Decoding HTML Entities - Swift 3

// Vladimir Zhelnov - neatek.pw - Web/iOS dev
extension String {
    var stringByDecodingHTMLEntities : String {
        func decodeNumeric(_ string : String, base : Int) -> Character? {
            guard let code = UInt32(string, radix: base),
                let uniScalar = UnicodeScalar(code) else { return nil }
            return Character(uniScalar)
        }
        func decode(_ entity : String) -> Character? {
            if entity.hasPrefix("&#x") || entity.hasPrefix("&#X"){
                return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 3) ..< entity.index(entity.endIndex, offsetBy: -1)), base: 16)
            } else if entity.hasPrefix("&#") {
                return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 2) ..< entity.index(entity.endIndex, offsetBy: -1)), base: 10)
            } else {
                return characterEntities[entity]
            }
        }
        var result = ""
        var position = startIndex
        while let ampRange = self.range(of: "&", range: position ..< endIndex) {
            result.append(self[position ..< ampRange.lowerBound])
            position = ampRange.lowerBound
            if let semiRange = self.range(of: ";", range: position ..< endIndex) {
                let entity = self[position ..< semiRange.upperBound]
                position = semiRange.upperBound
                if let decoded = decode(entity) {
                    result.append(decoded)
                } else {
                    result.append(entity)
                }
            } else {
                break
            }
        }
        result.append(self[position ..< endIndex])
        return result
    }
// usage: <string>.stringByDecodingHTMLEntities