post.rb

class Post < ActiveRecord::Base
  attr_accessible :title, :body

  acts_as_commentable

  # validations
  belongs_to :author, :class_name => 'User', :foreign_key => 'user_id'
  validates_presence_of :body

  scope :with_title, :conditions => [ "title IS NOT NULL" ]
  scope :recent, lambda { |limit| {:limit => limit || 30, :order => 'created_at DESC'}}

  # callbacks
  fires :new_post, :on => :create, :actor => :author

  before_save :store_rendered_copy
  def store_rendered_copy
    if self.body_changed?
      self.rendered_body = render!
    end
    true
  end

  def to_s
    title || "este recado"
  end

  def body
    self.rendered_body ||= render!
  end

  private
  def render!
    raw = read_attribute(:body)
    if raw.present?
      embedded = Post.transform(raw)
      markdown = RDiscount.new(embedded) 
      rendered_body = markdown.to_html
    end
  end

  def self.transform(txt, *attrs, &block)
    ret = txt.dup
    extract_links!(txt) do |u|      
      transform_url_for_text!(u, ret, *attrs, &block)
    end
    ret
  end

  def self.transform_url_for_text!(u, txt, *attrs, &block)
    begin
      oembed = OhEmbedr::OhEmbedr.new(:url => u, *attrs)
      response = oembed.gets['html']
      txt.gsub!(u, response) if response.present?
    rescue OhEmbedr::Error => error
      # don't touch the string      
    end
  end

  def self.extract_links!(s, &block)
    reg = /(https?:\/\/[^\s]+)/i
    if block_given?
      s.scan(reg) { yield $& }
      nil
    else
      result = []
      str.scan(reg) { result.push $& }
      result
    end
  end
end