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7bdf47b864
Not all HTML elements are converted into Markdown. Some are kept as HTML. Without this fix XML/HTML entities that are formatted as text instead of code are swallowed by Discourse. This also fixes quotes in the `title` attribute of the `<abbr>` tag.
419 lines
10 KiB
Ruby
419 lines
10 KiB
Ruby
# frozen_string_literal: true
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require "securerandom"
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class HtmlToMarkdown
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def initialize(html, opts = {})
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@opts = opts
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@within_html_block = false
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# we're only interested in <body>
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@doc = Nokogiri.HTML5(html).at("body")
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remove_not_allowed!(@doc)
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remove_hidden!(@doc)
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hoist_line_breaks!(@doc)
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remove_whitespaces!(@doc)
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end
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def to_markdown
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traverse(@doc).gsub(/\n{2,}/, "\n\n").strip
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end
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private
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def strip_newlines(string)
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string.gsub(/\n/, " ")&.squeeze(" ")
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end
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def remove_not_allowed!(doc)
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allowed = Set.new(@opts[:additional_allowed_tags] || [])
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HtmlToMarkdown.private_instance_methods.each do |m|
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if tag = m.to_s[/^visit_(.+)/, 1]
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allowed << tag
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end
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end
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@doc.traverse { |node| node.remove if !allowed.include?(node.name) }
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end
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def remove_hidden!(doc)
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@doc.css("[hidden]").remove
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@doc.css("img[width]").each { |n| n.remove if n["width"].to_i <= 0 }
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@doc.css("img[height]").each { |n| n.remove if n["height"].to_i <= 0 }
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end
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# When there's a <br> inside an inline element, split the inline element around the <br>
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def hoist_line_breaks!(doc)
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klass = "_" + SecureRandom.hex
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doc.css("br").each { |br| br.add_class(klass) }
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loop do
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changed = false
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doc
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.css("br.#{klass}")
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.each do |br|
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parent = br.parent
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if block?(parent)
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br.remove_class(klass)
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else
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before, after = parent.children.slice_when { |n| n == br }.to_a
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if before.size > 1
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b = doc.document.create_element(parent.name)
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before[0...-1].each { |c| b.add_child(c) }
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parent.previous = b if b.inner_html.present?
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end
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if after.present?
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a = doc.document.create_element(parent.name)
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after.each { |c| a.add_child(c) }
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parent.next = a if a.inner_html.present?
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end
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parent.replace(br)
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changed = true
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end
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end
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break if !changed
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end
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end
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# Removes most of the unnecessary white spaces for better markdown conversion
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# Loosely based on the CSS' White Space Processing Rules (https://www.w3.org/TR/css-text-3/#white-space-rules)
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def remove_whitespaces!(node)
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return true if "pre" == node.name
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node
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.children
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.chunk { |n| is_inline?(n) }
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.each do |inline, nodes|
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if inline
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collapse_spaces!(nodes) && remove_trailing_space!(nodes)
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else
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nodes.each { |n| remove_whitespaces!(n) }
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end
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end
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end
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def is_inline?(node)
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node.text? ||
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("br" != node.name && node.description&.inline? && node.children.all? { |n| is_inline?(n) })
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end
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def collapse_spaces!(nodes, was_space = true)
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nodes.each do |node|
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if node.text?
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text = String.new
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node.text.chars.each do |c|
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if c[/[[:space:]]/]
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text << " " if !was_space
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was_space = true
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else
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text << c
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was_space = false
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end
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end
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node.content = text
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else
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node.children.each { |n| was_space = collapse_spaces!([n], was_space) }
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end
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end
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was_space
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end
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def remove_trailing_space!(nodes)
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last = nodes[-1]
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if last.text?
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last.content = last.content[0...-1] if last.content[-1] == " "
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elsif last.children.present?
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remove_trailing_space!(last.children)
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end
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end
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def traverse(node, within_html_block: false)
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within_html_block_changed = false
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if within_html_block
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within_html_block_changed = true
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@within_html_block = true
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end
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text = node.children.map { |n| visit(n) }.join
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@within_html_block = false if within_html_block_changed
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text
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end
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def visit(node)
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visitor = "visit_#{node.name}"
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send(visitor, node) if respond_to?(visitor, true)
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end
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ALLOWED_IMG_SRCS ||= %w[http:// https:// www.]
