# copyright 2003-2010 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This file is part of CubicWeb.
#
# CubicWeb is free software: you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation, either version 2.1 of the License, or (at your option)
# any later version.
#
# CubicWeb is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License along
# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
"""plan execution of rql queries on multiple sources

the best way to understand what are we trying to acheive here is to read the
unit-tests in unittest_msplanner.py


What you need to know
~~~~~~~~~~~~~~~~~~~~~
1. The system source is expected  to support every entity and relation types

2. Given "X relation Y":

   * if relation, X and Y types are supported by the external source, we suppose
     by default that X and Y should both come from the same source as the
     relation. You can specify otherwise by adding relation into the
     "cross_relations" set in the source's mapping file and it that case, we'll
     consider that we can also find in the system source some relation between
     X and Y coming from different sources.

   * if "relation" isn't supported by the external source but X or Y
     types (or both) are, we suppose by default that can find in the system
     source some relation where X and/or Y come from the external source. You
     can specify otherwise by adding relation into the "dont_cross_relations"
     set in the source's mapping file and it that case, we'll consider that we
     can only find in the system source some relation between X and Y coming
     the system source.


Implementation
~~~~~~~~~~~~~~
XXX explain algorithm


Exemples of multi-sources query execution
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For a system source and a ldap user source (only CWUser and its attributes
is supported, no group or such):

:CWUser X:
1. fetch CWUser X from both sources and return concatenation of results

:CWUser X WHERE X in_group G, G name 'users':
* catch 1
  1. fetch CWUser X from both sources, store concatenation of results into a
     temporary table
  2. return the result of TMP X WHERE X in_group G, G name 'users' from the
     system source
* catch 2
  1. return the result of CWUser X WHERE X in_group G, G name 'users' from system
     source, that's enough (optimization of the sql querier will avoid join on
     CWUser, so we will directly get local eids)

:CWUser X,L WHERE X in_group G, X login L, G name 'users':
1. fetch Any X,L WHERE X is CWUser, X login L from both sources, store
   concatenation of results into a temporary table
2. return the result of Any X, L WHERE X is TMP, X login LX in_group G,
   G name 'users' from the system source


:Any X WHERE X owned_by Y:
* catch 1
  1. fetch CWUser X from both sources, store concatenation of results into a
     temporary table
  2. return the result of Any X WHERE X owned_by Y, Y is TMP from the system
     source
* catch 2
  1. return the result of Any X WHERE X owned_by Y from system source, that's
     enough (optimization of the sql querier will avoid join on CWUser, so we
     will directly get local eids)
"""

__docformat__ = "restructuredtext en"

from itertools import imap, ifilterfalse

from logilab.common.compat import any
from logilab.common.decorators import cached

from rql import BadRQLQuery
from rql.stmts import Union, Select
from rql.nodes import (VariableRef, Comparison, Relation, Constant, Variable,
                       Not, Exists, SortTerm, Function)

from cubicweb import server
from cubicweb.utils import make_uid
from cubicweb.rqlrewrite import add_types_restriction
from cubicweb.server.utils import cleanup_solutions
from cubicweb.server.ssplanner import SSPlanner, OneFetchStep
from cubicweb.server.mssteps import *

Variable._ms_table_key = lambda x: x.name
Relation._ms_table_key = lambda x: x.r_type
# str() Constant.value to ensure generated table name won't be unicode
Constant._ms_table_key = lambda x: str(x.value)

Variable._ms_may_be_processed = lambda x, terms, linkedterms: any(
    t for t in terms if t in linkedterms.get(x, ()))
Relation._ms_may_be_processed = lambda x, terms, linkedterms: all(
    getattr(hs, 'variable', hs) in terms for hs in x.get_variable_parts())

def ms_scope(term):
    rel = None
    scope = term.scope
    if isinstance(term, Variable) and len(term.stinfo['relations']) == 1:
        rel = iter(term.stinfo['relations']).next().relation()
    elif isinstance(term, Constant):
        rel = term.relation()
    elif isinstance(term, Relation):
        rel = term
    if rel is not None and (
        rel.r_type != 'identity' and rel.scope is scope
        and isinstance(rel.parent, Exists) and rel.parent.neged(strict=True)):
        return scope.parent.scope
    return scope

def need_intersect(select, getrschema):
    for rel in select.iget_nodes(Relation):
        if isinstance(rel.parent, Exists) and rel.parent.neged(strict=True) and not rel.is_types_restriction():
            rschema = getrschema(rel.r_type)
            if not rschema.final:
                # if one of the relation's variable is ambiguous but not
                # invariant, an intersection will be necessary
                for vref in rel.get_nodes(VariableRef):
                    var = vref.variable
                    if (var.valuable_references() == 1
                        and len(var.stinfo['possibletypes']) > 1):
                        return True
    return False

def neged_relation(rel):
    parent = rel.parent
    return isinstance(parent, Not) or (isinstance(parent, Exists) and
                                       isinstance(parent.parent, Not))

def need_source_access_relation(vargraph):
    if not vargraph:
        return False
    # check vargraph contains some other relation than the identity relation
    # test of key nature since it may be a variable name (don't care about that)
    # or a 2-uple (var1, var2) associated to the relation to traverse to go from
    # var1 to var2
    return any(key for key, val in vargraph.iteritems()
               if isinstance(key, tuple) and val != 'identity')

def need_aggr_step(select, sources, stepdefs=None):
    """return True if a temporary table is necessary to store some partial
    results to execute the given query
    """
    if len(sources) == 1:
        # can do everything at once with a single source
        return False
    if select.orderby or select.groupby or select.has_aggregat:
        # if more than one source, we need a temp table to deal with sort /
        # groups / aggregat if :
        # * the rqlst won't be splitted (in the other case the last query
        #   using partial temporary table can do sort/groups/aggregat without
        #   the need for a later AggrStep)
        # * the rqlst is splitted in multiple steps and there are more than one
        #   final step
        if stepdefs is None:
            return True
        has_one_final = False
        fstepsolindices = set()
        for stepdef in stepdefs:
            if stepdef[-1]:
                if has_one_final or frozenset(stepdef[2]) != fstepsolindices:
                    return True
                has_one_final = True
            else:
                fstepsolindices.update(stepdef[2])
    return False

def select_group_sort(select): # XXX something similar done in rql2sql
    # add variables used in groups and sort terms to the selection
    # if necessary
    if select.groupby:
        for vref in select.groupby:
            if not vref in select.selection:
                select.append_selected(vref.copy(select))
    for sortterm in select.orderby:
        for vref in sortterm.iget_nodes(VariableRef):
            if not vref in select.get_selected_variables():
                # we can't directly insert sortterm.term because it references
                # a variable of the select before the copy.
                # XXX if constant term are used to define sort, their value
                # may necessite a decay
                select.append_selected(vref.copy(select))
                if select.groupby and not vref in select.groupby:
                    select.add_group_var(vref.copy(select))

def allequals(solutions):
    """return true if all solutions are identical"""
    sol = solutions.next()
    noconstsol = None
    for sol_ in solutions:
        if sol_ != sol:
            return False
    return True

# XXX move functions below to rql ##############################################

def is_ancestor(n1, n2):
    """return True if n2 is a parent scope of n1"""
    p = n1.parent
    while p is not None:
        if p is n2:
            return True
        p = p.parent
    return False

def copy_node(newroot, node, subparts=()):
    newnode = node.__class__(*node.initargs(newroot))
    for part in subparts:
        newnode.append(part)
    return newnode

def used_in_outer_scope(var, scope):
    """return true if the variable is used in an outer scope of the given scope
    """
    for rel in var.stinfo['relations']:
        rscope = ms_scope(rel)
        if not rscope is scope and is_ancestor(scope, rscope):
            return True
    return False

################################################################################

class PartPlanInformation(object):
    """regroups necessary information to execute some part of a "global" rql
    query ("global" means as received by the querier, which may result in
    several internal queries, e.g. parts, due to security insertions). Actually
    a PPI is created for each subquery and for each query in a union.

