class Haml::Buffer

def self.merge_attrs(to, from)
  from['id'] = Compiler.filter_and_join(from['id'], '_') if from['id']
  if to['id'] && from['id']
    to['id'] << '_' << from.delete('id').to_s
  elsif to['id'] || from['id']
    from['id'] ||= to['id']
  end
  from['class'] = Compiler.filter_and_join(from['class'], ' ') if from['class']
  if to['class'] && from['class']
    # Make sure we don't duplicate class names
    from['class'] = (from['class'].to_s.split(' ') | to['class'].split(' ')).sort.join(' ')
  elsif to['class'] || from['class']
    from['class'] ||= to['class']
  end
  from_data = from['data'].is_a?(Hash)
  to_data = to['data'].is_a?(Hash)
  if from_data && to_data
    to['data'] = to['data'].merge(from['data'])
  elsif to_data
    to = Haml::Util.map_keys(to.delete('data')) {|name| "data-#{name}"}.merge(to)
  elsif from_data
    from = Haml::Util.map_keys(from.delete('data')) {|name| "data-#{name}"}.merge(from)
  end
  to.merge!(from)
end