class Middleman::Sources

def watch(type_or_handler, options={})
  handler = if type_or_handler.is_a? Symbol
    path = File.expand_path(options.delete(:path), app.root)
    SourceWatcher.new(self, type_or_handler, path, options)
  else
    type_or_handler
  end
  @watchers << handler
  # The index trick is used so that the sort is stable - watchers with the same priority
  # will always be ordered in the same order as they were registered.
  n = 0
  @sorted_watchers = @watchers.sort_by do |w|
    priority = w.options.fetch(:priority, 50)
    n += 1
    [priority, n]
  end.reverse.freeze
  handler.on_change(&method(:did_change))
  if @running
    handler.poll_once!
    handler.listen!
  end
  handler
end