From: Kirk Haines <khaines@...>
Date: 2005-10-06T05:21:19+09:00
Subject: Re: CSS switcher in Ruby?

On Tuesday 04 October 2005 10:17 pm, Tom Cloyd wrote:
> I have no idea if this is a goofy idea or not (and I'm only just starting
> with Ruby and unable to attempt this project myself), but might a CSS
> switcher for web pages be possible in Ruby? Seems quite possible to me,
> but...

Possible, and generally easy, though the details depend a great deal on what 
environment one is running one's web stuff in.

I have two approaches.

One approach is for occasions where there may be both static and non-static 
pages that all need to have some intelligent stylesheet selection.  Often I 
use this just to have a special stylesheet for browsers that say they are IE, 
so that I don't have to deal with gross box model hacks and other pain 
involved in making a single stylesheet work with, say, IE and Firefox.

A version of the code I use for this style would look something like this:

class Styles < Iowa::Component
  @@styles_mtimes = {'styles.css' => 0, 'styles_nonie.css' => 0}
  @@styles = {}

  def styles
    session.context.request.content_type = 'text/css'
    begin
      headers = session.context.request.headers_in['User-Agent']
      # A very naive browser type check follows.
      style_file = header =~ /MSIE/ ? 'styles.css' : 'styles_nonie.css'
      if File.stat(style_file).mtime.to_i > @@styles_mtimes[style_file]
        @@styles[style_file] = File.read(style_file)
        @@styles_mtimes[style_file] = File.stat(style_file).mtime.to_i
      end
    rescue Exception
      # Something bad happened.  Do something?
    end
    @@styles[style_file]
  end
end


A variation of this could easily be used to select a stylesheet based on a 
cookie value, for more sophisticated CSS file switching.

The other approach that I use occasionally is to embed the logic at the other 
end, in the code that generates the original HTML page.

<link rel="stylesheet" type="text/css" href="@css_url" />

css_url would be a method that would return the URL to the desired CSS file. 
One obvious problem with this method is that it requires that the HTML page 
be dynamically generated.  Having a smart /styles.css delivery, on the other 
hand, means that even static HTML files can be served different stylesheets 
based on browser type or a cookie or some other trait, and that's how I 
usually approach this issue.  The browser never knows that the response from 
a request for /styles.css is being dynamically generated.


Kirk Haines