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require 'nokogiri'
require 'fastimage'
module Jekyll
module AmpFilter
# Filter for HTML 'img' elements.
# Converts elements to 'amp-img' and adds additional attributes
# Parameters:
# input - the content of the post
# responsive - boolean, whether to add layout=responsive, true by default
def amp_images(input, responsive = true, wi = nil, he = nil)
doc = Nokogiri::HTML.fragment(input);
# Add width and height to img elements lacking them
doc.css('img:not([width])').each do |image|
if wi && he
image['width'] = wi
image['height'] = he
else
if image['src'].start_with?('http://', 'https://')
src = image['src']
else
# FastImage doesn't seem to handle local paths when used with Jekyll
# so let's just force the path
src = File.join(Dir.pwd, '_site', image['src'])
end
# Jekyll generates static assets after the build process.
# This causes problems when trying to determine the dimensions of a locally stored image.
# For now, the only solution is to skip the build and generate the AMP files after the site has beem successfully built.
# TODO: find a better solution.
begin
size = FastImage.size(src)
image['width'] = size[0]
image['height'] = size[1]
rescue Exception => e
puts 'Unable to get image dimensions for "' + src + '". For local files, build the site with \'--skip-initial-build\' for better results. [Error: ' + e.to_s + ']'
end
end
end
# Change 'img' elements to 'amp-img', add responsive attribute when needed
doc.css('img').each do |image|
image.name = "amp-img"
image['layout'] = "responsive" if responsive
end
# Picture elements are not accepted in amp pages, convert them to amp-img
#<picture>
# <source srcset="mdn-logo-wide.webp" type="image/webp">
# <source srcset="mdn-logo-wide.png" media="(min-width: 600px)">
# <img src="mdn-logo-narrow.png" alt="MDN">
#</picture>
# Move amp-img elements inside picture elements outside of it and remove picture elements
doc.css('picture').each do |picture|
# Get img element from picture
amp_img = picture.css('amp-img')
picture.add_next_sibling(amp_img) unless amp_img.empty?
# Remove picture element
picture.remove
end
# Added <img /> tag wrapped with <noscript /> in case js is not enabled
# but image will still show up. The element would look like this:
# <amp-img ...>
# <noscript>
# <img ... />
# </noscript>
# </ampimg ...>
# Duplicate amp-img, remove layout attribut, wrap it with noscript, and add
# it as amp-img child
doc.css('amp-img').each do |amp_img|
noscript = Nokogiri::XML::Node.new "noscript", doc
noscript_img = amp_img.dup
noscript_img.remove_attribute('layout')
noscript_img.name = 'img'
noscript.add_child(noscript_img)
amp_img.add_child(noscript)
end
# Return the html as plaintext string
doc.to_s
end
end
end
Liquid::Template.register_filter(Jekyll::AmpFilter)