module.exports = function similar_text(first, second, percent) {
  //  discuss at: https://locutus.io/php/similar_text/
  // original by: Rafał Kukawski (https://blog.kukawski.pl)
  // bugfixed by: Chris McMacken
  // bugfixed by: Jarkko Rantavuori original by findings in stackoverflow (https://stackoverflow.com/questions/14136349/how-does-similar-text-work)
  // improved by: Markus Padourek (taken from https://www.kevinhq.com/2012/06/php-similartext-function-in-javascript_16.html)
  //   example 1: similar_text('Hello World!', 'Hello locutus!')
  //   returns 1: 8
  //   example 2: similar_text('Hello World!', null)
  //   returns 2: 0

  if (first === null || second === null || typeof first === 'undefined' || typeof second === 'undefined') {
    return 0
  }

  first += ''
  second += ''

  let pos1 = 0
  let pos2 = 0
  let max = 0
  const firstLength = first.length
  const secondLength = second.length
  let p
  let q
  let l
  let sum

  for (p = 0; p < firstLength; p++) {
    for (q = 0; q < secondLength; q++) {
      for (l = 0; p + l < firstLength && q + l < secondLength && first.charAt(p + l) === second.charAt(q + l); l++) {
        // @todo: ^-- break up this crazy for loop and put the logic in its body
      }
      if (l > max) {
        max = l
        pos1 = p
        pos2 = q
      }
    }
  }

  sum = max

  if (sum) {
    if (pos1 && pos2) {
      sum += similar_text(first.substr(0, pos1), second.substr(0, pos2))
    }

    if (pos1 + max < firstLength && pos2 + max < secondLength) {
      sum += similar_text(
        first.substr(pos1 + max, firstLength - pos1 - max),
        second.substr(pos2 + max, secondLength - pos2 - max),
      )
    }
  }

  if (!percent) {
    return sum
  }

  return (sum * 200) / (firstLength + secondLength)
}