Generate table of contents for markdown file

generate-toc.js

'use strict';

const fs = require('fs');
const readline = require('readline');

const filename = process.argv[2];
const stream = fs.createReadStream(filename);
const rl = readline.createInterface({input: stream});
let currentLevel = 0;
const linkRevisions = {};
rl.on('line', (line) => {
  // Skip top header
  if (line.indexOf('##') !== 0) {
    return;
  }

  const match = line.match(/^(#+)\s+([^$]+)\n?$/);
  const offset = '    '.repeat(match[1].length - 2);
  const label = match[2];
  const link = label
    .toLowerCase()
    .replace(/[^a-z0-9\s]/g, '')
    .replace(/[\s]+/g, '-');

  // Every duplicate of some link will have hash with appended dash and
  // duplicate number. I.e. if some section has #link hash, its duplicates will
  // have hashes #link-1, link-2 and so on.
  let linkWithRevision = link;
  if (!linkRevisions[link]) {
    linkRevisions[link] = 1;
  }
  else {
    linkWithRevision = link + '-' + linkRevisions[link];
    ++linkRevisions[link];
  }

  console.log(`${offset}- [${label}](#${linkWithRevision})`);
});