-- Add intrinsic dimensions to images that do not already specify them.
-- This reserves their layout space before the browser has loaded the file.
function Image(image)
  if image.attributes.width or image.attributes.height then
    return image
  end

  local ok, mime_type, contents = pcall(pandoc.mediabag.fetch, image.src)
  if not ok or not contents then
    return image
  end

  local sized, dimensions = pcall(pandoc.image.size, contents)
  if not sized then
    return image
  end

  image.attributes.width = tostring(math.floor(dimensions.width + 0.5))
  image.attributes.height = tostring(math.floor(dimensions.height + 0.5))
  return image
end