
from xml.sax.saxutils import XMLGenerator
from xml.dom import XML_NAMESPACE
from xml.sax.xmlreader import AttributesNSImpl

from rdflib.compat import etree

from rdflib import Literal, URIRef, BNode, Graph, Variable
from rdflib.query import (
    Result,
    ResultParser,
    ResultSerializer,
    ResultException
)

SPARQL_XML_NAMESPACE = u'http://www.w3.org/2005/sparql-results#'
RESULTS_NS_ET = '{%s}' % SPARQL_XML_NAMESPACE


"""A Parser for SPARQL results in XML:

http://www.w3.org/TR/rdf-sparql-XMLres/

Bits and pieces borrowed from:
http://projects.bigasterisk.com/sparqlhttp/

Authors: Drew Perttula, Gunnar Aastrand Grimnes
"""


class XMLResultParser(ResultParser):

    def parse(self, source):
        return XMLResult(source)


class XMLResult(Result):
    def __init__(self, source):

        xmlstring = source.read()

        if isinstance(xmlstring, unicode):
            xmlstring = xmlstring.encode('utf-8')
        try:
            tree = etree.fromstring(xmlstring)
        except Exception, e:
            try:
                raise e.__class__("error parsing %r: %s" % (xmlstring, e))
            except:
                raise e

        boolean = tree.find(RESULTS_NS_ET + 'boolean')
        results = tree.find(RESULTS_NS_ET + 'results')

        if boolean is not None:
            type_ = 'ASK'
        elif results is not None:
            type_ = 'SELECT'
        else:
            g = Graph()
            try:
                g.parse(data=xmlstring)
                if len(g) == 0:
                    raise
                type_ = 'CONSTRUCT'

            except:
                raise ResultException(
                    "No RDF Graph, result-bindings or boolean answer found!")

        Result.__init__(self, type_)
        if type_ == 'SELECT':
            self.bindings = []
            for result in results:
                r = {}
                for binding in result:
                    r[Variable(binding.get('name'))] = parseTerm(binding[0])
                self.bindings.append(r)

            self.vars = [Variable(x.get("name"))
                         for x in tree.findall(
                         './%shead/%svariable' % (
                             RESULTS_NS_ET, RESULTS_NS_ET))]

        elif type_ == 'ASK':
            self.askAnswer = boolean.text.lower().strip() == "true"
        elif type_ == 'CONSTRUCT':
            self.graph = g


def parseTerm(element):
    """rdflib object (Literal, URIRef, BNode) for the given
    elementtree element"""
    tag, text = element.tag, element.text
    if tag == RESULTS_NS_ET + 'literal':
        if text is None:
            text = ''
        datatype = None
        lang = None
        if element.get('datatype', None):
            datatype = URIRef(element.get('datatype'))
        elif element.get("{%s}lang" % XML_NAMESPACE, None):
            lang = element.get("{%s}lang" % XML_NAMESPACE)

        ret = Literal(text, datatype=datatype, lang=lang)

        return ret
    elif tag == RESULTS_NS_ET + 'uri':
        return URIRef(text)
    elif tag == RESULTS_NS_ET + 'bnode':
        return BNode(text)
    else:
        raise TypeError("unknown binding type %r" % element)


class XMLResultSerializer(ResultSerializer):

    def __init__(self, result):
        ResultSerializer.__init__(self, result)

    def serialize(self, stream, encoding="utf-8"):

        writer = SPARQLXMLWriter(stream, encoding)
        if self.result.type == 'ASK':
            writer.write_header([])
            writer.write_ask(self.result.askAnswer)
        else:
            writer.write_header(self.result.vars)
            writer.write_results_header()
            for b in self.result.bindings:
                writer.write_start_result()
                for key, val in b.iteritems():
                    writer.write_binding(key, val)

                writer.write_end_result()

        writer.close()


