module.exports = function htmlspecialchars(string, quoteStyle, charset, doubleEncode) {
  //       discuss at: https://locutus.io/php/htmlspecialchars/
  //      original by: Mirek Slugen
  //      improved by: Kevin van Zonneveld (https://kvz.io)
  //      bugfixed by: Nathan
  //      bugfixed by: Arno
  //      bugfixed by: Brett Zamir (https://brett-zamir.me)
  //      bugfixed by: Brett Zamir (https://brett-zamir.me)
  //       revised by: Kevin van Zonneveld (https://kvz.io)
  //         input by: Ratheous
  //         input by: Mailfaker (https://www.weedem.fr/)
  //         input by: felix
  // reimplemented by: Brett Zamir (https://brett-zamir.me)
  //           note 1: charset argument not supported
  //        example 1: htmlspecialchars("<a href='test'>Test</a>", 'ENT_QUOTES')
  //        returns 1: '&lt;a href=&#039;test&#039;&gt;Test&lt;/a&gt;'
  //        example 2: htmlspecialchars("ab\"c'd", ['ENT_NOQUOTES', 'ENT_QUOTES'])
  //        returns 2: 'ab"c&#039;d'
  //        example 3: htmlspecialchars('my "&entity;" is still here', null, null, false)
  //        returns 3: 'my &quot;&entity;&quot; is still here'

  let optTemp = 0
  let i = 0
  let noquotes = false
  if (typeof quoteStyle === 'undefined' || quoteStyle === null) {
    quoteStyle = 2
  }
  string = string || ''
  string = string.toString()

  if (doubleEncode !== false) {
    // Put this first to avoid double-encoding
    string = string.replace(/&/g, '&amp;')
  }

  string = string.replace(/</g, '&lt;').replace(/>/g, '&gt;')

  const OPTS = {
    ENT_NOQUOTES: 0,
    ENT_HTML_QUOTE_SINGLE: 1,
    ENT_HTML_QUOTE_DOUBLE: 2,
    ENT_COMPAT: 2,
    ENT_QUOTES: 3,
    ENT_IGNORE: 4,
  }
  if (quoteStyle === 0) {
    noquotes = true
  }
  if (typeof quoteStyle !== 'number') {
    // Allow for a single string or an array of string flags
    quoteStyle = [].concat(quoteStyle)
    for (i = 0; i < quoteStyle.length; i++) {
      // Resolve string input to bitwise e.g. 'ENT_IGNORE' becomes 4
      if (OPTS[quoteStyle[i]] === 0) {
        noquotes = true
      } else if (OPTS[quoteStyle[i]]) {
        optTemp = optTemp | OPTS[quoteStyle[i]]
      }
    }
    quoteStyle = optTemp
  }
  if (quoteStyle & OPTS.ENT_HTML_QUOTE_SINGLE) {
    string = string.replace(/'/g, '&#039;')
  }
  if (!noquotes) {
    string = string.replace(/"/g, '&quot;')
  }

  return string
}