ') + " ..."
    
  end
  puts "\nNext check in #{MINUTES_BETWEEN_CHECKS} minutes..."
  puts "\n"
  sleep(60 * MINUTES_BETWEEN_CHECKS)
end