parseFile.ts

import fs from 'fs/promises';
import path from 'path';

// Linux new line is just \n, Windows it's \n\r and MacOS is \r
const OS = process.platform;

const SPLIT_SCHEME: Record<string, string> = {
  linux: '\n',
  darwin: '\r',
  win32: '\r\n',
};
export const newlineSplit = SPLIT_SCHEME[OS];

const parseFile = async (day: number, parser: (input: string, newlineSplit: string) => any): Promise<any> => {
  if (!day) {
    throw new Error('You must enter a day!');
  } else if (day < 1 || day > 31) {
    throw new Error(`There are not ${day} days in December!`);
  }

  try {
    const result = await fs.readFile(path.join(process.cwd(), `day-${day}`, 'input.txt'), { encoding: 'utf-8' });
    return parser(result, newlineSplit);
  } catch (err) {
    throw new Error(`Something went wrong reading the file! Error: \n${err}`);
  }
};

export default parseFile;