    It exposes as well some methods helping in executing this part on a
    multi-sources repository, modifying its internal structure during the
    process.

    :attr plan:
      the execution plan
    :attr rqlst:
      the original rql syntax tree handled by this part

    :attr needsplit:
      bool telling if the query has to be split into multiple steps for
      execution or if it can be executed at once

    :attr temptable:
      a SQL temporary table name or None, if necessary to handle aggregate /
      sorting for this part of the query

    :attr finaltable:
      a SQL table name or None, if results for this part of the query should be
      written into a temporary table (usually shared by multiple PPI)

    :attr sourcesterms:
      a dictionary {source : {term: set([solution index, ])}} telling for each
      source which terms are supported for which solutions. A "term" may be
      either a rql Variable, Constant or Relation node.
    """
    def __init__(self, plan, rqlst, rqlhelper=None):
        self.plan = plan
        self.rqlst = rqlst
        self.needsplit = False
        self.temptable = None
        self.finaltable = None
        # shortcuts
        self._schema = plan.schema
        self._session = plan.session
        self._repo = self._session.repo
        self._solutions = rqlst.solutions
        self._solindices = range(len(self._solutions))
        self.system_source = self._repo.system_source
        # source : {term: [solution index, ]}
        self.sourcesterms = self._sourcesterms = {}
        # source : {relation: set(child variable and constant)}
        self._crossrelations = {}
        # dictionary of variables and constants which are linked to each other
        # using a non final relation supported by multiple sources (crossed or
        # not).
        self._linkedterms = {}
        # processing
        termssources = self._compute_sourcesterms()
        self._remove_invalid_sources(termssources)
        self._compute_needsplit()
        # after initialisation, .sourcesterms contains the same thing as
        # ._sourcesterms though during plan construction, ._sourcesterms will
        # be modified while .sourcesterms will be kept unmodified
        self.sourcesterms = {}
        for k, v in self._sourcesterms.iteritems():
            self.sourcesterms[k] = {}
            for k2, v2 in v.iteritems():
                self.sourcesterms[k][k2] = v2.copy()
        # cleanup linked var
        for var, linkedrelsinfo in self._linkedterms.iteritems():
            self._linkedterms[var] = frozenset(x[0] for x in linkedrelsinfo)
        # map output of a step to input of a following step
        self._inputmaps = {}
        # record input map conflicts to resolve them on final step generation
        self._conflicts = []
        if rqlhelper is not None: # else test
            self._insert_identity_variable = rqlhelper._annotator.rewrite_shared_optional
        if server.DEBUG & server.DBG_MS:
            print 'sourcesterms:'
            self._debug_sourcesterms()

    def _debug_sourcesterms(self):
        for source in self._sourcesterms:
            print '-', source
            for term, sols in self._sourcesterms[source].items():
                print '  -', term, id(term), ':', sols

    def copy_solutions(self, solindices):
        return [self._solutions[solidx].copy() for solidx in solindices]

    @property
    @cached
    def part_sources(self):
        if self._sourcesterms:
            return tuple(sorted(self._sourcesterms))
        return (self.system_source,)

    @property
    @cached
    def _sys_source_set(self):
        return frozenset((self.system_source, solindex)
                         for solindex in self._solindices)

    @cached
    def _norel_support_set(self, relation):
        """return a set of (source, solindex) where source doesn't support the
        relation
        """
        return frozenset((source, solidx) for source in self._repo.sources
                         for solidx in self._solindices
                         if not ((source.support_relation(relation.r_type))
                                 or relation.r_type in source.dont_cross_relations))

    def _compute_sourcesterms(self):
        """compute for each term (variable, rewritten constant, relation) and
        for each solution in the rqlst which sources support them
        """
        repo = self._repo
        eschema = self._schema.eschema
        sourcesterms = self._sourcesterms
        # find for each source which variable/solution are supported
        for varname, varobj in self.rqlst.defined_vars.items():
            # if variable has an eid specified, we can get its source directly
            # NOTE: use uidrel and not constnode to deal with "X eid IN(1,2,3,4)"
            if varobj.stinfo['uidrel'] is not None:
                rel = varobj.stinfo['uidrel']
                hasrel = len(varobj.stinfo['relations']) > 1
                for const in rel.children[1].get_nodes(Constant):
                    eid = const.eval(self.plan.args)
                    source = self._session.source_from_eid(eid)
                    if (source is self.system_source
                        or (hasrel and
                            not any(source.support_relation(r.r_type)
                                    for r in varobj.stinfo['relations']
                                    if not r is rel))):
                        self._set_source_for_term(self.system_source, varobj)
                    else:
                        self._set_source_for_term(source, varobj)
                continue
            rels = varobj.stinfo['relations']
            if not rels and varobj.stinfo['typerel'] is None:
                # (rare) case where the variable has no type specified nor
                # relation accessed ex. "Any MAX(X)"
                self._set_source_for_term(self.system_source, varobj)
                continue
            for i, sol in enumerate(self._solutions):
                vartype = sol[varname]
                # skip final variable
                if eschema(vartype).final:
                    break
                for source in repo.sources:
                    if source.support_entity(vartype):
                        # the source support the entity type, though we will
                        # actually have to fetch from it only if
                        # * the variable isn't invariant
                        # * at least one supported relation specified
                        if not varobj._q_invariant or \
                               any(imap(source.support_relation,
                                        (r.r_type for r in rels if r.r_type not in ('identity', 'eid')))):
                            sourcesterms.setdefault(source, {}).setdefault(varobj, set()).add(i)
                        # if variable is not invariant and is used by a relation
                        # not supported by this source, we'll have to split the
                        # query
                        if not varobj._q_invariant and any(ifilterfalse(
                            source.support_relation, (r.r_type for r in rels))):
                            self.needsplit = True
        # add source for rewritten constants to sourcesterms
        self._const_vars = {}
        for vconsts in self.rqlst.stinfo['rewritten'].itervalues():
            # remember those consts come from the same variable
            for const in vconsts:
                self._const_vars[const] = vconsts
            source = self._session.source_from_eid(const.eval(self.plan.args))
            if source is self.system_source:
                for const in vconsts:
                    self._set_source_for_term(source, const)
            elif not self._sourcesterms:
                for const in vconsts:
                    self._set_source_for_term(source, const)
            elif source in self._sourcesterms:
                source_scopes = frozenset(ms_scope(t) for t in self._sourcesterms[source])
                for const in vconsts:
                    if ms_scope(const) in source_scopes:
                        self._set_source_for_term(source, const)
                        # if system source is used, add every rewritten constant
                        # to its supported terms even when associated entity
                        # doesn't actually come from it so we get a changes that
                        # allequals will return True as expected when computing
                        # needsplit
                        # check const is used in a relation restriction
                        if const.relation() and self.system_source in sourcesterms:
                            self._set_source_for_term(self.system_source, const)
        # add source for relations
        rschema = self._schema.rschema
        termssources = {}
        sourcerels = []
        for rel in self.rqlst.iget_nodes(Relation):
            # process non final relations only
            # note: don't try to get schema for 'is' relation (not available
            # during bootstrap)
            if rel.r_type == 'cw_source':
                sourcerels.append(rel)
            elif not (rel.is_types_restriction() or rschema(rel.r_type).final):
                # nothing to do if relation is not supported by multiple sources
                # or if some source has it listed in its cross_relations
                # attribute
                #
                # XXX code below don't deal if some source allow relation
                #     crossing but not another one
                relsources = [s for s in repo.rel_type_sources(rel.r_type)
                               if s is self.system_source
                               or s in self._sourcesterms]
                if len(relsources) < 2:
                    # filter out sources being there because they have this
                    # relation in their dont_cross_relations attribute
                    relsources = [source for source in relsources
                                  if source.support_relation(rel.r_type)]
                    if relsources:
                        # this means the relation is using a variable inlined as
                        # a constant and another unsupported variable, in which
                        # case we put the relation in sourcesterms
                        self._sourcesterms.setdefault(relsources[0], {})[rel] = set(self._solindices)
                    continue
                lhs, rhs = rel.get_variable_parts()
                lhsv, rhsv = getattr(lhs, 'variable', lhs), getattr(rhs, 'variable', rhs)
                # update dictionary of sources supporting lhs and rhs vars
                if not lhsv in termssources:
                    termssources[lhsv] = self._term_sources(lhs)
                if not rhsv in termssources:
                    termssources[rhsv] = self._term_sources(rhs)
                self._handle_cross_relation(rel, relsources, termssources)
                self._linkedterms.setdefault(lhsv, set()).add((rhsv, rel))
                self._linkedterms.setdefault(rhsv, set()).add((lhsv, rel))
        # extract information from cw_source relation
        for srel in sourcerels:
            vref = srel.children[1].children[0]
            sourceeids, sourcenames = [], []
            if isinstance(vref, Constant):
                # simplified variable
                sourceeids = None, (vref.eval(self.plan.args),)
            else:
                var = vref.variable
                for rel in var.stinfo['relations'] - var.stinfo['rhsrelations']:
                    if rel.r_type in ('eid', 'name'):
                        if rel.r_type == 'eid':
                            slist = sourceeids
                        else:
                            slist = sourcenames
                        sources = [cst.eval(self.plan.args)
                                   for cst in rel.children[1].get_nodes(Constant)]
                        if sources:
                            if slist:
                                # don't attempt to do anything
                                sourcenames = sourceeids = None
                                break
                            slist[:] = (rel, sources)
            if sourceeids:
                rel, values = sourceeids
                sourcesdict = self._repo.sources_by_eid
            elif sourcenames:
                rel, values = sourcenames
                sourcesdict = self._repo.sources_by_uri
            else:
                sourcesdict = None
            if sourcesdict is not None:
                lhs = srel.children[0]
                try:
                    sources = [sourcesdict[key] for key in values]
                except KeyError:
                    raise BadRQLQuery('source conflict for term %s' % lhs.as_string())
                if isinstance(lhs, Constant):
                    source = self._session.source_from_eid(lhs.eval(self.plan.args))
                    if not source in sources:
                        raise BadRQLQuery('source conflict for term %s' % lhs.as_string())
                else:
                    lhs = getattr(lhs, 'variable', lhs)
                # XXX NOT NOT
                neged = srel.neged(traverse_scope=True) or (rel and rel.neged(strict=True))
                if neged:
                    for source in sources:
                        self._remove_source_term(source, lhs, check=True)
                else:
                    for source, terms in sourcesterms.items():
                        if lhs in terms and not source in sources:
                            self._remove_source_term(source, lhs, check=True)
                if rel is None:
                    self._remove_source_term(self.system_source, vref)
                    srel.parent.remove(srel)
                elif len(var.stinfo['relations']) == 2 and not var.stinfo['selected']:
                    self._remove_source_term(self.system_source, var)
                    self.rqlst.undefine_variable(var)
        return termssources

