npm/marky-markdown

var GithubSlugger = require('github-slugger')
var innertext = require('innertext')
var tokenUtil = require('../token-util')

var headings = module.exports = function (md, options) {
  var headingAnchorClass = options.headingAnchorClass || 'anchor'
  var headingSvgClass = options.headingSvgClass || ['octicon', 'octicon-link']
  var iconClasses = [].concat(headingSvgClass).join(' ')
  // shamelessly borrowed from GitHub, thanks y'all
  var svgLinkIconText = '<svg aria-hidden="true" class="' + iconClasses + '" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg>'
  if (options && !options.prefixHeadingIds) {
    headings.prefix = ''
  } else {
    headings.prefix = headings.prefix || headings.defaultPrefix
  }

  var slugger = new GithubSlugger()
  var Token

  md.core.ruler.push('headingLinks', function (state) {
    // save the Token constructor because we'll be building a few instances at render
    // time; that's sort of outside the intended markdown-it parsing sequence, but
    // since we have tight control over what we're creating (a link), we're safe
    if (!Token) {
      Token = state.Token
      tokenUtil.set(Token)
    }
  })

  md.renderer.rules.heading_open = function (tokens, idx, opts, env, self) {
    var children = tokens[idx + 1].children
    // make sure heading is not empty
    if (children && children.length) {
      // Generate an ID based on the heading's innerHTML; first, render without
      // converting gemoji strings to unicode emoji characters
      var rendered = md.renderer.renderInline(children.map(tokenUtil.unemoji), opts, env)
      var postfix = slugger.slug(
        innertext(rendered)
          .replace(/[<>]/g, '') // In case the heading contains `<stuff>`
          .toLowerCase() // because `slug` doesn't lowercase
      )

      // add 3 new token objects link_open, text, link_close
      var linkOpen = new Token('link_open', 'a', 1)
      var text = new Token('html_inline', '', 0)
      if (options && options.enableHeadingLinkIcons) {
        text.content = svgLinkIconText
      }
      var linkClose = new Token('link_close', 'a', -1)

      // add some link attributes
      linkOpen.attrSet('id', headings.prefix + postfix)
      linkOpen.attrSet('class', headingAnchorClass)
      linkOpen.attrSet('href', '#' + postfix)
      linkOpen.attrSet('aria-hidden', 'true')

      // add new token objects as children of heading
      children.unshift(linkClose)
      children.unshift(text)
      children.unshift(linkOpen)
    }

    return md.renderer.renderToken(tokens, idx, options, env, self)
  }
}

headings.defaultPrefix = 'user-content-'