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def allowed_hrefs
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@allowed_hrefs ||=
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begin
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hrefs = SiteSetting.allowed_href_schemes.split("|").map { |scheme| "#{scheme}:" }.to_set
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ALLOWED_IMG_SRCS.each { |src| hrefs << src }
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hrefs << "mailto:"
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hrefs.to_a
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end
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end
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def visit_a(node)
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if node["href"].present? && node["href"].start_with?(*allowed_hrefs)
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"[#{traverse(node)}](#{node["href"]})"
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else
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traverse(node)
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end
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end
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def visit_img(node)
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return if node["src"].blank?
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node["alt"] = strip_newlines(node["alt"]) if node["alt"].present?
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node["title"] = strip_newlines(node["title"]) if node["title"].present?
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if @opts[:keep_img_tags]
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node.to_html
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elsif @opts[:keep_cid_imgs] && node["src"].start_with?("cid:")
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node.to_html
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elsif node["src"].start_with?(*ALLOWED_IMG_SRCS)
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width = node["width"].to_i
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height = node["height"].to_i
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dimensions = "|#{width}x#{height}" if width > 0 && height > 0
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"![#{node["alt"] || node["title"]}#{dimensions}](#{node["src"]})"
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end
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end
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ALLOWED ||= %w[kbd del ins small big sub sup dl dd dt mark]
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ALLOWED.each do |tag|
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define_method("visit_#{tag}") do |node|
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"<#{tag}>#{traverse(node, within_html_block: true)}</#{tag}>"
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end
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end
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def visit_blockquote(node)
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text = traverse(node)
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text.strip!
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text.gsub!(/\n{2,}/, "\n\n")
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text.gsub!(/^/, "> ")
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"\n\n#{text}\n\n"
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end
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BLOCKS ||= %w[div tr]
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BLOCKS.each do |tag|
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define_method("visit_#{tag}") do |node|
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prefix = block?(node.previous_element) ? "" : "\n"
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"#{prefix}#{traverse(node)}\n"
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end
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end
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def visit_p(node)
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"\n\n#{traverse(node)}\n\n"
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end
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TRAVERSABLES ||= %w[aside font span thead tbody tfoot u center]
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TRAVERSABLES.each { |tag| define_method("visit_#{tag}") { |node| traverse(node) } }
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def visit_tt(node)
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"`#{traverse(node)}`"
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end
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def visit_code(node)
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node.ancestors("pre").present? ? traverse(node) : visit_tt(node)
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end
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def visit_pre(node)
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text = traverse(node)
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fence = text["`"] ? "~~~" : "```"
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code = node.at("code")
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code_class = code ? code["class"] : ""
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lang = code_class ? code_class[/lang-(\w+)/, 1] : ""
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"\n\n#{fence}#{lang}\n#{traverse(node)}\n#{fence}\n\n"
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end
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def visit_br(node)
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"\n"
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end
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def visit_hr(node)
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"\n\n---\n\n"
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end
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def visit_abbr(node)
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title = node["title"].presence
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attributes = { title: } if title
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create_element("abbr", traverse(node, within_html_block: true), attributes).to_html
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end
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def visit_acronym(node)
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visit_abbr(node)
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end
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(1..6).each { |n| define_method("visit_h#{n}") { |node| "#{"#" * n} #{traverse(node)}" } }
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def visit_table(node)
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if (rows = extract_rows(node))
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headers = rows[0].css("td, th")
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text = "| " + headers.map { |td| traverse(td).gsub(/\n/, "<br>") }.join(" | ") + " |\n"
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text << "| " + (["-"] * headers.size).join(" | ") + " |\n"
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rows[1..-1].each do |row|
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text << "| " + row.css("td").map { |td| traverse(td).gsub(/\n/, "<br>") }.join(" | ") +
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" |\n"
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end
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"\n\n#{text}\n\n"
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else
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"<table>\n#{traverse(node, within_html_block: true)}</table>"
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end
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end
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def extract_rows(table)
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return if table.ancestors("table").present?
