reading_progress.js

'use strict';
/******************************************************************************/
const hrstart = process.hrtime();

const fs = require('fs');
const readline = require('readline');
const getByteLength = Buffer.byteLength;

const inputPath  = process.argv[2];
const outputPath = process.argv[3];

if (!inputPath || !outputPath) {
  console.error('Enter the input and output file paths, please.');
  process.exit();
}

try {
  fs.accessSync(inputPath);
} catch(e) {
  console.error('Input file not found.');
  process.exit();
}

const fileSize  = fs.statSync(inputPath)['size'];
let   lineCount = 0;
let   byteCount = 0;

const parser = readline.createInterface({
  input: fs.createReadStream(inputPath, 'utf8'),
  terminal: false,
  historySize: 0
});

const outputFile = fs.openSync(outputPath, 'w');
/******************************************************************************/
fs.writeSync(outputFile, '\uFEFF', null, 'utf8');

console.log('');
const updater = setInterval(updateProgressBar, 500);
/******************************************************************************/
parser.on('line', line => {
  lineCount++;
  if (lineCount === 1) line = line.replace(/^\uFEFF/, '');
  
  byteCount += getByteLength(line, 'utf8') + 1;
  
  fs.writeSync(outputFile, `${line}\n`, null, 'utf8');
}).on('close', () => {
  clearInterval(updater);
  updateProgressBar();
  
  const hrend = process.hrtime(hrstart);
  console.log(
    `\n\nExecution time: ${ hrend[0] }.${ Math.floor(hrend[1]/1000000) }\n`
  );
});
/******************************************************************************/
function updateProgressBar() {
  const readPercent = Math.ceil((byteCount / fileSize) * 100);
  if (readPercent > 100) readPercent = 100;
  
  const barsNumber = Math.floor(readPercent / 2);
  const padsNumber = 50 - barsNumber;
  
  readline.cursorTo(process.stdout, 0);
  readline.clearLine(process.stdout, 0);
  process.stdout.write(
    `${ '█'.repeat(barsNumber) }${ ' '.repeat(padsNumber) } ${readPercent}%`
  );
}
/******************************************************************************/