module.exports = function count_chars(str, mode) {
  //  discuss at: https://locutus.io/php/count_chars/
  // original by: Ates Goral (https://magnetiq.com)
  // improved by: Jack
  // bugfixed by: Onno Marsman (https://twitter.com/onnomarsman)
  // bugfixed by: Kevin van Zonneveld (https://kvz.io)
  //    input by: Brett Zamir (https://brett-zamir.me)
  //  revised by: Theriault (https://github.com/Theriault)
  //   example 1: count_chars("Hello World!", 3)
  //   returns 1: " !HWdelor"
  //   example 2: count_chars("Hello World!", 1)
  //   returns 2: {32:1,33:1,72:1,87:1,100:1,101:1,108:3,111:2,114:1}

  const result = {}
  const resultArr = []
  let i

  str = ('' + str)
    .split('')
    .sort()
    .join('')
    .match(/(.)\1*/g)

  if ((mode & 1) === 0) {
    for (i = 0; i !== 256; i++) {
      result[i] = 0
    }
  }

  if (mode === 2 || mode === 4) {
    for (i = 0; i !== str.length; i += 1) {
      delete result[str[i].charCodeAt(0)]
    }
    for (i in result) {
      result[i] = mode === 4 ? String.fromCharCode(i) : 0
    }
  } else if (mode === 3) {
    for (i = 0; i !== str.length; i += 1) {
      result[i] = str[i].slice(0, 1)
    }
  } else {
    for (i = 0; i !== str.length; i += 1) {
      result[str[i].charCodeAt(0)] = str[i].length
    }
  }
  if (mode < 3) {
    return result
  }

  for (i in result) {
    resultArr.push(result[i])
  }

  return resultArr.join('')
}