"""RQL rewriting utilities : insert rql expression snippets into rql syntax

tree.

This is used for instance for read security checking in the repository.

:organization: Logilab

:copyright: 2007-2009 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

"""

__docformat__ = "restructuredtext en"

from rql import nodes as n, stmts, TypeResolverException

from logilab.common.compat import any

from cubicweb import Unauthorized, server, typed_eid

from cubicweb.server.ssplanner import add_types_restriction

def remove_solutions(origsolutions, solutions, defined):

    """when a rqlst has been generated from another by introducing security

    assertions, this method returns solutions which are contained in orig

    solutions

    """

    newsolutions = []

    for origsol in origsolutions:

        for newsol in solutions[:]:

            for var, etype in origsol.items():

                try:

                    if newsol[var] != etype:

                        try:

                            defined[var].stinfo['possibletypes'].remove(newsol[var])

                        except KeyError:

                            pass

                        break

                except KeyError:

                    # variable has been rewritten

                    continue

            else:

                newsolutions.append(newsol)

                solutions.remove(newsol)

    return newsolutions

class Unsupported(Exception): pass

class RQLRewriter(object):

    """insert some rql snippets into another rql syntax tree

    this class *isn't thread safe*

    """

    def __init__(self, session):

        self.session = session

        vreg = session.vreg

        self.schema = vreg.schema

        self.annotate = vreg.rqlhelper.annotate

        self._compute_solutions = vreg.solutions

    def compute_solutions(self):

        self.annotate(self.select)

        try:

            self._compute_solutions(self.session, self.select, self.kwargs)

        except TypeResolverException:

            raise Unsupported(str(self.select))

        if len(self.select.solutions) < len(self.solutions):

            raise Unsupported()

    def rewrite(self, select, snippets, solutions, kwargs):

        """

        snippets: (varmap, list of rql expression)

                  with varmap a *tuple* (select var, snippet var)

        """

        if server.DEBUG:

            print '---- rewrite', select, snippets, solutions

        self.select = self.insert_scope = select

        self.solutions = solutions

        self.kwargs = kwargs

        self.u_varname = None

        self.removing_ambiguity = False

        self.exists_snippet = {}

        self.pending_keys = []

        # we have to annotate the rqlst before inserting snippets, even though

        # we'll have to redo it latter

        self.annotate(select)

        self.insert_snippets(snippets)

        if not self.exists_snippet and self.u_varname:

            # U has been inserted than cancelled, cleanup

            select.undefine_variable(select.defined_vars[self.u_varname])

        # clean solutions according to initial solutions

        newsolutions = remove_solutions(solutions, select.solutions,

                                        select.defined_vars)

        assert len(newsolutions) >= len(solutions), (

            'rewritten rql %s has lost some solutions, there is probably '

            'something wrong in your schema permission (for instance using a '

            'RQLExpression which insert a relation which doesn\'t exists in '

            'the schema)\nOrig solutions: %s\nnew solutions: %s' % (

            select, solutions, newsolutions))

        if len(newsolutions) > len(solutions):

            newsolutions = self.remove_ambiguities(snippets, newsolutions)

        select.solutions = newsolutions

        add_types_restriction(self.schema, select)

        if server.DEBUG:

            print '---- rewriten', select

    def insert_snippets(self, snippets, varexistsmap=None):

        self.rewritten = {}

        for varmap, rqlexprs in snippets:

            if varexistsmap is not None and not varmap in varexistsmap:

                continue

            self.varmap = varmap

            selectvar, snippetvar = varmap

            assert snippetvar in 'SOX'

            self.revvarmap = {snippetvar: selectvar}

            self.varinfo = vi = {}

            try:

                vi['const'] = typed_eid(selectvar) # XXX gae

                vi['rhs_rels'] = vi['lhs_rels'] = {}

            except ValueError:

                vi['stinfo'] = sti = self.select.defined_vars[selectvar].stinfo

                if varexistsmap is None:

                    vi['rhs_rels'] = dict( (r.r_type, r) for r in sti['rhsrelations'])

                    vi['lhs_rels'] = dict( (r.r_type, r) for r in sti['relations']

                                           if not r in sti['rhsrelations'])

                else:

                    vi['rhs_rels'] = vi['lhs_rels'] = {}

            parent = None

            inserted = False

            for rqlexpr in rqlexprs:

                self.current_expr = rqlexpr

                if varexistsmap is None:

                    try:

