anchor-markdown-header.js

'use strict';

var emojiRegex = require('emoji-regex');
var removeMd = require('remove-markdown');

// https://github.com/joyent/node/blob/192192a09e2d2e0d6bdd0934f602d2dbbf10ed06/tools/doc/html.js#L172-L183
function getNodejsId(text, repetition) {
  text = text.replace(/[^a-z0-9]+/g, '_');
  text = text.replace(/^_+|_+$/, '');
  text = text.replace(/^([^a-z])/, '_$1');

  // If no repetition, or if the repetition is 0 then ignore. Otherwise append '_' and the number.
  // An example may be found here: http://nodejs.org/api/domain.html#domain_example_1
  if (repetition) {
    text += '_' + repetition;
  }

  return text;
}

function basicGithubId(text) {
  return text.replace(/ /g,'-')
    // escape codes
    .replace(/%([abcdef]|\d){2,2}/ig, '')
    // single chars that are removed
    .replace(/[\/\\?!%:\[\]`.,()*"';{}+=<>~\$|#@&–—]/g,'')
    // CJK punctuations that are removed
    .replace(/[。？！，、；：“”【】（）〔〕［］﹃﹄“ ”‘’﹁﹂—…－～《》〈〉「」]/g, '')
    // latin-1 supplement chars that are removed
    .replace(/[¡¢£¤¥¦§¨©«¬®¯°±²³´¶·¸¹»¼½¾¿]/g, '')
    ;

}

function getGithubId(text, repetition) {
  text = basicGithubId(text);

  // If no repetition, or if the repetition is 0 then ignore. Otherwise append '-' and the number.
  if (repetition) {
    text += '-' + repetition;
  }

  // Strip emojis
  text = text.replace(emojiRegex(), '')

  // Strip embedded markdown formatting
  text = removeMd(text)

  return text;
}

function getBitbucketId(text, repetition) {
  text = 'markdown-header-' + basicGithubId(text);

  // BitBucket condenses consecutive hyphens (GitHub doesn't)
  text = text.replace(/--+/g, '-');

  // If no repetition, or if the repetition is 0 then ignore. Otherwise append '_' and the number.
  // https://groups.google.com/d/msg/bitbucket-users/XnEWbbzs5wU/Fat0UdIecZkJ
  if (repetition) {
    text += '_' + repetition;
  }

  return text;
}

function basicGhostId(text) {
  return text.replace(/ /g,'')
    // escape codes are not removed
    // single chars that are removed
    .replace(/[\/?:\[\]`.,()*"';{}\-+=<>!@#%^&\\\|]/g,'')
    // $ replaced with d
    .replace(/\$/g, 'd')
    // ~ replaced with t
    .replace(/~/g, 't')
    ;
}

function getGhostId(text, repetition) {
  text = basicGhostId(text);

  // If no repetition, or if the repetition is 0 then ignore. Otherwise append '-' and the number.
  if (repetition) {
    text += '-' + repetition;
  }

  return text;
}

// see: https://github.com/gitlabhq/gitlabhq/blob/master/doc/user/markdown.md#header-ids-and-links
function getGitlabId(text, repetition) {
  text = text
    .replace(/<(.*)>(.*)<\/\1>/g,"$2") // html tags
    .replace(/!\[.*\]\(.*\)/g,'')      // image tags
    .replace(/\[(.*)\]\(.*\)/,"$1")    // url
    .replace(/\s+/g, '-')              // All spaces are converted to hyphens
    .replace(/[\/?!:\[\]`.,()*"';{}+=<>~\$|#@]/g,'') // All non-word text (e.g., punctuation, HTML) is removed
    .replace(/[。？！，、；：“”【】（）〔〕［］﹃﹄“ ”‘’﹁﹂—…－～《》〈〉「」]/g, '') // remove CJK punctuations
    .replace(/[¹²³]/g, '') // remove snall subset of latin-1 supplement chars
    .replace(/[-]+/g,'-')              // duplicated hyphen
    .replace(/^-/,'')                  // ltrim hyphen
    .replace(/-$/,'');                 // rtrim hyphen
  // If no repetition, or if the repetition is 0 then ignore. Otherwise append '-' and the number.
  if (repetition) {
    text += '-' + repetition;
  }
  return text;
}


/**
 * Generates an anchor for the given header and mode.
 *
 * @name anchorMarkdownHeader
 * @function
 * @param header      {String} The header to be anchored.
 * @param mode        {String} The anchor mode (github.com|nodejs.org|bitbucket.org|ghost.org|gitlab.com).
 * @param repetition  {Number} The nth occurrence of this header text, starting with 0. Not required for the 0th instance.
 * @param href        {String} The href to be used in the anchor.
 * @return            {String} The header anchor that is compatible with the given mode.
 */
module.exports = function anchorMarkdownHeader(header, mode, repetition, href) {
  mode = mode || 'github.com';
  var replace;
  var customEncodeURI = encodeURI;
  var customCasing = asciiOnlyToLowerCase;

  // Extended Markdown heading IDs: `Header text {#id}` or kramdown's `{:#id}` at end of line.
  // See https://www.markdownlang.com/extended/heading-ids.html
  var idMatch = header.match(/^(.*?)[ \t]*\{:?#([^\s}]+)\}[ \t]*$/);
  if (idMatch) {
    header = idMatch[1];
    href = idMatch[2];
  }

  switch(mode) {
    case 'github.com':
      replace = getGithubId;
      customEncodeURI = function(uri) {
        var newURI = encodeURI(uri);

        // encodeURI replaces the zero width joiner character
        // (used to generate emoji sequences, e.g.Female Construction Worker 👷🏼‍♀️)
        // github doesn't URL encode them, so we replace them after url encoding to preserve the zwj character.
        return newURI.replace(/%E2%80%8D/g, '\u200D');
      };
      customCasing = function(input) {
        // GitHub prefers to lowercase all characters, not just ASCII ones. Previously this was not the case.
        return input.toLowerCase();
      }
      break;
    case 'bitbucket.org':
      replace = getBitbucketId;
      break;
    case 'gitlab.com':
      replace = getGitlabId;
      break;
    case 'nodejs.org':
      replace = getNodejsId;
      break;
    case 'ghost.org':
      replace = getGhostId;
      break;
    case 'custom':
      if(href === undefined){
        throw new Error('Missing href');
      }
      break;
    default:
      throw new Error('Unknown mode: ' + mode);
  }

  function asciiOnlyToLowerCase(input) {
    var result = '';
    for (var i = 0; i < input.length; ++i) {
      if (input[i] >= 'A' && input[i] <= 'Z') {
        result += input[i].toLowerCase();
      } else {
        result += input[i];
      }
    }
    return result;
  }

  href = href || replace(customCasing(header.trim()), repetition);

  return '[' + header + '](#' + customEncodeURI(href) + ')';
};