const fs = require('fs')
const memwatch = require('@airbnb/node-memwatch')
const { pipeline } = require('stream/promises')
const { transform } = require('stream-transform')

let maxUsedHeap = 0

async function main() {
  memwatch.on('stats', (stats) => {
    maxUsedHeap = Math.max(maxUsedHeap, stats.used_heap_size)
  })

  await pipeline(
    function* () {
      let i = -1
      const n = 9999999
      while (++i < n) {
        yield { i }
      }
    },
    transform({ parallel: +process.env.PARALLEL }, (chunk, next) =>
      next(null, chunk.i)
    ),
    fs.createWriteStream('/tmp/output')
  )

  console.log(`${maxUsedHeap / (1000 * 1000)}mb`)
}

main()

// $ PARALLEL=1 node example.js
// 6.009856mb

// $ PARALLEL=2 node example.js
// 320.684144mb