```ruby
require 'cgi'
require 'rest_client'

module Graphite
  class Render
    def initialize(options={})
      @target = options[:target]
      @functions = []
    end

    def url(format=:png)
      options = url_options.merge("format" => format.to_s)
      "#{Configuration.instance.endpoint}/render?#{params(options)}"
    end

    def download(format=:png)
      RestClient.get url(format)
    end

    def add_function(*function)
      if function.size > 1
        @functions << [function.first.to_sym, function[1..-1]]
      else
        @functions << function.first.to_sym
      end
    end

    private

    def target
      target = @target
      @functions.each do |function|
        if function.is_a? Symbol
          target = %Q{#{function}(#{target})}
        else
          args = function.last.map{ |arg| %Q{"#{arg}"} }.join(",")
          target = %Q{#{function.first}(#{target},#{args})}
        end
      end

      target
    end

    def url_options
      {
        "target" => target
      }
    end

    def params(options={})
      options.map do |key,value|
        "#{CGI.escape(key)}=#{CGI.escape(value)}"
      end.join("&")
    end
  end
end
```

Add easier to understand return values
user
```ruby
require 'cgi'
require 'rest_client'

module Graphite
  class Render
    def initialize(options={})
      @target = options[:target]
      @functions = []
    end

    def url(format=:png)
      options = url_options.merge("format" => format.to_s)
      "#{Configuration.instance.endpoint}/render?#{params(options)}"
    end

    def download(format=:png)
      RestClient.get url(format)
    end

    def add_function(*function)
      if function.size > 1
        @functions << [function.first.to_sym, function[1..-1]]
      else
        @functions << function.first.to_sym
      end

      target
    end

    private

    def target
      target = @target
      @functions.each do |function|
        if function.is_a? Symbol
          target = %Q{#{function}(#{target})}
        else
          args = function.last.map{ |arg| %Q{"#{arg}"} }.join(",")
          target = %Q{#{function.first}(#{target},#{args})}
        end
      end

      target
    end

    def url_options
      {
        "target" => target
      }
    end

    def params(options={})
      options.map do |key,value|
        "#{CGI.escape(key)}=#{CGI.escape(value)}"
      end.join("&")
    end
  end
end
```
assistant