"""SPARQL -> RQL translator

:organization: Logilab

:copyright: 2009 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.

:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr

:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses

"""

from logilab.common import make_domains

from rql import TypeResolverException

from fyzz.yappsparser import parse

from fyzz import ast

from cubicweb.xy import xy

class UnsupportedQuery(Exception): pass

class QueryInfo(object):

    """wrapper class containing necessary information to generate a RQL query

    from a sparql syntax tree

    """

    def __init__(self, sparqlst):

        self.sparqlst = sparqlst

        if sparqlst.selected == ['*']:

            self.selection = [var.upper() for var in sparqlst.variables]

        else:

            self.selection = [var.name.upper() for var in sparqlst.selected]

        self.possible_types = {}

        self.infer_types_info = []

        self.union_params = []

        self.restrictions = []

    def finalize(self):

        """return corresponding rql query"""

        for varname, ptypes in self.possible_types.iteritems():

            if len(ptypes) == 1:

                self.restrictions.append('%s is %s' % (varname, iter(ptypes).next()))

        unions = []

        for releq, subjvar, objvar in self.union_params:

            thisunions = []

            for st, rt, ot in releq:

                thisunions.append(['%s %s %s' % (subjvar, rt, objvar)])

                if st != '*':

                    thisunions[-1].append('%s is %s' % (subjvar, st))

                if ot != '*':

                    thisunions[-1].append('%s is %s' % (objvar, ot))

            if not unions:

                unions = thisunions

            else:

                unions = zip(*make_domains([unions, thisunions]))

        if not unions:

        rqls = ['(%s, %s)' % (baserql, ', '.join(unionrestrs))

                for unionrestrs in unions]

    def set_possible_types(self, var, varpossibletypes):

        """set/restrict possible types for the given variable.

        :return: True if something changed, else false.

        :raise: TypeResolverException if no more type allowed

        """

        varpossibletypes = set(varpossibletypes)

        try:

            ctypes = self.possible_types[var]

            nbctypes = len(ctypes)

            ctypes &= varpossibletypes

            if not ctypes:

                raise TypeResolverException()

            return len(ctypes) != nbctypes

        except KeyError:

            self.possible_types[var] = varpossibletypes

            return True

    def infer_types(self):

        # XXX should use something similar to rql.analyze for proper type inference

        modified = True

        # loop to infer types until nothing changed

        while modified:

            modified = False

            for yams_predicates, subjvar, obj in self.infer_types_info:

                nbchoices = len(yams_predicates)

                # get possible types for the subject variable, according to the

                # current predicate

                svptypes = set(s for s, r, o in yams_predicates)

                if not '*' in svptypes:

                    if self.set_possible_types(subjvar, svptypes):

                        modified = True

                # restrict predicates according to allowed subject var types

                if subjvar in self.possible_types:

                    yams_predicates = [(s, r, o) for s, r, o in yams_predicates

                                       if s == '*' or s in self.possible_types[subjvar]]

                if isinstance(obj, ast.SparqlVar):

                    # make a valid rql var name

                    objvar = obj.name.upper()

                    # get possible types for the object variable, according to

                    # the current predicate

                    ovptypes = set(o for s, r, o in yams_predicates)

                    if not '*' in ovptypes:

                        if self.set_possible_types(objvar, ovptypes):

                            modified = True

                    # restrict predicates according to allowed object var types

                    if objvar in self.possible_types:

                        yams_predicates = [(s, r, o) for s, r, o in yams_predicates

                                           if o == '*' or o in self.possible_types[objvar]]

                # ensure this still make sense

                if not yams_predicates:

                    raise TypeResolverException()

                if len(yams_predicates) != nbchoices:

                    modified = True

        # now, for each predicate

        for yams_predicates, subjvar, obj in self.infer_types_info:

            rel = yams_predicates[0]

            objvar = obj.name.upper()

            # if there are several yams relation type equivalences, we will have

            # to generate several unioned rql queries

            for s, r, o in yams_predicates[1:]:

                if r != rel[1]:

                    self.union_params.append((yams_predicates, subjvar, objvar))

                    break

            else:

                # else we can simply add it to base rql restrictions

                self.restrictions.append('%s %s %s' % (subjvar, rel[1], objvar))

class Sparql2rqlTranslator(object):

    def __init__(self, yschema):

        self.yschema = yschema

    def translate(self, sparql):

        sparqlst = parse(sparql)

        if sparqlst.type != 'select':

            raise UnsupportedQuery()

        qi = QueryInfo(sparqlst)

        for subj, predicate, obj in sparqlst.where:

            if not isinstance(subj, ast.SparqlVar):

                raise UnsupportedQuery()

            # make a valid rql var name

            subjvar = subj.name.upper()

            if predicate == ('', 'a'):

                # special 'is' relation

                if not isinstance(obj, tuple):

                    raise UnsupportedQuery()

                # restrict possible types for the subject variable

                qi.set_possible_types(

                    subjvar, xy.yeq(':'.join(obj), isentity=True))

            else:

                # 'regular' relation (eg not 'is')

                if not isinstance(predicate, tuple):

                    raise UnsupportedQuery()

                # list of 3-uple

                #   (yams etype (subject), yams rtype, yams etype (object))

                # where subject / object entity type may '*' if not specified

                yams_predicates = xy.yeq(':'.join(predicate))

                qi.infer_types_info.append((yams_predicates, subjvar, obj))

                if isinstance(obj, ast.SparqlVar):

                    # make a valid rql var name

                    objvar = obj.name.upper()

                else:

                    raise UnsupportedQuery()

        qi.infer_types()

        return qi