utils.js

import { curry, defaultTo, length } from 'ramda';
import { Buffer } from 'buffer'; // Buffer is global in node environment


// stringToBuffer :: String -> String -> Uint8Array
export const stringToBuffer = curry((encoding, string) => Buffer.from(string, encoding));

// toByteRange :: Array -> Array
export const toByteOffset = ([begin, count]) => begin + count;

// toLineNumber :: String -> Number -> String -> Number
export const toLineNumber = curry((encoding, offset, input) => {
  const buffer = stringToBuffer(encoding, input);
  const stringFragment = buffer.toString(encoding, 0, offset);
  const matches = defaultTo([], stringFragment.match(/\n/gm));

  return length(matches) + 1;
});