# TODO: Rewrite with ElementTree?
class SPARQLXMLWriter:
    """
    Python saxutils-based SPARQL XML Writer
    """
    def __init__(self, output, encoding='utf-8'):
        writer = XMLGenerator(output, encoding)
        writer.startDocument()
        writer.startPrefixMapping(u'', SPARQL_XML_NAMESPACE)
        writer.startPrefixMapping(u'xml', XML_NAMESPACE)
        writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'sparql'),
            u'sparql', AttributesNSImpl({}, {}))
        self.writer = writer
        self._output = output
        self._encoding = encoding
        self._results = False

    def write_header(self, allvarsL):
        self.writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'head'),
            u'head', AttributesNSImpl({}, {}))
        for i in xrange(0, len(allvarsL)):
            attr_vals = {
                (None, u'name'): unicode(allvarsL[i]),
            }
            attr_qnames = {
                (None, u'name'): u'name',
            }
            self.writer.startElementNS(
                (SPARQL_XML_NAMESPACE, u'variable'),
                u'variable', AttributesNSImpl(attr_vals, attr_qnames))
            self.writer.endElementNS((SPARQL_XML_NAMESPACE,
                                      u'variable'), u'variable')
        self.writer.endElementNS((SPARQL_XML_NAMESPACE, u'head'), u'head')

    def write_ask(self, val):
        self.writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'boolean'),
            u'boolean', AttributesNSImpl({}, {}))
        self.writer.characters(str(val).lower())
        self.writer.endElementNS(
            (SPARQL_XML_NAMESPACE, u'boolean'), u'boolean')

    def write_results_header(self):
        self.writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'results'),
            u'results', AttributesNSImpl({}, {}))
        self._results = True

    def write_start_result(self):
        self.writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'result'),
            u'result', AttributesNSImpl({}, {}))
        self._resultStarted = True

    def write_end_result(self):
        assert self._resultStarted
        self.writer.endElementNS(
            (SPARQL_XML_NAMESPACE, u'result'), u'result')
        self._resultStarted = False

    def write_binding(self, name, val):
        assert self._resultStarted

        attr_vals = {
            (None, u'name'): unicode(name),
        }
        attr_qnames = {
            (None, u'name'): u'name',
        }
        self.writer.startElementNS(
            (SPARQL_XML_NAMESPACE, u'binding'),
            u'binding', AttributesNSImpl(attr_vals, attr_qnames))

        if isinstance(val, URIRef):
            self.writer.startElementNS(
                (SPARQL_XML_NAMESPACE, u'uri'),
                u'uri', AttributesNSImpl({}, {}))
            self.writer.characters(val)
            self.writer.endElementNS(
                (SPARQL_XML_NAMESPACE, u'uri'), u'uri')
        elif isinstance(val, BNode):
            self.writer.startElementNS(
                (SPARQL_XML_NAMESPACE, u'bnode'),
                u'bnode', AttributesNSImpl({}, {}))
            self.writer.characters(val)
            self.writer.endElementNS(
                (SPARQL_XML_NAMESPACE, u'bnode'), u'bnode')
        elif isinstance(val, Literal):
            attr_vals = {}
            attr_qnames = {}
            if val.language:
                attr_vals[(XML_NAMESPACE, u'lang')] = val.language
                attr_qnames[(XML_NAMESPACE, u'lang')] = u"xml:lang"
            elif val.datatype:
                attr_vals[(None, u'datatype')] = val.datatype
                attr_qnames[(None, u'datatype')] = u'datatype'

            self.writer.startElementNS(
                (SPARQL_XML_NAMESPACE, u'literal'),
                u'literal', AttributesNSImpl(attr_vals, attr_qnames))
            self.writer.characters(val)
            self.writer.endElementNS(
                (SPARQL_XML_NAMESPACE, u'literal'), u'literal')

        else:
            raise Exception("Unsupported RDF term: %s" % val)

        self.writer.endElementNS(
            (SPARQL_XML_NAMESPACE, u'binding'), u'binding')

    def close(self):
        if self._results:
            self.writer.endElementNS(
                (SPARQL_XML_NAMESPACE, u'results'), u'results')
        self.writer.endElementNS(
            (SPARQL_XML_NAMESPACE, u'sparql'), u'sparql')
        self.writer.endDocument()