    def _handle_cross_relation(self, rel, relsources, termssources):
        for source in relsources:
            if rel.r_type in source.cross_relations:
                ssource = self.system_source
                crossvars = set(x.variable for x in rel.get_nodes(VariableRef))
                for const in rel.get_nodes(Constant):
                    if source.uri != 'system' and not const in self._sourcesterms.get(source, ()):
                        continue
                    crossvars.add(const)
                self._crossrelations.setdefault(source, {})[rel] = crossvars
                if len(crossvars) < 2:
                    # this means there is a constant in the relation which is
                    # not supported by the source, so we can stop here
                    continue
                self._sourcesterms.setdefault(ssource, {})[rel] = set(self._solindices)
                solindices = None
                for term in crossvars:
                    if len(termssources[term]) == 1 and iter(termssources[term]).next()[0].uri == 'system':
                        for ov in crossvars:
                            if ov is not term and (isinstance(ov, Constant) or ov._q_invariant):
                                ssset = frozenset((ssource,))
                                self._remove_sources(ov, termssources[ov] - ssset)
                        break
                    if solindices is None:
                        solindices = set(sol for s, sol in termssources[term]
                                         if s is source)
                    else:
                        solindices &= set(sol for s, sol in termssources[term]
                                          if s is source)
                else:
                    self._sourcesterms.setdefault(source, {})[rel] = solindices

    def _remove_invalid_sources(self, termssources):
        """removes invalid sources from `sourcesterms` member according to
        traversed relations and their properties (which sources support them,
        can they cross sources, etc...)
        """
        for term in self._linkedterms:
            self._remove_sources_until_stable(term, termssources)
        if len(self._sourcesterms) > 1 and hasattr(self.plan.rqlst, 'main_relations'):
            # the querier doesn't annotate write queries, need to do it here
            self.plan.annotate_rqlst()
            # insert/update/delete queries, we may get extra information from
            # the main relation (eg relations to the left of the WHERE
            if self.plan.rqlst.TYPE == 'insert':
                inserted = dict((vref.variable, etype)
                                for etype, vref in self.plan.rqlst.main_variables)
            else:
                inserted = {}
            repo = self._repo
            rschema = self._schema.rschema
            for rel in self.plan.rqlst.main_relations:
                if not rschema(rel.r_type).final:
                    # nothing to do if relation is not supported by multiple sources
                    if len(repo.rel_type_sources(rel.r_type)) < 2:
                        continue
                    lhs, rhs = rel.get_variable_parts()
                    try:
                        lhsv = self._extern_term(lhs, termssources, inserted)
                        rhsv = self._extern_term(rhs, termssources, inserted)
                    except KeyError:
                        continue
                    self._remove_term_sources(lhsv, rel, rhsv, termssources)
                    self._remove_term_sources(rhsv, rel, lhsv, termssources)

    def _extern_term(self, term, termssources, inserted):
        var = term.variable
        if var.stinfo['constnode']:
            termv = var.stinfo['constnode']
            termssources[termv] = self._term_sources(termv)
        elif var in inserted:
            termv = var
            source = self._repo.locate_etype_source(inserted[var])
            termssources[termv] = set((source, solindex)
                                      for solindex in self._solindices)
        else:
            termv = self.rqlst.defined_vars[var.name]
            if not termv in termssources:
                termssources[termv] = self._term_sources(termv)
        return termv

    def _remove_sources_until_stable(self, term, termssources):
        sourcesterms = self._sourcesterms
        for oterm, rel in self._linkedterms.get(term, ()):
            tscope = ms_scope(term)
            otscope = ms_scope(oterm)
            rscope = ms_scope(rel)
            if not tscope is otscope and rscope.neged(strict=True):
                # can't get information from relation inside a NOT exists
                # where terms don't belong to the same scope
                continue
            need_ancestor_scope = False
            if not (tscope is rscope and otscope is rscope):
                if rel.ored():
                    continue
                if rel.ored(traverse_scope=True):
                    # if relation has some OR as parent, constraints should only
                    # propagate from parent scope to child scope, nothing else
                    need_ancestor_scope = True
            relsources = self._repo.rel_type_sources(rel.r_type)
            if neged_relation(rel) and (
                len(relsources) < 2
                or not isinstance(oterm, Variable)
                or oterm.valuable_references() != 1
                or any(sourcesterms[source][term] != sourcesterms[source][oterm]
                       for source in relsources
                       if term in sourcesterms.get(source, ())
                       and oterm in sourcesterms.get(source, ()))):
                # neged relation doesn't allow to infer term sources unless
                # we're on a multisource relation for a term only used by this
                # relation (eg "Any X WHERE NOT X multisource_rel Y" and over is
                # Y)
                continue
            # compute invalid sources for terms and remove them
            if not need_ancestor_scope or is_ancestor(tscope, otscope):
                self._remove_term_sources(term, rel, oterm, termssources)
            if not need_ancestor_scope or is_ancestor(otscope, tscope):
                self._remove_term_sources(oterm, rel, term, termssources)

