A port of the recursive HN comment calculator used in "Asyncio Coroutine Patterns" using Node.js async/await

hnRecursiveComments.js

/**
 * A port of the recursive HN comment calculator used in
 * "Asyncio Coroutine Patterns" using Node.js async/await
 * 
 * Assume we want to calculate the number of comments of a particular post in
 * Hacker News by recursively aggregating the number of descendants.
 * 
 * Original article at:
 * https://medium.com/python-pandemonium/asyncio-coroutine-patterns-beyond-await-a6121486656f
 * 
 * And Python code:
 * https://github.com/yeraydiazdiaz/asyncio-coroutine-patterns/blob/master/01_recursive_coroutines/recursive_coroutines.py
 */

const url = require('url')
const axios = require('axios')
const winston = require('winston')
const ArgumentParser = require('argparse').ArgumentParser

const instance = axios.create({
  baseURL: 'https://hacker-news.firebaseio.com/v0/item/',
  timeout: 5000,
})

/**
 * Fetches a single post by ID.
 * @param {number} id - The post's ID.
 * @return {object} The `data` of the Axios response.
 */
async function fetchPost(id) {
  const start = new Date()
  const response = await instance.get(`${id}.json`)
  const end = new Date()
  winston.debug(
    `Fetching post with ID ${id} took ${(end - start) / 1000} seconds`)
  return response.data
}

/**
 * Calculates the number of comments for a post
 * @param {number} id - The post's ID.
 * @return {number} The number of comments for the post.
 */
async function getNumberOfComments(id) {
  const response = await fetchPost(id)

  if (!response.hasOwnProperty('kids')) return 0

  let numberOfComments = response.kids.length
  const results = await Promise.all(response.kids.map(getNumberOfComments))
  numberOfComments += results.reduce((sum, value) => sum + value)
  winston.debug(`${id} > ${numberOfComments} comments`)
  return numberOfComments
}

/**
 * Gets the post ID from a URL
 * @param {string} URL - The post's URL.
 * @return {int} The post's ID.
 */
function getIDFromURL(URL) {
  const id = url.parse(URL).query.slice(3)
  return parseInt(id)
}

/**
 * Entry point to the script when ran directly in the console
 * @param {object} args - Arguments from `argparse`.
 */
function cli() {
  const parser = new ArgumentParser({
    addHelp: true,
    description: 'Recursive HN comment calculator using Node.js async/await',
  })
  parser.addArgument('--id', {
    help: 'ID of the post in HN, defaults to 8863',
    type: 'int',
    defaultValue: 8863,
  })
  parser.addArgument('--url', {
    help: 'URL of a post in HN, use instead of `id`',
    type: 'string',
  })
  parser.addArgument('-v', {
    help: 'Verbose output`',
    action: 'storeTrue',
  })
  const args = parser.parseArgs()
  if (!args.id && !args.url) {
    throw new Error('Too few arguments, please use either `id` or `url`')
  }
  winston.level = args.v ? 'debug' : 'info'
  const id = args.url ? getIDFromURL(args.url) : args.id
  winston.info(`Calculating comments for post ${id}`)
  const start = new Date()
  getNumberOfComments(id)
    .then((res) => {
      const elapsed = (new Date().getTime() - start.getTime()) / 1000
      winston.info(`Number of comments: ${res}, took: ${elapsed} seconds`)
    })
    .catch((error) => winston.error(error))
}

if (require.main.id === 'module') {
  exports.default = getNumberOfComments
} else {
  cli()
}