tag_cloud by mime type? #9

I've noticed that if I scope a tag cloud to a mime type, the tag cloud is styled based on the occurrence of tags across all assets, not just the assets of the scoped mime type.

For example, I'm working on a site that features photos that are tagged by artists, and magazines that are tagged by artists and topics. I want the magazine tag cloud to reflect the occurrence of artists' tags across magazines, rather than across magazines and photos.

This is the band-aid solution I've come up with, you could certainly make this slicker:

# in taggable_tags.rb
# I've added support for a 'for' attribute for specifying mime type
# ex. r:pdf_tags:cloud for="pdf" /
tag 'tags:cloud' do |tag|
    if tag.locals.tags && tag.locals.tags.length > 1
    options = tag.attr.dup
    media_type = options.delete('for')
    tag.locals.tags = Tag.for_cloud(tag.locals.tags, media_type).sort_by{|t| t.title.downcase}

# in tag.rb

  named_scope :only_assets_of_type, lambda { |tags|
    {
      :conditions => ["tt.tagged_id IN (#{tags.map{'?'}.join(',')})", *tags.map{|t| t.is_a?(Tag) ? t.id : t}]
    }
  }

def  self.for_cloud(tags, type=nil)
    return tags if tags.empty? || tags.first.cloud_size
    if type
     sized(in_this_list(tags).with_count.only_assets_of_type(Asset.not_furniture.send(type.pluralize.intern)))
    else
      sized(in_this_list(tags).with_count)
    end
end

I'm not sure if this kind of functionality is something you think belongs in the extension, or maybe this is an edge case.