Rails Metal theme switcher

application.html.erb

# your applications main layout file (app/views/layouts/application.html.erb?)  
# I put this after the normal stylesheet call, so our theme can override what we want instead of the entire stylesheet  
  
<% if theme = request.env['rails.theme'] %>  
  <%= stylesheet_link_tag "themes/#{theme}", :media => :all %>  
<% end %>  

name_of_theme.css

/* 
RAILS_ROOT/public/stylesheets/themes/st_patricks_day.css 
{{ 
    theme=st patricks day 
    &begin=March 17 
    &end=March 18 
    &enabled=1 
}} 
*/  
  
#header{  
    background:#C2DDCA url(theme_images/shamrock.png) no-repeat 25px 20px;  
    padding-left:50px;  
    }  

theme.rb

# app/metal/theme.rb

class Theme
  # this is where the theme index is stored
  CacheKey = 'themes'
  # this is what we will look for in the layout
  ThemeEnvKey = 'rails.theme'
  # this is the path to your themes folder
  ThemesPath = File.join(RAILS_ROOT, 'public', 'stylesheets', 'themes')

  def self.call(env)
    # Build our theme index
    themes = Rails.cache.fetch(CacheKey) do
      data = {}
      Dir[File.join(ThemesPath, '*.css')].each do |theme|
        # looks for {{ url_type_string_here }} comment meta data and parses
        # it out into a hash for the theme's file name
        #
        # within your theme file, you would have:
        #   {{theme=my name&begin=DATE&end=DATE}}
        # becomes
        #   {'theme.css' => {:theme => 'my mane', :begin => 'START_DATE', :end => 'FINISH_DATE'}}
        #
        # DATE is parsed so it can be any type of
        # date-ish string see ActiveSupport::TimeZone#parse
        begin
          data[File.basename(theme)] = \
            $1.split('&').inject({}) do |h, v|
              s = v.split('=').map(&:strip)
              h[s.first.to_sym] = s.last
              h
            end if File.read(theme) =~ /\{\{(.+)\}\}/m
        rescue Exception => e
          data[theme] = {:error => e.to_s}
        end
      end
      data
    end

    # Set the appropriate theme
    now = Time.zone.now.beginning_of_day
    themes.each_pair do |file, data|
      next if data.keys.include?(:enabled) and data[:enabled].to_i.zero?
      next unless data.keys.include?(:begin) and data.keys.include?(:end)

      if Time.zone.parse(data[:begin]) <= now and Time.zone.parse(data[:end]) > now
        env[ThemeEnvKey] = file
        break
      end
    end

    # pass
    Rails::Rack::Metal::NotFoundResponse
  end
end