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# frozen_string_literal: true
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] = +""
headers = Hash.new(0)
header_root = current_header = HeaderNode.new
doc.css('h1, h2, h3, h4, h5, h6').each do |node|
if header_content = node.children.first
id = node
.text
.downcase
.gsub(PUNCTUATION_REGEXP, '') # remove punctuation
.tr(' ', '-') # replace spaces with dash
.squeeze('-') # replace multiple dashes with one
.gsub(/\A(\d+)\z/, 'anchor-\1') # digits-only hrefs conflict with issue refs
uniq = headers[id] > 0 ? "-#{headers[id]}" : ''
headers[id] += 1
href = "#{id}#{uniq}"
current_header = HeaderNode.new(node: node, href: href, previous_header: current_header)
header_content.add_previous_sibling(anchor_tag(href))
end
end
push_toc(header_root.children, root: true)
doc
end
private
def anchor_tag(href)
%Q{<a id="user-content-#{href}" class="anchor" href="##{href}" aria-hidden="true"></a>}
end
def push_toc(children, root: false)
return if children.empty?
klass = ' class="section-nav"' if root
result[:toc] << "<ul#{klass}>"
children.each { |child| push_anchor(child) }
result[:toc] << '</ul>'
end
def push_anchor(header_node)
result[:toc] << %Q{<li><a href="##{header_node.href}">#{header_node.text}</a>}
push_toc(header_node.children)
result[:toc] << '</li>'
end
class HeaderNode
attr_reader :node, :href, :parent, :children
def initialize(node: nil, href: nil, previous_header: nil)
@node = node
@href = href
@children = []
@parent = find_parent(previous_header)
@parent.children.push(self) if @parent
end
def level
return 0 unless node
@level ||= node.name[1].to_i
end
def text
return '' unless node
@text ||= EscapeUtils.escape_html(node.text)
end
private
def find_parent(previous_header)
return unless previous_header
if level == previous_header.level
parent = previous_header.parent
elsif level > previous_header.level
parent = previous_header
else
parent = previous_header
parent = parent.parent while parent.level >= level
end
parent
end
end
end
end
end
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