flexible url sanitizer

url_sanitizer.rb

module UrlSanitizer
  extend ActiveSupport::Concern

  require 'uri'

  # this concern creates a 'virtual' method, for example 'site_url=(arg)',
  # which validates and sanitizes url by metaprogramming magic

  # usage in model:
  # include UrlSanitizer
  # validates :site_url, :url => {:allow_nil => true} # gem 'validate_url'
  # after_initialize do
  #   sanitize_url :site_url
  # end

  def create_method(name, &block)
    self.class.send(:define_method, name, &block)
  end

  def sanitize_url(attribute_name)

    method_name = (attribute_name.to_s + '=')

    create_method(method_name) { |arg|
      sanitized_value = arg
      if sanitized_value.to_s.length > 0
        if sanitized_value.scan(URI.regexp).count < 1
          sanitized_value = 'http://' + sanitized_value
        end
      end
      write_attribute(attribute_name.to_sym, sanitized_value)
    }

  end

end