SASS Extension for dynamic absolute paths

extension.rb

# This extension makes the SASS function "application_resources_url" available, which will return the absolute path within a spring mvc managed application.
# 
# The implementation relays on a central java properties file located at src/main/resources/application.properties. It should contain at least following keys
#  webapp.version -- a string, e.g. 1.0.0
#  webapp.build   -- a string, e.g. 45
#  webapp.context -- a string, e.g. app (optional, if empty only / will be used)
#
#   Version 1.0 (2012-05-23, Jan Philipp <[email protected]>)
#   Under MIT License
#  

# Helper for application_resources_url()
class JavaProperties
  def self.load(path)
    File.open(path)
  end

  def self.get(path, key)
    result=nil
    File.open(path) { |file| opts=YAML.load(file); result = opts[key]}
    return result
  end
end

# Usage, e.g.: Write:  $pie-behavior: url(application_resources_url() + "/stylesheets/PIE.htc");
#              Result:                url("/app/resources-1.0.0.0/stylesheets/PIE.htc");
module Sass::Script::Functions
  def application_resources_url()
    context = JavaProperties.get 'src/main/resources/application.properties', 'webapp.context'
    version = JavaProperties.get 'src/main/resources/application.properties', 'webapp.version'
    build = JavaProperties.get 'src/main/resources/application.properties', 'webapp.build'
    path = "/"
    path += "#{context}/" if context
    path += "resources"
    path += "-#{version}.#{build}" if version
    
    Sass::Script::String.new(path)
  end
  declare :application_resources_url, :args => []
end