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return if (rows = table.css("tr")).empty?
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headers_count = rows[0].css("td, th").size
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return if rows[1..-1].any? { |row| row.css("td").size != headers_count }
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rows
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end
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def visit_tr(node)
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text = traverse(node)
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@within_html_block ? "<tr>\n#{text}</tr>\n" : text
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end
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TABLE_CELLS ||= %w[th td]
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TABLE_CELLS.each do |tag|
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define_method("visit_#{tag}") do |node|
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text = traverse(node)
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if @within_html_block
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element = create_element(tag, "\n\n#{text}\n\n")
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node.attribute_nodes.each do |a|
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element[a.name] = a.value if %w[rowspan colspan].include?(a.name)
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end
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"#{element.to_html}\n"
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else
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text
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end
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end
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end
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LISTS ||= %w[ul ol]
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LISTS.each do |tag|
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define_method("visit_#{tag}") do |node|
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prefix = block?(node.previous_element) ? "" : "\n"
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suffix = node.ancestors("ul, ol, li").size > 0 ? "" : "\n"
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"#{prefix}#{traverse(node)}#{suffix}"
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end
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end
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def visit_li(node)
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text = traverse(node)
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lists = node.ancestors("ul, ol")
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marker = "ol" == lists[0]&.name ? "1. " : "- "
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indent = (" " * marker.size) * [1, lists.size].max
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suffix = node == node.parent.elements[-1] ? "" : "\n"
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text.gsub!(/\n{2,}/, "\n\n")
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text.gsub!(/^(?!\s*$)/, indent)
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text.lstrip!
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"#{marker}#{text}#{suffix}"
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end
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EMPHASES ||= %w[i em]
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EMPHASES.each do |tag|
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define_method("visit_#{tag}") do |node|
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text = traverse(node)
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return "" if text.empty?
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return " " if text.blank?
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return "<#{tag}>#{text}</#{tag}>" if text["\n"] || (text["*"] && text["_"])
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prefix = text[0][" "]
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suffix = text[-1][" "] if text.size > 1
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wrap = text["*"] ? "_" : "*"
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"#{prefix}#{wrap}#{text.strip}#{wrap}#{suffix}"
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end
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end
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STRONGS ||= %w[b strong]
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STRONGS.each do |tag|
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define_method("visit_#{tag}") do |node|
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text = traverse(node)
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return "" if text.empty?
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return " " if text.blank?
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return "<#{tag}>#{text}</#{tag}>" if text["\n"] || (text["*"] && text["_"])
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prefix = text[0][" "]
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suffix = text[-1][" "] if text.size > 1
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wrap = text["*"] ? "__" : "**"
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"#{prefix}#{wrap}#{text.strip}#{wrap}#{suffix}"
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end
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end
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STRIKES ||= %w[s strike]
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STRIKES.each do |tag|
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define_method("visit_#{tag}") do |node|
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text = traverse(node)
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return "" if text.empty?
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return " " if text.blank?
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return "<#{tag}>#{text}</#{tag}>" if text["\n"] || text["~~"]
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prefix = text[0][" "]
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suffix = text[-1][" "] if text.size > 1
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"#{prefix}~~#{text.strip}~~#{suffix}"
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end
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end
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def visit_text(node)
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if @within_html_block
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node.to_html
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else
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node.text
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end
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end
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HTML5_BLOCK_ELEMENTS ||= %w[
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article
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aside
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details
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dialog
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figcaption
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figure
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footer
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header
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main
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nav
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section
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]
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def block?(node)
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return false if !node
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node.description&.block? || HTML5_BLOCK_ELEMENTS.include?(node.name)
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end
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def fragment_document
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@fragment_document ||= Nokogiri::HTML5::DocumentFragment.parse("").document
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end
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def create_element(tag, inner_html = nil, attributes = {})
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element = fragment_document.create_element(tag, nil, attributes)
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element.inner_html = inner_html if inner_html
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element
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end
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end
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