split_by_abc.js

'use strict';
/******************************************************************************/
const path = process.argv[2];
if (!path) {
  console.log('Add the file path, please.');
  process.exit();
}
/******************************************************************************/
const fs = require('fs');

const encoding = 'utf8'; //ascii utf8 utf16le

const rl = require('readline').createInterface({
  input: fs.createReadStream(path, encoding),
  terminal: false,
  historySize: 0
});

const logFile = fs.openSync(path.replace(/(\.[^.]+)?$/, '.-split_log$1'), 'w');
fs.writeSync(logFile, '\uFEFF', null, encoding);

const abc = Array.from('ABCDEFGHIJKLMNOPQRSTUVWXYZ´');
const formatNumberRE = /\B(?=(?:\d{3})+$)/g;

let   outFile;
let   lines;
let   nextChr;
let   nextChrRE;
/******************************************************************************/
newPart(abc.shift());
/******************************************************************************/
rl.on('line', line => {
  if (nextChr && nextChrRE.test(line)) {
    newPart(nextChr);
  }
  fs.writeSync(outFile, `${line}\n`, null, encoding);
  lines++;
}).on('close', () => {
  fs.closeSync(outFile);
  fs.writeSync(logFile,
    `${lines.toString().replace(formatNumberRE, ' ')}\n`, null, encoding);
  fs.closeSync(logFile);
});
/******************************************************************************/
function newPart(chr) {
  if(outFile) {
    fs.closeSync(outFile);
    fs.writeSync(logFile,
      `${lines.toString().replace(formatNumberRE, ' ')}\n`, null, encoding);
  }
  lines = 0;
  outFile = fs.openSync(path.replace(/(\.[^.]+)?$/, `.${chr}$1`), 'w');
  if (chr !== 'A') fs.writeSync(outFile, '\uFEFF', null, encoding);
  console.log(chr);
  fs.writeSync(logFile, `${chr}: `, null, encoding);
  if(nextChr = abc.shift()) nextChrRE = new RegExp(`^• ${nextChr}`, 'i');
}
/******************************************************************************/