    def _remove_term_sources(self, term, rel, oterm, termssources):
        """remove invalid sources for term according to oterm's sources and the
        relation between those two terms.
        """
        norelsup = self._norel_support_set(rel)
        termsources = termssources[term]
        invalid_sources = termsources - (termssources[oterm] | norelsup)
        if invalid_sources and self._repo.can_cross_relation(rel.r_type):
            invalid_sources -= self._sys_source_set
            if invalid_sources and isinstance(term, Variable) \
                   and self._need_ext_source_access(term, rel):
                # if the term is a not invariant variable, we should filter out
                # source where the relation is a cross relation from invalid
                # sources
                invalid_sources = frozenset((s, solidx) for s, solidx in invalid_sources
                                            if not (s in self._crossrelations and
                                                    rel in self._crossrelations[s]))
        if invalid_sources:
            self._remove_sources(term, invalid_sources)
            # if term is a rewritten const, we can apply the same changes to
            # all other consts inserted from the same original variable
            for const in self._const_vars.get(term, ()):
                if const is not term:
                    self._remove_sources(const, invalid_sources)
            termsources -= invalid_sources
            self._remove_sources_until_stable(term, termssources)
            if isinstance(oterm, Constant):
                self._remove_sources(oterm, invalid_sources)

    def _compute_needsplit(self):
        """tell according to sourcesterms if the rqlst has to be splitted for
        execution among multiple sources

        the execution has to be split if
        * a source support an entity (non invariant) but doesn't support a
          relation on it
        * a source support an entity which is accessed by an optional relation
        * there is more than one source and either all sources'supported
          variable/solutions are not equivalent or multiple variables have to
          be fetched from some source
        """
        # NOTE: < 2 since may be 0 on queries such as Any X WHERE X eid 2
        if len(self._sourcesterms) < 2:
            self.needsplit = False
            # if this is not the system source but we have only constant terms
            # and no relation (other than eid), apply query on the system source
            #
            # testing for rqlst with nothing in vargraph nor defined_vars is the
            # simplest way the check the condition explained below
            if not self.system_source in self._sourcesterms and \
                   not self.rqlst.defined_vars and \
                   not need_source_access_relation(self.rqlst.vargraph):
                self._sourcesterms = {self.system_source: {}}
        elif not self.needsplit:
            if not allequals(self._sourcesterms.itervalues()):
                for source, terms in self._sourcesterms.iteritems():
                    if source is self.system_source:
                        continue
                    if any(x for x in terms if not isinstance(x, Constant)):
                        self.needsplit = True
                        return
                self._sourcesterms = {self.system_source: {}}
                self.needsplit = False
            else:
                sample = self._sourcesterms.itervalues().next()
                if len(sample) > 1:
                    for term in sample:
                        # need split if unlinked variable
                        if isinstance(term, Variable) and not term in self._linkedterms:
                            self.needsplit = True
                            break
                    else:
                        # need split if there are some cross relation on non
                        # invariant variable or if the variable is used in
                        # multi-sources relation
                        if self._crossrelations:
                            for reldict in self._crossrelations.itervalues():
                                for rel, terms in reldict.iteritems():
                                    for term in terms:
                                        if isinstance(term, Variable) \
                                               and self._need_ext_source_access(term, rel):
                                            self.needsplit = True
                                            return

    @cached
    def _need_ext_source_access(self, var, rel):
        if not var._q_invariant:
            return True
        if  any(r for x, r in self._linkedterms[var]
                if not r is rel and self._repo.is_multi_sources_relation(r.r_type)):
            return True
        return False

    def _set_source_for_term(self, source, term):
        self._sourcesterms.setdefault(source, {})[term] = set(self._solindices)

    def _term_sources(self, term):
        """returns possible sources for terms `term`"""
        if isinstance(term, Constant):
            source = self._session.source_from_eid(term.eval(self.plan.args))
            return set((source, solindex) for solindex in self._solindices)
        else:
            var = getattr(term, 'variable', term)
            sources = [source for source, varobjs in self.sourcesterms.iteritems()
                       if var in varobjs]
            return set((source, solindex) for source in sources
                       for solindex in self.sourcesterms[source][var])

    def _remove_sources(self, term, sources):
        """removes invalid sources (`sources`) from `sourcesterms`

        :param sources: the list of sources to remove
        :param term: the analyzed term
        """
        sourcesterms = self._sourcesterms
        for source, solindex in sources:
            try:
                sourcesterms[source][term].remove(solindex)
            except KeyError:
                import rql.base as rqlb
                assert isinstance(term, (rqlb.BaseNode, Variable)), repr(term)
                continue # may occur with subquery column alias
            if not sourcesterms[source][term]:
                self._remove_source_term(source, term)

    def _remove_source_term(self, source, term, check=False):
        poped = self._sourcesterms[source].pop(term, None)
        if not self._sourcesterms[source]:
            del self._sourcesterms[source]
        if poped is not None and check:
            for terms in self._sourcesterms.itervalues():
                if term in terms:
                    break
            else:
                raise BadRQLQuery('source conflict for term %s' % term.as_string())

    def crossed_relation(self, source, relation):
        return relation in self._crossrelations.get(source, ())

    def part_steps(self):
        """precompute necessary part steps before generating actual rql for
        each step. This is necessary to know if an aggregate step will be
        necessary or not.
        """
        steps = []
        select = self.rqlst
        rschema = self._schema.rschema
        for source in self.part_sources:
            try:
                sourceterms = self._sourcesterms[source]
            except KeyError:
                continue # already proceed
            while sourceterms:
                # take a term randomly, and all terms supporting the
                # same solutions
                term, solindices = self._choose_term(sourceterms)
                if source.uri == 'system':
                    # ensure all variables are available for the latest step
                    # (missing one will be available from temporary tables
                    # of previous steps)
                    scope = select
                    terms = scope.defined_vars.values() + scope.aliases.values()
                    sourceterms.clear()
                    sources = [source]
                else:
                    scope = ms_scope(term)
                    # find which sources support the same term and solutions
                    sources = self._expand_sources(source, term, solindices)
                    # no try to get as much terms as possible
                    terms = self._expand_terms(term, sources, sourceterms,
                                               scope, solindices)
                    if len(terms) == 1 and isinstance(terms[0], Constant):
                        # we can't generate anything interesting with a single
                        # constant term (will generate an empty "Any" query),
                        # go to the next iteration directly!
                        continue
                    if not sourceterms:
                        try:
                            del self._sourcesterms[source]
                        except KeyError:
                            # XXX already cleaned
                            pass
                # set of terms which should be additionaly selected when
                # possible
                needsel = set()
                if not self._sourcesterms:
                    terms += scope.defined_vars.values() + scope.aliases.values()
                    final = True
                else:
                    # suppose this is a final step until the contrary is proven
                    final = scope is select
                    # add attribute variables and mark variables which should be
                    # additionaly selected when possible
                    for var in select.defined_vars.itervalues():
                        if not var in terms:
                            stinfo = var.stinfo
                            for ovar, rtype in stinfo.get('attrvars', ()):
                                if ovar in terms:
                                    needsel.add(var.name)
                                    terms.append(var)
                                    break
                            else:
                                needsel.add(var.name)
                                final = False
                    # check where all relations are supported by the sources
                    for rel in scope.iget_nodes(Relation):
                        if rel.is_types_restriction():
                            continue
                        # take care not overwriting the existing "source" identifier
                        for _source in sources:
                            if not _source.support_relation(rel.r_type) or (
                                self.crossed_relation(_source, rel) and not rel in terms):
                                for vref in rel.iget_nodes(VariableRef):
                                    needsel.add(vref.name)
                                final = False
                                break
                        else:
                            if not scope is select:
                                self._exists_relation(rel, terms, needsel)
                            # if relation is supported by all sources and some of
                            # its lhs/rhs variable isn't in "terms", and the
                            # other end *is* in "terms", mark it have to be
                            # selected
                            if source.uri != 'system' and not rschema(rel.r_type).final:
                                lhs, rhs = rel.get_variable_parts()
                                try:
                                    lhsvar = lhs.variable
                                except AttributeError:
                                    lhsvar = lhs
                                try:
                                    rhsvar = rhs.variable
                                except AttributeError:
                                    rhsvar = rhs
                                try:
                                    if lhsvar in terms and not rhsvar in terms:
                                        needsel.add(lhsvar.name)
                                    elif rhsvar in terms and not lhsvar in terms:
                                        needsel.add(rhsvar.name)
                                except AttributeError:
                                    continue # not an attribute, no selection needed
                if final and source.uri != 'system':
                    # check rewritten constants
                    for vconsts in select.stinfo['rewritten'].itervalues():
                        const = vconsts[0]
                        eid = const.eval(self.plan.args)
                        _source = self._session.source_from_eid(eid)
                        if len(sources) > 1 or not _source in sources:
                            # if there is some rewriten constant used by a not
                            # neged relation while there are some source not
                            # supporting the associated entity, this step can't
                            # be final (unless the relation is explicitly in
                            # `terms`, eg cross relations)
                            for c in vconsts:
                                rel = c.relation()
                                if rel is None or not (rel in terms or neged_relation(rel)):
                                    final = False
                                    break
                            break
                if final:
                    self._cleanup_sourcesterms(sources, solindices)
                steps.append((sources, terms, solindices, scope, needsel, final)
                             )
        return steps

