askirmas / postcss-d-ts

import {promisify} from "util"

import {createReadStream, open, writeFile, close, truncate } from 'fs'

import {createInterface} from 'readline'

import { $exists } from "./utils"

const $open = promisify(open)

, $write = promisify(writeFile)

, $truncate = promisify(truncate)

, $close = promisify(close)

export = rewrite

// TODO #12 with .trim() https://jsbench.me/fykmaajqmc/

async function rewrite(filename: string, lines: string[], eol: string, checkMode: boolean) {

  const {length} = lines

  , {length: eolLength} = eol

  , fileExists = await $exists(filename)

  let row = 0

  , position = 0

  if (fileExists) {

    const lineReader = createInterface({

      input: createReadStream(filename),

      crlfDelay: Infinity,

      historySize: 0

    })

    let isSame = true

    for await (const line of lineReader) {

      if (line !== lines[row]) {

        isSame = false

        continue

      }

      row++

      position += line.length

    }

    lineReader.close()

    if (isSame) {

      if (lines[row] === "")

        row++

      if (length === row)

        return

    }

    !checkMode && await $truncate(filename, position + eolLength * (row - 1))

  }

  if (checkMode)

    throw Error(`Content of "${filename}" should be another`)

  const fd = await $open(filename, "a")

  for (let i = row; i < length; i++)

    await $write(fd, `${

      i ? eol : ''

    }${

      lines[i]

    }`)

  await $close(fd)

}