Nested LoadableComponents in Ruby

tryselenium.rb

require 'selenium-webdriver'

#
# Read more about LoadableComponent here: 
# 
#   http://code.google.com/p/selenium/wiki/LoadableComponent
# 

class LoadableComponent
  attr_reader :driver
  
  class UnableToLoadComponent < StandardError; end
  
  def initialize(driver, parent = nil)
    @driver = driver
    @parent  = parent
  end
  
  def load
    raise "subclass' responsibility"
  end
  
  def loaded?
    raise "subclass' responsibility"
  end
  
  def get
    load unless loaded?

    unless loaded?
      raise UnableToLoadComponent, unable_to_load_message
    end
    
    self
  end
  
  private
  
  def unable_to_load_message
    "could not load #{self.class.name}" 
  end
  
  # shouldn't really live here
  def self.wait(timeout, name = :wait)
    define_method name do
      @wait ||= Selenium::WebDriver::Wait.new(:timeout => timeout)
    end
  end
end

class Tweeter
  def initialize(user, pass)
    @user = user
    @pass = pass
  end
  
  def tweet(str)
    main_page.get.tweet str
  end
  
  private
  
  def driver
    @driver ||= Selenium::WebDriver.for :firefox
  end
  
  def login_page
    @login_page ||= LoginPage.new(driver, @user, @pass)
  end
  
  def main_page
    @main_page ||= MainPage.new(driver, login_page)
  end
  
  class LoginPage < LoadableComponent
    wait 5
    
    def initialize(driver, user, pass)
      super(driver)
      @user, @pass = user, pass
    end
    
    def login
      user_field.send_keys @user
      password_field.send_keys @pass
      
      sign_in_button.click
    end
    
    def load
      driver.get "http://twitter.com/login"
      
      wait.until { user_field.displayed? }
    end
    
    def loaded?
      user_field
      true
    rescue Selenium::WebDriver::Error::NoSuchElementError
      false
    end
    
    private
    
    def user_field
      driver[:name => 'session[username_or_email]']
    end
    
    def password_field
      driver[:name => 'session[password]']
    end
    
    def sign_in_button
      driver[:class => "signin"].first(:xpath => "//button[@type='submit']")
    end
  end # LoginPage
  
  class MainPage < LoadableComponent
    wait 5
    
    def tweet(str)
      tweet_box.send_keys str
      wait.until { tweet_button.enabled? }
      
      last = last_tweet_id
      
      begin
        tweet_button.click
      rescue Selenium::WebDriver::Error::ElementNotDisplayedError
        raise "firefox needs focus to post a tweet"
      end
      
      wait.until { last_tweet_id != last }
    end
    
    def load
      @parent.get.login
      driver.switch_to.default_content # Fx4 bug
    end
    
    def loaded?
      driver['session']['class'] == "loggedin"
    rescue Selenium::WebDriver::Error::NoSuchElementError
      false
    end
    
    def unable_to_load_message
      "could not log in - captcha?"
    end
    
    private
    
    def last_tweet_id
      driver[:class => "stream-item"]['data-item-id']
    end
    
    def tweet_box
      driver[:class => "twitter-anywhere-tweet-box-editor"]
    end
    
    def tweet_button
      driver[:class => "tweet-button"]
    end
  end # MainPage
end # Tweeter

if __FILE__ == $0
  abort "USAGE: #{$PROGRAM_NAME} user pass" unless ARGV.size == 2
  Tweeter.new(*ARGV).tweet("#SeConf is awesome! http://tryselenium.org")
end