    def _exists_relation(self, rel, terms, needsel):
        rschema = self._schema.rschema(rel.r_type)
        lhs, rhs = rel.get_variable_parts()
        try:
            lhsvar, rhsvar = lhs.variable, rhs.variable
        except AttributeError:
            pass
        else:
            # supported relation with at least one end supported, check the
            # other end is in as well. If not this usually means the
            # variable is refed by an outer scope and should be substituted
            # using an 'identity' relation (else we'll get a conflict of
            # temporary tables)
            if rhsvar in terms and not lhsvar in terms and ms_scope(lhsvar) is lhsvar.stmt:
                self._identity_substitute(rel, lhsvar, terms, needsel)
            elif lhsvar in terms and not rhsvar in terms and ms_scope(rhsvar) is rhsvar.stmt:
                self._identity_substitute(rel, rhsvar, terms, needsel)

    def _identity_substitute(self, relation, var, terms, needsel):
        newvar = self._insert_identity_variable(ms_scope(relation), var)
        # ensure relation is using '=' operator, else we rely on a
        # sqlgenerator side effect (it won't insert an inequality operator
        # in this case)
        relation.children[1].operator = '='
        terms.append(newvar)
        needsel.add(newvar.name)

    def _choose_term(self, sourceterms):
        """pick one term among terms supported by a source, which will be used
        as a base to generate an execution step
        """
        secondchoice = None
        if len(self._sourcesterms) > 1:
            # priority to variable from subscopes
            for term in sourceterms:
                if not ms_scope(term) is self.rqlst:
                    if isinstance(term, Variable):
                        return term, sourceterms.pop(term)
                    secondchoice = term
        else:
            # priority to variable from outer scope
            for term in sourceterms:
                if ms_scope(term) is self.rqlst:
                    if isinstance(term, Variable):
                        return term, sourceterms.pop(term)
                    secondchoice = term
        if secondchoice is not None:
            return secondchoice, sourceterms.pop(secondchoice)
        # priority to variable with the less solutions supported and with the
        # most valuable refs. Add variable name for test predictability
        variables = sorted([(var, sols) for (var, sols) in sourceterms.items()
                            if isinstance(var, Variable)],
                           key=lambda (v, s): (len(s), -v.valuable_references(), v.name))
        if variables:
            var = variables[0][0]
            return var, sourceterms.pop(var)
        # priority to constant
        for term in sourceterms:
            if isinstance(term, Constant):
                return term, sourceterms.pop(term)
        # whatever (relation)
        term = iter(sourceterms).next()
        return term, sourceterms.pop(term)

    def _expand_sources(self, selected_source, term, solindices):
        """return all sources supporting given term / solindices"""
        sources = [selected_source]
        sourcesterms = self._sourcesterms
        for source in sourcesterms.keys():
            if source is selected_source:
                continue
            if not (term in sourcesterms[source] and
                    solindices.issubset(sourcesterms[source][term])):
                continue
            sources.append(source)
            if source.uri != 'system' or not (isinstance(term, Variable) and not term in self._linkedterms):
                termsolindices = sourcesterms[source][term]
                termsolindices -= solindices
                if not termsolindices:
                    del sourcesterms[source][term]
                    if not sourcesterms[source]:
                        del sourcesterms[source]
        return sources

    def _expand_terms(self, term, sources, sourceterms, scope, solindices):
        terms = [term]
        sources = sorted(sources)
        sourcesterms = self._sourcesterms
        linkedterms = self._linkedterms
        # term has to belong to the same scope if there is more
        # than the system source remaining
        if len(sourcesterms) > 1 and not scope is self.rqlst:
            candidates = (t for t in sourceterms.keys() if scope is ms_scope(t))
        else:
            candidates = sourceterms #.iterkeys()
        # we only want one unlinked term in each generated query
        candidates = [t for t in candidates
                      if isinstance(t, (Constant, Relation)) or
                      (solindices.issubset(sourceterms[t]) and t in linkedterms)]
        cross_rels = {}
        for source in sources:
            cross_rels.update(self._crossrelations.get(source, {}))
        exclude = {}
        for crossvars in cross_rels.itervalues():
            vars = [t for t in crossvars if isinstance(t, Variable)]
            try:
                exclude[vars[0]] = vars[1]
                exclude[vars[1]] = vars[0]
            except IndexError:
                pass
        accept_term = lambda x: (not any(s for s in sources
                                         if not x in sourcesterms.get(s, ()))
                                 and x._ms_may_be_processed(terms, linkedterms)
                                 and not exclude.get(x) in terms)
        if isinstance(term, Relation) and term in cross_rels:
            cross_terms = cross_rels.pop(term)
            base_accept_term = accept_term
            accept_term = lambda x: (accept_term(x) or x in cross_terms)
            for refed in cross_terms:
                if not refed in candidates:
                    terms.append(refed)
        # repeat until no term can't be added, since addition of a new
        # term may permit to another one to be added
        modified = True
        while modified and candidates:
            modified = False
            for term in candidates[:]:
                if isinstance(term, Constant):
                    termsources = set(x[0] for x in self._term_sources(term))
                    # ensure system source is there for constant
                    if self.system_source in sources:
                        termsources.add(self.system_source)
                    if sorted(termsources) != sources:
                        continue
                    terms.append(term)
                    candidates.remove(term)
                    modified = True
                    del sourceterms[term]
                elif accept_term(term):
                    terms.append(term)
                    candidates.remove(term)
                    modified = True
                    self._cleanup_sourcesterms(sources, solindices, term)
        return terms

    def _cleanup_sourcesterms(self, sources, solindices, term=None):
        """remove solutions so we know they are already processed"""
        for source in sources:
            try:
                sourceterms = self._sourcesterms[source]
            except KeyError:
                continue
            if term is None:
                for term, termsolindices in sourceterms.items():
                    if isinstance(term, Relation) and self.crossed_relation(source, term):
                        continue
                    termsolindices -= solindices
                    if not termsolindices:
                        del sourceterms[term]
            else:
                try:
                    sourceterms[term] -= solindices
                    if not sourceterms[term]:
                        del sourceterms[term]
                except KeyError:
                    pass
                    #assert term in cross_terms
            if not sourceterms:
                del self._sourcesterms[source]

