"""SPARQL -> RQL translator

:organization: Logilab

: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

def order_limit_offset(sparqlst):

    addons = ''

    if sparqlst.orderby:

        sortterms = ', '.join('%s %s' % (var.name.upper(), ascdesc.upper())

                              for var, ascdesc in sparqlst.orderby)

        addons += ' ORDERBY %s' % sortterms

    if sparqlst.limit:

        addons += ' LIMIT %s' % sparqlst.limit

    if sparqlst.offset:

        addons += ' OFFSET %s' % sparqlst.offset

    return addons

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 = []

        self.literals = {}

        self._litcount = 0

    def add_literal(self, value):

        key = chr(ord('a') + self._litcount)

        self._litcount += 1

        self.literals[key] = value

        return key

    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

    def build_restrictions(self):

        # now, for each predicate

        for yams_predicates, subjvar, obj in self.infer_types_info:

            rel = yams_predicates[0]

            # 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, obj))

                    break

            # else we can simply add it to base rql restrictions

            else:

                restr = self.build_restriction(subjvar, rel[1], obj)

                self.restrictions.append(restr)

    def build_restriction(self, subjvar, rtype, obj):

        if isinstance(obj, ast.SparqlLiteral):

            key = self.add_literal(obj.value)

            objvar = '%%(%s)s' % key

        else:

            assert isinstance(obj, ast.SparqlVar)

            # make a valid rql var name

            objvar = obj.name.upper()

        # else we can simply add it to base rql restrictions

        return '%s %s %s' % (subjvar, rtype, objvar)

    def finalize(self):

        """return corresponding rql query (string) / args (dict)"""

        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, obj in self.union_params:

            thisunions = []

            for st, rt, ot in releq:

                thisunions.append([self.build_restriction(subjvar, rt, obj)])

                if st != '*':

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

                if isinstance(obj, ast.SparqlVar) and ot != '*':

                    objvar = obj.name.upper()

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

            if not unions:

                unions = thisunions

            else:

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

        selection = 'Any ' + ', '.join(self.selection)

        sparqlst = self.sparqlst

        if sparqlst.distinct:

            selection = 'DISTINCT ' + selection

        if unions:

            baserql = '%s WHERE %s' % (selection, ', '.join(self.restrictions))

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

                    for unionrestrs in unions]

            rql = ' UNION '.join(rqls)

            if sparqlst.orderby or sparqlst.limit or sparqlst.offset:

                rql = '%s%s WITH %s BEING (%s)' % (

                    selection, order_limit_offset(sparqlst),

                    ', '.join(self.selection), rql)

        else:

            rql = '%s%s WHERE %s' % (selection, order_limit_offset(sparqlst),

                                      ', '.join(self.restrictions))

        return rql, self.literals

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 not isinstance(obj, (ast.SparqlLiteral, ast.SparqlVar)):

                    raise UnsupportedQuery()

        qi.infer_types()

        qi.build_restrictions()

        return qi