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

tree.

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

"""

__docformat__ = "restructuredtext en"

from rql import nodes as n, stmts, TypeResolverException

from yams import BadSchemaDefinition

from logilab.common.graph import has_path

from cubicweb import Unauthorized, typed_eid

def add_types_restriction(schema, rqlst, newroot=None, solutions=None):

    if newroot is None:

        assert solutions is None

        if hasattr(rqlst, '_types_restr_added'):

            return

        solutions = rqlst.solutions

        newroot = rqlst

        rqlst._types_restr_added = True

    else:

        assert solutions is not None

        rqlst = rqlst.stmt

    eschema = schema.eschema

    allpossibletypes = {}

    for solution in solutions:

        for varname, etype in solution.iteritems():

            if not varname in newroot.defined_vars or eschema(etype).final:

                continue

            allpossibletypes.setdefault(varname, set()).add(etype)

    for varname in sorted(allpossibletypes):

        try:

            var = newroot.defined_vars[varname]

        except KeyError:

            continue

        stinfo = var.stinfo

        if stinfo.get('uidrels'):

            continue # eid specified, no need for additional type specification

        try:

            typerels = rqlst.defined_vars[varname].stinfo.get('typerels')

        except KeyError:

            assert varname in rqlst.aliases

            continue

        if newroot is rqlst and typerels:

            mytyperel = iter(typerels).next()

        else:

            for vref in newroot.defined_vars[varname].references():

                rel = vref.relation()

                if rel and rel.is_types_restriction():

                    mytyperel = rel

                    break

            else:

                mytyperel = None

        possibletypes = allpossibletypes[varname]

        if mytyperel is not None:

            # variable as already some types restriction. new possible types

            # can only be a subset of existing ones, so only remove no more

            # possible types

            for cst in mytyperel.get_nodes(n.Constant):

                if not cst.value in possibletypes:

                    cst.parent.remove(cst)

                    try:

                        stinfo['possibletypes'].remove(cst.value)

                    except KeyError:

                        # restriction on a type not used by this query, may

                        # occurs with X is IN(...)

                        pass

        else:

            # we have to add types restriction

            if stinfo.get('scope') is not None:

                rel = var.scope.add_type_restriction(var, possibletypes)

            else:

                # tree is not annotated yet, no scope set so add the restriction

                # to the root

                rel = newroot.add_type_restriction(var, possibletypes)

            stinfo['typerels'] = frozenset((rel,))

            stinfo['possibletypes'] = possibletypes

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):

    """raised when an rql expression can't be inserted in some rql query

    because it create an unresolvable query (eg no solutions found)

    """

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, existingvars=None):

        """

        snippets: (varmap, list of rql expression)

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

        """

        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 = []

        self.existingvars = existingvars

        # 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)

    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:

                try:

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

                except KeyError:

                    # variable has been moved to a newly inserted subquery

                    # we should insert snippet in that subquery

                    subquery = self.select.aliases[selectvar].query

                    assert len(subquery.children) == 1

                    subselect = subquery.children[0]

                    RQLRewriter(self.session).rewrite(subselect, [(varmap, rqlexprs)],

                                                      subselect.solutions, self.kwargs)

                    continue

                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:

                        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)

        existing = self.existingvars

        self.existingvars = None

        try:

            return self._insert_snippet(varmap, parent, new)

        finally:

            self.existingvars = existing

    def _insert_snippet(self, varmap, parent, new):

        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 Unauthorized()

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

    def snippet_subquery(self, varmap, transformedsnippet):

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

        subselect = stmts.Select()

        selectvar = varmap[0]

        subselectvar = subselect.get_variable(selectvar)

        subselect.append_selected(n.VariableRef(subselectvar))

        snippetrqlst = n.Exists(transformedsnippet.copy(subselect))

        aliases = [selectvar]

        stinfo = self.varinfo['stinfo']

        need_null_test = False

        for rel in stinfo['relations']:

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

            if rschema.final or (rschema.inlined and

                                 not rel in stinfo['rhsrelations']):

                rel.children[0].name = selectvar # XXX explain why

                subselect.add_restriction(rel.copy(subselect))

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

                    if isinstance(vref.variable, n.ColumnAlias):

                        # XXX could probably be handled by generating the subquery

                        # into the detected subquery

                        raise BadSchemaDefinition(

                            "cant insert security because of usage two inlined "

                            "relations in this query. You should probably at "

                            "least uninline %s" % rel.r_type)

                    subselect.append_selected(vref.copy(subselect))

                    aliases.append(vref.name)

                self.select.remove_node(rel)

                # when some inlined relation has to be copied in the subquery,

                # we need to test that either value is NULL or that the snippet

                # condition is satisfied

                if rschema.inlined and rel.optional:

                    need_null_test = True

        if need_null_test:

            snippetrqlst = n.Or(

                n.make_relation(subselectvar, 'is', (None, None), n.Constant,

                                operator='IS'),

                snippetrqlst)

        subselect.add_restriction(snippetrqlst)

        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(self.select.with_[-1])