    def merge_input_maps(self, allsolindices):
        """inputmaps is a dictionary with tuple of solution indices as key with
        an associated input map as value. This function compute for each
        solution its necessary input map and return them grouped

        ex:
        inputmaps = {(0, 1, 2): {'A': 't1.login1', 'U': 't1.C0', 'U.login': 't1.login1'},
                     (1,): {'X': 't2.C0', 'T': 't2.C1'}}
        return : [([1],  {'A': 't1.login1', 'U': 't1.C0', 'U.login': 't1.login1',
                           'X': 't2.C0', 'T': 't2.C1'}),
                  ([0,2], {'A': 't1.login1', 'U': 't1.C0', 'U.login': 't1.login1'})]
        """
        if not self._inputmaps:
            return [(allsolindices, None)]
        mapbysol = {}
        # compute a single map for each solution
        for solindices, basemap in self._inputmaps.iteritems():
            for solindex in solindices:
                solmap = mapbysol.setdefault(solindex, {})
                solmap.update(basemap)
                try:
                    allsolindices.remove(solindex)
                except KeyError:
                    continue # already removed
        # group results by identical input map
        result = []
        for solindex, solmap in mapbysol.iteritems():
            for solindices, commonmap in result:
                if commonmap == solmap:
                    solindices.append(solindex)
                    break
            else:
                result.append( ([solindex], solmap) )
        if allsolindices:
            result.append( (list(allsolindices), None) )
        return result

    def build_final_part(self, select, solindices, inputmap,  sources,
                         insertedvars):
        solutions = [self._solutions[i] for i in solindices]
        if self._conflicts:
            for varname, mappedto in self._conflicts:
                var = select.defined_vars[varname]
                newvar = select.make_variable()
                # XXX should use var.scope but scope hasn't been computed yet
                select.add_relation(var, 'identity', newvar)
                for sol in solutions:
                    sol[newvar.name] = sol[varname]
                inputmap[newvar.name] = mappedto
        rqlst = self.plan.finalize(select, solutions, insertedvars)
        if self.temptable is None and self.finaltable is None:
            return OneFetchStep(self.plan, rqlst, sources, inputmap=inputmap)
        table = self.temptable or self.finaltable
        return FetchStep(self.plan, rqlst, sources, table, True, inputmap)

    def build_non_final_part(self, select, solindices, sources, insertedvars,
                             table):
        """non final step, will have to store results in a temporary table"""
        solutions = [self._solutions[i] for i in solindices]
        rqlst = self.plan.finalize(select, solutions, insertedvars)
        step = FetchStep(self.plan, rqlst, sources, table, False)
        # update input map for following steps, according to processed solutions
        inputmapkey = tuple(sorted(solindices))
        inputmap = self._inputmaps.setdefault(inputmapkey, {})
        for varname, mapping in step.outputmap.iteritems():
            if varname in inputmap and \
                   not (mapping == inputmap[varname] or
                        self._schema.eschema(solutions[0][varname]).final):
                self._conflicts.append((varname, inputmap[varname]))
        inputmap.update(step.outputmap)
        self.plan.add_step(step)


class MSPlanner(SSPlanner):
    """MultiSourcesPlanner: build execution plan for rql queries

    decompose the RQL query according to sources'schema
    """

    def build_select_plan(self, plan, rqlst):
        """build execution plan for a SELECT RQL query

        the rqlst should not be tagged at this point
        """
        # preprocess deals with security insertion and returns a new syntax tree
        # which have to be executed to fulfill the query: according
        # to permissions for variable's type, different rql queries may have to
        # be executed
        plan.preprocess(rqlst)
        if server.DEBUG & server.DBG_MS:
            print '-'*80
            print 'PLANNING', rqlst
        ppis = [PartPlanInformation(plan, select, self.rqlhelper)
                for select in rqlst.children]
        steps = self._union_plan(plan, ppis)
        if server.DEBUG & server.DBG_MS:
            from pprint import pprint
            for step in plan.steps:
                pprint(step.test_repr())
            pprint(steps[0].test_repr())
        return steps

    def _ppi_subqueries(self, ppi):
        # part plan info for subqueries
        plan = ppi.plan
        inputmap = {}
        for subquery in ppi.rqlst.with_[:]:
            sppis = [PartPlanInformation(plan, select)
                     for select in subquery.query.children]
            for sppi in sppis:
                if sppi.needsplit or sppi.part_sources != ppi.part_sources:
                    temptable = plan.make_temp_table_name('T%s' % make_uid(id(subquery)))
                    sstep = self._union_plan(plan, sppis, temptable)[0]
                    break
            else:
                sstep = None
            if sstep is not None:
                ppi.rqlst.with_.remove(subquery)
                for i, colalias in enumerate(subquery.aliases):
                    inputmap[colalias.name] = '%s.C%s' % (temptable, i)
                ppi.plan.add_step(sstep)
        return inputmap

    def _union_plan(self, plan, ppis, temptable=None):
        tosplit, cango, allsources = [], {}, set()
        for planinfo in ppis:
            if planinfo.needsplit:
                tosplit.append(planinfo)
            else:
                cango.setdefault(planinfo.part_sources, []).append(planinfo)
            for source in planinfo.part_sources:
                allsources.add(source)
        # first add steps for query parts which doesn't need to splitted
        steps = []
        for sources, cppis in cango.iteritems():
            byinputmap = {}
            for ppi in cppis:
                select = ppi.rqlst
                if sources != (ppi.system_source,):
                    add_types_restriction(self.schema, select)
                # part plan info for subqueries
                inputmap = self._ppi_subqueries(ppi)
                aggrstep = need_aggr_step(select, sources)
                if aggrstep:
                    atemptable = plan.make_temp_table_name('T%s' % make_uid(id(select)))
                    sunion = Union()
                    sunion.append(select)
                    selected = select.selection[:]
                    select_group_sort(select)
                    step = AggrStep(plan, selected, select, atemptable, temptable)
                    step.set_limit_offset(select.limit, select.offset)
                    select.limit = None
                    select.offset = 0
                    fstep = FetchStep(plan, sunion, sources, atemptable, True, inputmap)
                    step.children.append(fstep)
                    steps.append(step)
                else:
                    byinputmap.setdefault(tuple(inputmap.iteritems()), []).append( (select) )
            for inputmap, queries in byinputmap.iteritems():
                inputmap = dict(inputmap)
                sunion = Union()
                for select in queries:
                    sunion.append(select)
                if temptable:
                    steps.append(FetchStep(plan, sunion, sources, temptable, True, inputmap))
                else:
                    steps.append(OneFetchStep(plan, sunion, sources, inputmap))
        # then add steps for splitted query parts
        for planinfo in tosplit:
            steps.append(self.split_part(planinfo, temptable))
        if len(steps) > 1:
            if temptable:
                step = UnionFetchStep(plan)
            else:
                step = UnionStep(plan)
            step.children = steps
            return (step,)
        return steps

