#Ice Template System

The Ice system for templating allows people to serve Javascript/Coffeescript templates from Rails applications. Its approach is similar to that taken by Liquid and some other template systems.

Using Javascript/Coffeescript has a few nice aspects

• It is easy to store these templates in your database. Therefore, your users can upload templates that are evaluated and served, but do not execute malicious code.
• By using Javascript/Coffeescript, you have the advantage of running your views on both the server and the browser (reducing code duplication).
• Also, thanks to Javascript/Coffeescript, your users have the ability to modify the templates in exciting ways, using their own code libraries.

Ice builds upon The Ruby Racer (written by Charles Lowell). This gem lets you use Google's V8 Javascript engine to execute your templates inside a sandbox.

Ice allows you to write your templates in one of two formats.

• Eco (written by Sam Stephenson). This gem allows you to use Coffeescript with HTML in an ERB-ish fashion.
• CoffeeKup (written by Maurice Machado). This library uses Coffeescript itself to define your templates in a way reminiscent of Markaby and Haml.

You can then write Eco templates like:

<table>
    <tr><th>Name</th><th>Email</th></tr>
    <% for user in @users %>
        <tr>
            <td><%= user.name %></td><td><%= mailTo(user.email) %></td>
        </tr>
    <% end %>
</table>

Eco-formatted files may also exist in your views directory, provided they have a .eco extension. An example of how this works is in this blog post.

Also, the templates may be compiled on demand with the method:

Ice::Handlers::Eco.convert_template(template_text, variables)

The CoffeeKup equivalent to the above Eco template is:

table ->
    tr ->
        th -> "Name"
        th -> "Email"
    for user in @users ->
        tr ->
            td -> user.name
            td ->  mailTo(user.email)

Similarly, these CoffeeKup files may exist on your filesystem provided they have a .coffeekup extension. A demo of this is in this screencast.

And you'd compile them on demand with:

Ice::Handlers::CoffeeKup.convert_template(template_text, variables)

Eventually I'd like to bring in other JS template libraries, but Eco and CoffeeKup should suffice for now. If you like Erb, use Eco. If you like Haml, use CoffeeKup.

Ice is currently being developed only for Rails 3. Simply add to your Gemfile

gem 'ice'

Ice is undergoing very active development so be sure to either use the most recent gem, or pull from master.

Every object is revealed to the templates via its to_ice method. This helps sanitize the objects that are passed into Ice, so people editing the template only have access to a limited subset of the data. This prevents people from adding code like:

<h1>Hi, <%= User.delete_all %></h1>

Instances of some classes like String and Numeric just return themselves as the result of to_ice. Hashes and Arrays run to_ice recursively on their members.

If you want an object to map to a different representation, simply define a to_ice object that returns whatever object you want to represent it within the Ice template. These objects are referred to as "Cubes", and are equivalent to "Drops" for those used to Liquid.

To make life easy, since most complex objects passed to the templates will be classes including ActiveModel::Serializable, the default to_ice behaviour of these classes is to pass itself in to a class with the same name, but followed by the word "Cube".

Therefore calling to_ice on an instance of a User class will invoke

UserCube.new self

You can have your cubes inherit from our Ice::BaseCube class. Your cubes inheriting from it can then determine what additional attributes they want to reveal. For example

class BookCube < Ice::BaseCube
  revealing :title, :author_id, :genre_id

  def reviewer_names
    @source.reviewers.map(&:name)
  end
end

would provide a cube with access to the title, author_id and genre properties of the underlying ActiveModel. In addition, it exposes a reviewer_names function that uses the @source instance variable to get at the record which is being filtered. Note that if no call to revealing occurs, the cube generates a mapping for the @source object's serializable attributes.

These cubes also have simple belongs_to and has_many associations, so you can write things like:

class ArticleCube < Ice::BaseCube
  has_many :comments, :tags
  belongs_to :author, :section
end

This generates association helper functions such as comment_ids, num_comments, has_comments, comments, author_id, and author.

Note that the results of all associations and revealed functions are also sanitized via to_ice.

Partials may now be written in Eco or CoffeeKup, and included in ERB (and other) templates.

Two global arrays exist named IceJavascriptHelpers and IceCoffeescriptHelpers. If you add to those arrays strings of Javascript or Coffeescript, those strings will be included in your views. These string are also compiled in the case of Coffeescript.

This is slightly hackish, so expect this approach to shortly be replaced with a better one. But it is a quick way to add helpers to Ice.

To make it easier to generate links, we added a navBar helper. For Eco templates it appears as:

<%= navBar (bar) => %>
    <%= bar.linkTo("Bar", "/foo") %>
    <%= bar.linkTo("http://ludicast.com") %>
<% end %>

and in CoffeeKup the navBar is written as:

navBar (o)=>
    o.linkTo("Bar", "/foo")
    o.linkTo("http://ludicast.com")

In either case this generates the following html

<ul class="linkBar">
    <li><a href="/foo">Bar</a></li>
    <li><a href="http://ludicast.com">http://ludicast.com</a></li>
</ul>

The navBar helper also takes options so if the Eco above was instead instantiated with:

<% opts = nav_prefix:'<div>', nav_postfix: '</div>', link_prefix: '<span>', link_postfix: '</span>' %>
<%= navBar opts, (bar)=> %>

it would generate

<div>
    <span><a href="/foo">Bar</a></span>
    <span><a href="http://ludicast.com">http://ludicast.com</a></span>
</div>

Also, if you want to make a site-wide change to the default NavBar settings, all you need to do is add these options to the NavBarConfig class like

coffeescript = <<-COFFEESCRIPT
  NavBarConfig =
    navPrefix: "<div>",
    navPostFix: "</div>",
    linkPrefix: "<span>",
    linkPostFix: "</span>"
COFFEESCRIPT
IceCoffeescriptHelpers << coffeescript

Then all links will generate with these options, unless overridden in the values passed in to navBar.

Assuming that all your cubes are models that you are exposing to your app, we add to Ice routing helpers for every class inheriting from BaseCube. Therefore, if you have a cube class named NoteCube, you will have the following helper methods available:

newNotePath
notesPath
notePath(@note)
editNotePath(@note)

which are converted to the appropriate paths.

Note that some people might claim that it is insecure to expose your resources like this, but that probably should be dealt with on a case-by-case basis. Besides, the fact that you are exposing these resources as cubes means that you are, well, already exposing these resources.

• Fork the project.
• Make your feature addition or bug fix.
• Add spec for it. This is important so I don't break it in a future version unintentionally. In fact, try to write your specs in a test-first manner.
• Commit
• Send me a pull request.

• Add in form builders (from clots project)
• Use Moneta for caching autogenerated javascript files.
• Allowing Ice to render partials
• Allowing Ice to serve as Rails layout files.

MIT Licence. See MIT-LICENSE file for details.