                        new = self.insert_snippet(varmap, rqlexpr.snippet_rqlst, parent)

                    except Unsupported:

                        import traceback

                        traceback.print_exc()

                        continue

                    inserted = True

                    if new is not None:

                        self.exists_snippet[rqlexpr] = new

                    parent = parent or new

                else:

                    # called to reintroduce snippet due to ambiguity creation,

                    # so skip snippets which are not introducing this ambiguity

                    exists = varexistsmap[varmap]

                    if self.exists_snippet[rqlexpr] is exists:

                        self.insert_snippet(varmap, rqlexpr.snippet_rqlst, exists)

            if varexistsmap is None and not inserted:

                # no rql expression found matching rql solutions. User has no access right

                raise Unauthorized()

    def insert_snippet(self, varmap, snippetrqlst, parent=None):

        new = snippetrqlst.where.accept(self)

        if new is not None:

            if self.varinfo.get('stinfo', {}).get('optrelations'):

                assert parent is None

                self.insert_scope = self.snippet_subquery(varmap, new)

                self.insert_pending()

                self.insert_scope = self.select

                return

            new = n.Exists(new)

            if parent is None:

                self.insert_scope.add_restriction(new)

            else:

                grandpa = parent.parent

                or_ = n.Or(parent, new)

                grandpa.replace(parent, or_)

            if not self.removing_ambiguity:

                try:

                    self.compute_solutions()

                except Unsupported:

                    # some solutions have been lost, can't apply this rql expr

                    if parent is None:

                        self.select.remove_node(new, undefine=True)

                    else:

                        parent.parent.replace(or_, or_.children[0])

                        self._cleanup_inserted(new)

                    raise

                else:

                    self.insert_scope = new

                    self.insert_pending()

                    self.insert_scope = self.select

            return new

        self.insert_pending()

    def insert_pending(self):

        """pending_keys hold variable referenced by U has_<action>_permission X

        relation.

        Once the snippet introducing this has been inserted and solutions

        recomputed, we have to insert snippet defined for <action> of entity

        types taken by X

        """

        while self.pending_keys:

            key, action = self.pending_keys.pop()

            try:

                varname = self.rewritten[key]

            except KeyError:

                try:

                    varname = self.revvarmap[key[-1]]

                except KeyError:

                    # variable isn't used anywhere else, we can't insert security

                    raise Unauthorized()

            ptypes = self.select.defined_vars[varname].stinfo['possibletypes']

            if len(ptypes) > 1:

                # XXX dunno how to handle this

                self.session.error(

                    'cant check security of %s, ambigous type for %s in %s',

                    self.select, varname, key[0]) # key[0] == the rql expression

                raise Unauthorized()

            etype = iter(ptypes).next()

            eschema = self.schema.eschema(etype)

            if not eschema.has_perm(self.session, action):

                rqlexprs = eschema.get_rqlexprs(action)

                if not rqlexprs:

                    raise Unauthorised()

                self.insert_snippets([((varname, 'X'), rqlexprs)])

    def snippet_subquery(self, varmap, transformedsnippet):

        """introduce the given snippet in a subquery"""

        subselect = stmts.Select()

        selectvar, snippetvar = varmap

        subselect.append_selected(n.VariableRef(

            subselect.get_variable(selectvar)))

        aliases = [selectvar]

        subselect.add_restriction(transformedsnippet.copy(subselect))

        stinfo = self.varinfo['stinfo']

        for rel in stinfo['relations']:

            rschema = self.schema.rschema(rel.r_type)

            if rschema.is_final() or (rschema.inlined and

                                      not rel in stinfo['rhsrelations']):

                self.select.remove_node(rel)

                rel.children[0].name = selectvar

                subselect.add_restriction(rel.copy(subselect))

                for vref in rel.children[1].iget_nodes(n.VariableRef):

                    subselect.append_selected(vref.copy(subselect))

                    aliases.append(vref.name)

        if self.u_varname:

            # generate an identifier for the substitution

            argname = subselect.allocate_varname()

            while argname in self.kwargs:

                argname = subselect.allocate_varname()

            subselect.add_constant_restriction(subselect.get_variable(self.u_varname),

                                               'eid', unicode(argname), 'Substitute')

            self.kwargs[argname] = self.session.user.eid

        add_types_restriction(self.schema, subselect, subselect,

                              solutions=self.solutions)

        myunion = stmts.Union()

        myunion.append(subselect)

        aliases = [n.VariableRef(self.select.get_variable(name, i))

                   for i, name in enumerate(aliases)]

        self.select.add_subquery(n.SubQuery(aliases, myunion), check=False)

        self._cleanup_inserted(transformedsnippet)

        try:

            self.compute_solutions()

        except Unsupported:

