AR to store previews.

embedly-preview-store.rb

  class Preview < Base

    def self._key url
      Digest::SHA1.hexdigest(url)
    end

    def self.key_exists? url
      find_redirect(url) or find_preview(url)
    end

    def self.find_redirect url
      key = "r::#{_key url}"
      find(:first, :conditions => {:key => key})
    end

    def self.find_preview url
      key = "p::#{_key url}"
      prev = find(:first, :conditions => {:key => key})
      return prev if prev
      if redirect = find_redirect(url)
        return find_preview(redirect.value)
      else
        nil
      end
    end

    def self.save_preview requested_url, preview
      if preview.url != requested_url
        key = "r::#{_key requested_url}"
        # does the redirect exist?
        r = find(:first, :conditions => { :key => key })
        # it does, so update if needed
        if r and r.value != preview.url
          r.value = preview.url
          r.save
        # nope, let's created it
        else
          create :key => key, :value => preview.url
        end
      end

      key = "p::#{_key preview.url}"
      create :key => key, :value => 
          preview.marshal_dump.to_json
    end
  end