module.exports = function quoted_printable_encode(str) {
  //  discuss at: https://locutus.io/php/quoted_printable_encode/
  // original by: Theriault (https://github.com/Theriault)
  // improved by: Brett Zamir (https://brett-zamir.me)
  // improved by: Theriault (https://github.com/Theriault)
  //   example 1: quoted_printable_encode('a=b=c')
  //   returns 1: 'a=3Db=3Dc'
  //   example 2: quoted_printable_encode('abc   \r\n123   \r\n')
  //   returns 2: 'abc  =20\r\n123  =20\r\n'
  //   example 3: quoted_printable_encode('0123456789012345678901234567890123456789012345678901234567890123456789012345')
  //   returns 3: '012345678901234567890123456789012345678901234567890123456789012345678901234=\r\n5'
  //        test: skip-2

  const hexChars = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F']
  const RFC2045Encode1IN = / \r\n|\r\n|[^!-<>-~ ]/gm
  const RFC2045Encode1OUT = function (sMatch) {
    // Encode space before CRLF sequence to prevent spaces from being stripped
    // Keep hard line breaks intact; CRLF sequences
    if (sMatch.length > 1) {
      return sMatch.replace(' ', '=20')
    }
    // Encode matching character
    const chr = sMatch.charCodeAt(0)
    return '=' + hexChars[(chr >>> 4) & 15] + hexChars[chr & 15]
  }

  // Split lines to 75 characters; the reason it's 75 and not 76 is because softline breaks are
  // preceeded by an equal sign; which would be the 76th character. However, if the last line/string
  // was exactly 76 characters, then a softline would not be needed. PHP currently softbreaks
  // anyway; so this function replicates PHP.

  const RFC2045Encode2IN = /.{1,72}(?!\r\n)[^=]{0,3}/g
  const RFC2045Encode2OUT = function (sMatch) {
    if (sMatch.substr(sMatch.length - 2) === '\r\n') {
      return sMatch
    }
    return sMatch + '=\r\n'
  }

  str = str.replace(RFC2045Encode1IN, RFC2045Encode1OUT).replace(RFC2045Encode2IN, RFC2045Encode2OUT)

  // Strip last softline break
  return str.substr(0, str.length - 3)
}