Render a complete page in rails 3 without controller

call_template.rb

# create the template
template = PageOfflineTemplate.new
template.quote = quote
template.pages = quote.build_pages
        
# Here I render a template with layout to a string then a PDF
pdf = PDFKit.new template.render_to_string(:template=>"quotes/review.html.haml")
        

offline_template.rb

class OfflineTemplate < AbstractController::Base
  # Include all the concerns we need to make this work
  include AbstractController::Logger
  include AbstractController::Rendering
  include AbstractController::Layouts
  include AbstractController::Helpers
  include AbstractController::Translation
  include AbstractController::AssetPaths
  include ActionController::UrlFor
  include Rails.application.routes.url_helpers

  # this is you normal rails application helper
  helper ApplicationHelper

  # Define additional helpers, this one is for csrf_meta_tag
  helper_method :protect_against_forgery?

  # override the layout in your subclass if needed.
  layout 'application'
  
  # configure the different paths correctly
  def initialize(*args)
    super()
    lookup_context.view_paths = Rails.root.join('app', 'views')
    config.javascripts_dir = Rails.root.join('public', 'javascripts')
    config.stylesheets_dir = Rails.root.join('public', 'stylesheets')
    config.assets_dir = Rails.root.join('public')
  end
  
  # we are not in a browser, no need for this
  def protect_against_forgery?
    false
  end
  
  # so that your flash calls still work
  def flash
    {}
  end

  def params
    {}
  end
  
  # same asset host as the controllers
  self.asset_host = ActionController::Base.asset_host
  
  # and nil request to differentiate between live and offline
  def request
    nil
  end
end

page_offline_template.rb

# subclass to define the @ attributes your tempalte will use
class PageOfflineTemplate < OfflineTemplate
  attr_accessor :pages, :quote, :invoice, :quotes, :mat_pages, :wo_pages, :exp_pages
end

Blimey. I think Joe Armstrong nailed it when he said:

I think the lack of reusability comes in object-oriented languages, not functional languages. Because the problem with object-oriented languages is they’ve got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle.

If you have referentially transparent code, if you have pure functions — all the data comes in its input arguments and everything goes out and leave no state behind — it’s incredibly reusable.

Had to do this for Rails 5.0.6:

class OfflineTemplate < AbstractController::Base
  include AbstractController::Logger
  include AbstractController::Rendering
  include ActionView::Layouts
  include AbstractController::Helpers
  include AbstractController::Translation
  include AbstractController::AssetPaths
  include ActionDispatch::Routing::UrlFor
  include Rails.application.routes.url_helpers
  Rails.application.routes.default_url_options = Rails.application.config.action_mailer.default_url_options

  helper ApplicationHelper

  helper_method :protect_against_forgery?

  # configure the different paths correctly
  def initialize(*_args)
    super
    lookup_context.view_paths = Rails.root.join('app', 'views')
    config.javascripts_dir = Rails.root.join('public', 'javascripts')
    config.stylesheets_dir = Rails.root.join('public', 'stylesheets')
    config.assets_dir = Rails.root.join('public')
  end

  # we are not in a browser, no need for this
  def protect_against_forgery?
    false
  end

  # so that your flash calls still work
  def flash
    {}
  end

  def params
    {}
  end

  def controller_name
    'offline'
  end

  # same asset host as the controllers
  self.asset_host = ActionController::Base.asset_host
end