Using nanoc to generate a cache-busting URL for external assets.

helper.rb

  # Given an item identifier, generate its fully-qualified URL along with the
  # item's hash as a query string parameter. Omit this cache-busting mechanism
  # in development environments so that HTML documents including this resource
  # aren't re-rendered with every change to the asset.
  def cache_bust_path( identifier )
    static = StorageHelper::static
    item = static[:assets][identifier]
    if !item
      return identifier
    end

    if static[:live]
      # Use the path to the minified representation (where available)
      if item.rep_named(:minified)
        path = item.path({ rep: :minified })
      else
        path = item.path()
      end
      # The `checksum` attribute specifies a checksum for both the the item's
      # contents and the item's attributes. These two checksums are
      # comma-separated. Remove the attribute checksum to avoid generating
      # overlong URLs.
      path += "?checksum=" + item.checksum.split(",")[0]
    else
      path = item.path()
    end

    path
  end