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require 'html/pipeline/filter'
module Banzai
module Filter
# HTML filter that adds an anchor child element to all Headers in a
# document, so that they can be linked to.
#
# Generates the Table of Contents with links to each header. See Results.
#
# Based on HTML::Pipeline::TableOfContentsFilter.
#
# Context options:
# :no_header_anchors - Skips all processing done by this filter.
#
# Results:
# :toc - String containing Table of Contents data as a `ul` element with
# `li` child elements.
class TableOfContentsFilter < HTML::Pipeline::Filter
PUNCTUATION_REGEXP = /[^\p{Word}\- ]/u
def call
return doc if context[:no_header_anchors]
result[:toc] = ""
add_header_anchors
result[:toc] = %Q{<ul class="section-nav">\n#{result[:toc]}</ul>} unless result[:toc].empty?
replace_toc_tag
doc
end
private
def add_header_anchors
headers = Hash.new(0)
doc.css('h1, h2, h3, h4, h5, h6').each do |node|
text = node.text
id = text.downcase
id.gsub!(PUNCTUATION_REGEXP, '') # remove punctuation
id.tr!(' ', '-') # replace spaces with dash
id.squeeze!('-') # replace multiple dashes with one
uniq = (headers[id] > 0) ? "-#{headers[id]}" : ''
headers[id] += 1
if header_content = node.children.first
href = "#{id}#{uniq}"
push_toc(href, text)
header_content.add_previous_sibling(anchor_tag(href))
end
end
end
def anchor_tag(href)
%Q{<a id="#{href}" class="anchor" href="##{href}" aria-hidden="true"></a>}
end
def push_toc(href, text)
result[:toc] << %Q{<li><a href="##{href}">#{text}</a></li>\n}
end
def replace_toc_tag
search_text_nodes(doc).each do |node|
if toc_tag?(node)
process_toc_tag(node)
end
end
end
# A Gollum-compatible ToC tag is `[[_TOC_]]`, but due to MarkdownFilter
# running before this one, it will be converted into `[[<em>TOC</em>]]`
def toc_tag?(node)
node.content == 'TOC' &&
node.parent.name == 'em' &&
node.parent.parent.text == '[[TOC]]'
end
# Replace an entire `[[<em>TOC</em>]]` node with our result
def process_toc_tag(node)
node.parent.parent.replace(result[:toc].presence || '')
end
end
end
end
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