    # internal methods for multisources decomposition #########################

    def split_part(self, ppi, temptable):
        ppi.finaltable = temptable
        plan = ppi.plan
        select = ppi.rqlst
        subinputmap = self._ppi_subqueries(ppi)
        stepdefs = ppi.part_steps()
        if need_aggr_step(select, ppi.part_sources, stepdefs):
            atemptable = plan.make_temp_table_name('T%s' % make_uid(id(select)))
            selection = select.selection[:]
            select_group_sort(select)
        else:
            atemptable = None
            selection = select.selection
        ppi.temptable = atemptable
        vfilter = TermsFiltererVisitor(self.schema, ppi)
        steps = []
        for sources, terms, solindices, scope, needsel, final in stepdefs:
            # extract an executable query using only the specified terms
            if sources[0].uri == 'system':
                # in this case we have to merge input maps before call to
                # filter so already processed restriction are correctly
                # removed
                solsinputmaps = ppi.merge_input_maps(solindices)
                for solindices, inputmap in solsinputmaps:
                    minrqlst, insertedvars = vfilter.filter(
                        sources, terms, scope, set(solindices), needsel, final)
                    if inputmap is None:
                        inputmap = subinputmap
                    else:
                        inputmap.update(subinputmap)
                    steps.append(ppi.build_final_part(minrqlst, solindices, inputmap,
                                                      sources, insertedvars))
            else:
                # this is a final part (i.e. retreiving results for the
                # original query part) if all term / sources have been
                # treated or if this is the last shot for used solutions
                minrqlst, insertedvars = vfilter.filter(
                    sources, terms, scope, solindices, needsel, final)
                if final:
                    solsinputmaps = ppi.merge_input_maps(solindices)
                    if len(solsinputmaps) > 1:
                        refrqlst = minrqlst
                    for solindices, inputmap in solsinputmaps:
                        if inputmap is None:
                            inputmap = subinputmap
                        else:
                            inputmap.update(subinputmap)
                        if len(solsinputmaps) > 1:
                            minrqlst = refrqlst.copy()
                            sources = sources[:]
                        if inputmap and len(sources) > 1:
                            sources.remove(ppi.system_source)
                            steps.append(ppi.build_final_part(minrqlst, solindices, None,
                                                              sources, insertedvars))
                            steps.append(ppi.build_final_part(minrqlst, solindices, inputmap,
                                                              [ppi.system_source], insertedvars))
                        else:
                            steps.append(ppi.build_final_part(minrqlst, solindices, inputmap,
                                                              sources, insertedvars))
                else:
                    table = '_T%s%s' % (''.join(sorted(v._ms_table_key() for v in terms)),
                                        ''.join(sorted(str(i) for i in solindices)))
                    table = plan.make_temp_table_name(table)
                    ppi.build_non_final_part(minrqlst, solindices, sources,
                                             insertedvars, table)
        # finally: join parts, deal with aggregat/group/sorts if necessary
        if atemptable is not None:
            step = AggrStep(plan, selection, select, atemptable, temptable)
            step.children = steps
        elif len(steps) > 1:
            getrschema = self.schema.rschema
            if need_intersect(select, getrschema) or any(need_intersect(select, getrschema)
                                                         for step in steps
                                                         for select in step.union.children):
                if temptable:
                    step = IntersectFetchStep(plan) # XXX not implemented
                else:
                    step = IntersectStep(plan)
            else:
                if temptable:
                    step = UnionFetchStep(plan)
                else:
                    step = UnionStep(plan)
            step.children = steps
        else:
            step = steps[0]
        if select.limit is not None or select.offset:
            step.set_limit_offset(select.limit, select.offset)
        return step


class UnsupportedBranch(Exception):
    pass


class TermsFiltererVisitor(object):
    def __init__(self, schema, ppi):
        self.schema = schema
        self.ppi = ppi
        self.skip = {}
        self.hasaggrstep = self.ppi.temptable
        self.extneedsel = frozenset(vref.name for sortterm in ppi.rqlst.orderby
                                    for vref in sortterm.iget_nodes(VariableRef))

    def _rqlst_accept(self, rqlst, node, newroot, terms, setfunc=None):
        try:
            newrestr, node_ = node.accept(self, newroot, terms[:])
        except UnsupportedBranch:
            return rqlst
        if setfunc is not None and newrestr is not None:
            setfunc(newrestr)
        if not node_ is node:
            rqlst = node.parent
        return rqlst

    def filter(self, sources, terms, rqlst, solindices, needsel, final):
        if server.DEBUG & server.DBG_MS:
            print 'filter', final and 'final' or '', sources, terms, rqlst, solindices, needsel
        newroot = Select()
        self.sources = sorted(sources)
        self.terms = terms
        self.solindices = solindices
        self.final = final
        self._pending_vrefs = []
        # terms which appear in unsupported branches
        needsel |= self.extneedsel
        self.needsel = needsel
        # terms which appear in supported branches
        self.mayneedsel = set()
        # new inserted variables
        self.insertedvars = []
        # other structures (XXX document)
        self.mayneedvar, self.hasvar = {}, {}
        self.use_only_defined = False
        self.scopes = {rqlst: newroot}
        self.current_scope = rqlst
        if rqlst.where:
            rqlst = self._rqlst_accept(rqlst, rqlst.where, newroot, terms,
                                       newroot.set_where)
        if isinstance(rqlst, Select):
            self.use_only_defined = True
            if rqlst.groupby:
                groupby = []
                for node in rqlst.groupby:
                    rqlst = self._rqlst_accept(rqlst, node, newroot, terms,
                                               groupby.append)
                if groupby:
                    newroot.set_groupby(groupby)
            if rqlst.having:
                having = []
                for node in rqlst.having:
                    rqlst = self._rqlst_accept(rqlst, node, newroot, terms,
                                               having.append)
                if having:
                    newroot.set_having(having)
            if final and rqlst.orderby and not self.hasaggrstep:
                orderby = []
                for node in rqlst.orderby:
                    rqlst = self._rqlst_accept(rqlst, node, newroot, terms,
                                               orderby.append)
                if orderby:
                    newroot.set_orderby(orderby)
            elif rqlst.orderby:
                for sortterm in rqlst.orderby:
                    if any(f for f in sortterm.iget_nodes(Function) if f.name == 'FTIRANK'):
                        newnode, oldnode = sortterm.accept(self, newroot, terms)
                        if newnode is not None:
                            newroot.add_sort_term(newnode)
            self.process_selection(newroot, terms, rqlst)
        elif not newroot.where:
            # no restrictions have been copied, just select terms and add
            # type restriction (done later by add_types_restriction)
            for v in terms:
                if not isinstance(v, Variable):
                    continue
                newroot.append_selected(VariableRef(newroot.get_variable(v.name)))
        solutions = self.ppi.copy_solutions(solindices)
        cleanup_solutions(newroot, solutions)
        newroot.set_possible_types(solutions)
        if final:
            if self.hasaggrstep:
                self.add_necessary_selection(newroot, self.mayneedsel & self.extneedsel)
            newroot.distinct = rqlst.distinct
        else:
            self.add_necessary_selection(newroot, self.mayneedsel & self.needsel)
            # insert vars to fetch constant values when needed
            for (varname, rschema), reldefs in self.mayneedvar.iteritems():
                for rel, ored in reldefs:
                    if not (varname, rschema) in self.hasvar:
                        self.hasvar[(varname, rschema)] = None # just to avoid further insertion
                        cvar = newroot.make_variable()
                        for sol in newroot.solutions:
                            sol[cvar.name] = rschema.objects(sol[varname])[0]
                        # if the current restriction is not used in a OR branch,
                        # we can keep it, else we have to drop the constant
                        # restriction (or we may miss some results)
                        if not ored:
                            rel = rel.copy(newroot)
                            newroot.add_restriction(rel)
                        # add a relation to link the variable
                        newroot.remove_node(rel.children[1])
                        cmp = Comparison('=')
                        rel.append(cmp)
                        cmp.append(VariableRef(cvar))
                        self.insertedvars.append((varname, rschema, cvar.name))
                        newroot.append_selected(VariableRef(newroot.get_variable(cvar.name)))
                        # NOTE: even if the restriction is done by this query, we have
                        # to let it in the original rqlst so that it appears anyway in
                        # the "final" query, else we may change the meaning of the query
                        # if there are NOT somewhere :
                        # 'NOT X relation Y, Y name "toto"' means X WHERE X isn't related
                        # to Y whose name is toto while
                        # 'NOT X relation Y' means X WHERE X has no 'relation' (whatever Y)
                    elif ored:
                        newroot.remove_node(rel)
        add_types_restriction(self.schema, rqlst, newroot, solutions)
        if server.DEBUG & server.DBG_MS:
            print '--->', newroot
        return newroot, self.insertedvars

