sinbook: simple sinatra facebook extension in 300 lines of ruby
  (c) 2009 Aman Gupta (tmm1)

=== Usage

  require 'sinbook'
  require 'sinatra'

  facebook do
    api_key  '4579...cbb0'
    secret   '5106...2342'
    app_id   81747826609
    url      'http://apps.facebook.com/myappname'
    callback 'http://myappserver.com'
  end

  get '/' do
    fb.require_login!
    "Hi <fb:name uid=#{fb[:user]} useyou=false />!"
  end


=== Features

  sinbook provides a simple `facebook` helper (also aliased to `fb`).

    >> fb.valid?
    => true                              # valid (authenticated) request from facebook's servers

    >> pp fb.params
    {
      :logged_out_facebook => false,     # request came from a user logged into facebook
      :added => true,                    # user is logged into our app
      :user => 1234,                     # user's facebook uid
      :friends => [1,2,3],               # list of user's friends
      ...
    }

    >> fb[:user]                         # [] is aliased to params[]
    => 1234

    >> fb.callback
    => 'http://apps.facebook.com/myappname'

    >> fb.callback('/homepage')
    => 'http://apps.facebook.com/myappname/homepage'

    >> fb.url('/images/static.gif')
    => 'http://myappserver.com/images/static.gif'

    >> fb.appurl
    => 'http://apps.facebook.com/add.php?api_key=4579...cbb0'

    >> fb.addurl
    => 'http://www.facebook.com/apps/application.php?id=81747826609'

    >> fb.redirect('/welcome')           # redirect using an fb:redirect tag

    >> fb.require_login!                 # redirect to addurl page unless logged in


  The helper can also be used to make API calls

    >> fb.users.getInfo :uid => 1234, :fields => [:name]
    => [{'uid' => 1234, 'name' => 'Frank Sinatra'}]

    >> fb.groups.get :uid => 1234
    => [{'name' => 'Sinatra Users'}]

    >> fb.profile.setFBML :profile => 'hello world'
    => true

    >> fb.profile.getFBML
    => 'hello world'


=== TODO

  * Switch to yajl-ruby for json parsing
  * Split out facebook api client so it can be used outside sinatra
  * Add a batch mode for api calls:

      groups, pics = fb.batch do |b|
        b.groups.get :uid => 123
        b.users.getInfo :uids => 123, :fields => [:pic_square]
      end