Linking to an image and extracting dimensions

image_link.rb

def image_link(identifier, rep_name)
  item = @items[identifier]
  rep = item.rep_named(rep_name)

  # Create soft dependency
  # (i.e. when the image changes, this page will be recompiled)
  Nanoc::NotificationCenter.post(:visit_started, item)
  Nanoc::NotificationCenter.post(:visit_ended,   item)

  # Create hard dependency
  # (i.e. this page requires the item to be compiled already)
  if !rep.compiled?
    raise Nanoc::Errors::UnmetDependency.new(rep)
  end

  # TODO: implement #extract_dimensions
  width, height = extract_dimensions(rep.raw_path)

  %[<img src="#{rep.path}" width="#{width}" height="#{height}">]
end