    def visit_and(self, node, newroot, terms):
        subparts = []
        for i in xrange(len(node.children)):
            child = node.children[i]
            try:
                newchild, child_ = child.accept(self, newroot, terms)
                if not child_ is child:
                    node = child_.parent
                if newchild is None:
                    continue
                subparts.append(newchild)
            except UnsupportedBranch:
                continue
        if not subparts:
            return None, node
        if len(subparts) == 1:
            return subparts[0], node
        return copy_node(newroot, node, subparts), node

    visit_or = visit_and

    def _relation_supported(self, relation):
        rtype = relation.r_type
        for source in self.sources:
            if not source.support_relation(rtype) or (
                rtype in source.cross_relations and not relation in self.terms):
                return False
        if not self.final and not relation in self.terms:
            rschema = self.schema.rschema(relation.r_type)
            if not rschema.final:
                for term in relation.get_nodes((VariableRef, Constant)):
                    term = getattr(term, 'variable', term)
                    termsources = sorted(set(x[0] for x in self.ppi._term_sources(term)))
                    if termsources and termsources != self.sources:
                        return False
        return True

    def visit_relation(self, node, newroot, terms):
        if not node.is_types_restriction():
            if node in self.skip and self.solindices.issubset(self.skip[node]):
                if not self.schema.rschema(node.r_type).final:
                    # can't really skip the relation if one variable is selected
                    # and only referenced by this relation
                    for vref in node.iget_nodes(VariableRef):
                        stinfo = vref.variable.stinfo
                        if stinfo['selected'] and len(stinfo['relations']) == 1:
                            break
                    else:
                        return None, node
                else:
                    return None, node
            if not self._relation_supported(node):
                raise UnsupportedBranch()
        # don't copy type restriction unless this is the only supported relation
        # for the lhs variable, else they'll be reinserted later as needed (in
        # other cases we may copy a type restriction while the variable is not
        # actually used)
        elif not (node.neged(strict=True) or
                  any(self._relation_supported(rel)
                      for rel in node.children[0].variable.stinfo['relations'])):
            return self.visit_default(node, newroot, terms)
        else:
            raise UnsupportedBranch()
        rschema = self.schema.rschema(node.r_type)
        self._pending_vrefs = []
        try:
            res = self.visit_default(node, newroot, terms)[0]
        except:
            # when a relation isn't supported, we should dereference potentially
            # introduced variable refs
            for vref in self._pending_vrefs:
                vref.unregister_reference()
            raise
        ored = node.ored()
        if rschema.final or rschema.inlined:
            vrefs = node.children[1].get_nodes(VariableRef)
            if not vrefs:
                if not ored:
                    self.skip.setdefault(node, set()).update(self.solindices)
                else:
                    self.mayneedvar.setdefault((node.children[0].name, rschema), []).append( (res, ored) )
            else:
                assert len(vrefs) == 1
                vref = vrefs[0]
                # XXX check operator ?
                self.hasvar[(node.children[0].name, rschema)] = vref
                if self._may_skip_attr_rel(rschema, node, vref, ored, terms, res):
                    self.skip.setdefault(node, set()).update(self.solindices)
        elif not ored:
            self.skip.setdefault(node, set()).update(self.solindices)
        return res, node

    def _may_skip_attr_rel(self, rschema, rel, vref, ored, terms, res):
        var = vref.variable
        if ored:
            return False
        if var.name in self.extneedsel or var.stinfo['selected']:
            return False
        if not var in terms or used_in_outer_scope(var, self.current_scope):
            return False
        if any(v for v, _ in var.stinfo.get('attrvars', ()) if not v in terms):
            return False
        return True

    def visit_exists(self, node, newroot, terms):
        newexists = node.__class__()
        self.scopes = {node: newexists}
        subparts, node = self._visit_children(node, newroot, terms)
        if not subparts:
            return None, node
        newexists.set_where(subparts[0])
        return newexists, node

    def visit_not(self, node, newroot, terms):
        subparts, node = self._visit_children(node, newroot, terms)
        if not subparts:
            return None, node
        return copy_node(newroot, node, subparts), node

    def visit_group(self, node, newroot, terms):
        if not self.final:
            return None, node
        return self.visit_default(node, newroot, terms)

    def visit_variableref(self, node, newroot, terms):
        if self.use_only_defined:
            if not node.variable.name in newroot.defined_vars:
                raise UnsupportedBranch(node.name)
        elif not node.variable in terms:
            raise UnsupportedBranch(node.name)
        self.mayneedsel.add(node.name)
        # set scope so we can insert types restriction properly
        newvar = newroot.get_variable(node.name)
        newvar.stinfo['scope'] = self.scopes.get(node.variable.scope, newroot)
        vref = VariableRef(newvar)
        self._pending_vrefs.append(vref)
        return vref, node

    def visit_constant(self, node, newroot, terms):
        return copy_node(newroot, node), node

    def visit_comparison(self, node, newroot, terms):
        subparts, node = self._visit_children(node, newroot, terms)
        copy = copy_node(newroot, node, subparts)
        # ignore comparison operator when fetching non final query
        if not self.final and isinstance(node.children[0], VariableRef):
            copy.operator = '='
        return copy, node

    def visit_function(self, node, newroot, terms):
        if node.name == 'FTIRANK':
            # FTIRANK is somewhat special... Rank function should be included in
            # the same query has the has_text relation, potentially added to
            # selection for latter usage
            if not self.hasaggrstep and self.final and node not in self.skip:
                return self.visit_default(node, newroot, terms)
            elif any(s for s in self.sources if s.uri != 'system'):
                return None, node
            # p = node.parent
            # while p is not None and not isinstance(p, SortTerm):
            #     p = p.parent
            # if isinstance(p, SortTerm):
            if not self.hasaggrstep and self.final and node in self.skip:
                return Constant(self.skip[node], 'Int'), node
            # XXX only if not yet selected
            newroot.append_selected(node.copy(newroot))
            self.skip[node] = len(newroot.selection)
            return None, node
        return self.visit_default(node, newroot, terms)

    def visit_default(self, node, newroot, terms):
        subparts, node = self._visit_children(node, newroot, terms)
        return copy_node(newroot, node, subparts), node

    visit_mathexpression = visit_constant = visit_default

    def visit_sortterm(self, node, newroot, terms):
        subparts, node = self._visit_children(node, newroot, terms)
        if not subparts:
            return None, node
        return copy_node(newroot, node, subparts), node

    def _visit_children(self, node, newroot, terms):
        subparts = []
        for i in xrange(len(node.children)):
            child = node.children[i]
            newchild, child_ = child.accept(self, newroot, terms)
            if not child is child_:
                node = child_.parent
            if newchild is not None:
                subparts.append(newchild)
        return subparts, node

    def process_selection(self, newroot, terms, rqlst):
        if self.final:
            for term in rqlst.selection:
                newroot.append_selected(term.copy(newroot))
                for vref in term.get_nodes(VariableRef):
                    self.needsel.add(vref.name)
            return
        for term in rqlst.selection:
            vrefs = term.get_nodes(VariableRef)
            if vrefs:
                supportedvars = []
                for vref in vrefs:
                    var = vref.variable
                    if var in terms:
                        supportedvars.append(vref)
                        continue
                    else:
                        self.needsel.add(vref.name)
                        break
                else:
                    for vref in vrefs:
                        newroot.append_selected(vref.copy(newroot))
                    supportedvars = []
                for vref in supportedvars:
                    if not vref in newroot.get_selected_variables():
                        newroot.append_selected(VariableRef(newroot.get_variable(vref.name)))
            elif term in self.terms:
                newroot.append_selected(term.copy(newroot))

    def add_necessary_selection(self, newroot, terms):
        selected = tuple(newroot.get_selected_variables())
        for varname in terms:
            var = newroot.defined_vars[varname]
            for vref in var.references():
                rel = vref.relation()
                if rel is None and vref in selected:
                    # already selected
                    break
            else:
                selvref = VariableRef(var)
                newroot.append_selected(selvref)
                if newroot.groupby:
                    newroot.add_group_var(VariableRef(selvref.variable, noautoref=1))