            # some solutions have been lost, can't apply this rql expr

            self.select.remove_subquery(new, undefine=True)

            raise

        return subselect

    def remove_ambiguities(self, snippets, newsolutions):

        # the snippet has introduced some ambiguities, we have to resolve them

        # "manually"

        variantes = self.build_variantes(newsolutions)

        # insert "is" where necessary

        varexistsmap = {}

        self.removing_ambiguity = True

        for (erqlexpr, varmap, oldvarname), etype in variantes[0].iteritems():

            varname = self.rewritten[(erqlexpr, varmap, oldvarname)]

            var = self.select.defined_vars[varname]

            exists = var.references()[0].scope

            exists.add_constant_restriction(var, 'is', etype, 'etype')

            varexistsmap[varmap] = exists

        # insert ORED exists where necessary

        for variante in variantes[1:]:

            self.insert_snippets(snippets, varexistsmap)

            for key, etype in variante.iteritems():

                varname = self.rewritten[key]

                try:

                    var = self.select.defined_vars[varname]

                except KeyError:

                    # not a newly inserted variable

                    continue

                exists = var.references()[0].scope

                exists.add_constant_restriction(var, 'is', etype, 'etype')

        # recompute solutions

        #select.annotated = False # avoid assertion error

        self.compute_solutions()

        # clean solutions according to initial solutions

        return remove_solutions(self.solutions, self.select.solutions,

                                self.select.defined_vars)

    def build_variantes(self, newsolutions):

        variantes = set()

        for sol in newsolutions:

            variante = []

            for key, newvar in self.rewritten.iteritems():

                variante.append( (key, sol[newvar]) )

            variantes.add(tuple(variante))

        # rebuild variantes as dict

        variantes = [dict(variante) for variante in variantes]

        # remove variable which have always the same type

        for key in self.rewritten:

            it = iter(variantes)

            etype = it.next()[key]

            for variante in it:

                if variante[key] != etype:

                    break

            else:

                for variante in variantes:

                    del variante[key]

        return variantes

    def _cleanup_inserted(self, node):

        # cleanup inserted variable references

        for vref in node.iget_nodes(n.VariableRef):

            vref.unregister_reference()

            if not vref.variable.stinfo['references']:

                # no more references, undefine the variable

                del self.select.defined_vars[vref.name]

    def _may_be_shared(self, relation, target, searchedvarname):

        """return True if the snippet relation can be skipped to use a relation

        from the original query

        """

        # if cardinality is in '?1', we can ignore the relation and use variable

        # from the original query

        rschema = self.schema.rschema(relation.r_type)

        if target == 'object':

            cardindex = 0

            ttypes_func = rschema.objects

            rprop = rschema.rproperty

        else: # target == 'subject':

            cardindex = 1

            ttypes_func = rschema.subjects

            rprop = lambda x, y, z: rschema.rproperty(y, x, z)

        for etype in self.varinfo['stinfo']['possibletypes']:

            for ttype in ttypes_func(etype):

                if rprop(etype, ttype, 'cardinality')[cardindex] in '+*':

                    return False

        return True

    def _use_outer_term(self, snippet_varname, term):

        key = (self.current_expr, self.varmap, snippet_varname)

        if key in self.rewritten:

            insertedvar = self.select.defined_vars.pop(self.rewritten[key])

            for inserted_vref in insertedvar.references():

                inserted_vref.parent.replace(inserted_vref, term.copy(self.select))

        self.rewritten[key] = term.name

    def _get_varname_or_term(self, vname):

        if vname == 'U':

            if self.u_varname is None:

                select = self.select

                self.u_varname = select.allocate_varname()

                # generate an identifier for the substitution

                argname = select.allocate_varname()

                while argname in self.kwargs:

                    argname = select.allocate_varname()

                # insert "U eid %(u)s"

                var = select.get_variable(self.u_varname)

                select.add_constant_restriction(select.get_variable(self.u_varname),

                                                'eid', unicode(argname), 'Substitute')

                self.kwargs[argname] = self.session.user.eid

            return self.u_varname