from rdflib.term import _PLAIN_LITERAL_TYPES, Literal


def _literal_n3(self, use_plain=False, qname_callback=None):
    if use_plain and self.datatype in _PLAIN_LITERAL_TYPES:
        try:
            self.toPython()  # check validity
            # py3 makes %s give much nicer presentations
            return '%s' % self
        except ValueError:
            pass  # if it's in, we let it out?

    encoded = self._quote_encode()

    datatype = self.datatype
    quoted_dt = None
    if datatype:
        if qname_callback:
            quoted_dt = qname_callback(datatype)
        if not quoted_dt:
            quoted_dt = "<%s>" % datatype

    language = self.language
    if language:
        if datatype:
            # TODO: this isn't valid RDF (it's datatype XOR language)
            return '%s@%s^^%s' % (encoded, language, quoted_dt)
        return '%s@%s' % (encoded, language)
    elif datatype:
        return '%s^^%s' % (encoded, quoted_dt)
    else:
        return '%s' % encoded


def patch():
    Literal._literal_n3 = _literal_n3