# Copyright 2014-2015, Tresys Technology, LLC
#
# This file is part of SETools.
#
# SETools 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.
#
# SETools 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 SETools.  If not, see
# <http://www.gnu.org/licenses/>.
#
import logging


class PolicyQuery(object):

    """Base class for SELinux policy queries."""

    def __init__(self, policy, **kwargs):
        self.log = logging.getLogger(self.__class__.__name__)

        self.policy = policy

        # keys are sorted in reverse order so regex settings
        # are set before the criteria, e.g. name_regex
        # is set before name.  This ensures correct behavior
        # since the criteria descriptors are sensitve to
        # regex settings.
        for name in sorted(kwargs.keys(), reverse=True):
            attr = getattr(self, name, None)  # None is not callable
            if callable(attr):
                raise ValueError("Keyword parameter {0} conflicts with a callable.".format(name))

            setattr(self, name, kwargs[name])

    @staticmethod
    def _match_regex(obj, criteria, regex):
        """
        Match the object with optional regular expression.

        Parameters:
        obj         The object to match.
        criteria    The criteria to match.
        regex       If regular expression matching should be used.
        """

        if regex:
            return bool(criteria.search(str(obj)))
        else:
            return obj == criteria

    @staticmethod
    def _match_set(obj, criteria, equal):
        """
        Match the object (a set) with optional set equality.

        Parameters:
        obj         The object to match. (a set)
        criteria    The criteria to match. (a set)
        equal       If set equality should be used. Otherwise
                    any set intersection will match.
        """

        if equal:
            return obj == criteria
        else:
            return bool(obj.intersection(criteria))

    @staticmethod
    def _match_in_set(obj, criteria, regex):
        """
        Match if the criteria is in the list, with optional
        regular expression matching.

        Parameters:
        obj         The object to match.
        criteria    The criteria to match.
        regex       If regular expression matching should be used.
        """

        if regex:
            return [m for m in obj if criteria.search(str(m))]
        else:
            return criteria in obj

    @staticmethod
    def _match_indirect_regex(obj, criteria, indirect, regex):
        """
        Match the object with optional regular expression and indirection.

        Parameters:
        obj         The object to match.
        criteria    The criteria to match.
        regex       If regular expression matching should be used.
        indirect    If object indirection should be used, e.g.
                    expanding an attribute.
        """

        if indirect:
            return PolicyQuery._match_in_set((obj.expand()), criteria, regex)
        else:
            return PolicyQuery._match_regex(obj, criteria, regex)

    @staticmethod
    def _match_regex_or_set(obj, criteria, equal, regex):
        """
        Match the object (a set) with either set comparisons
        (equality or intersection) or by regex matching of the
        set members.  Regular expression matching will override
        the set equality option.

        Parameters:
        obj         The object to match. (a set)
        criteria    The criteria to match.
        equal       If set equality should be used.  Otherwise
                    any set intersection will match. Ignored
                    if regular expression matching is used.
        regex       If regular expression matching should be used.
        """

        if regex:
            return [m for m in obj if criteria.search(str(m))]
        else:
            return PolicyQuery._match_set(obj, set(criteria), equal)

    @staticmethod
    def _match_range(obj, criteria, subset, overlap, superset, proper):
        """
        Match ranges of objects.

        obj         An object with attributes named "low" and "high", representing the range.
        criteria    An object with attributes named "low" and "high", representing the criteria.
        subset      If true, the criteria will match if it is a subset obj's range.
        overlap     If true, the criteria will match if it overlaps any of the obj's range.
        superset    If true, the criteria will match if it is a superset of the obj's range.
        proper      If true, use proper superset/subset operations.
                    No effect if not using set operations.
        """

        if overlap:
            return ((obj.low <= criteria.low <= obj.high) or (
                     obj.low <= criteria.high <= obj.high) or (
                     criteria.low <= obj.low and obj.high <= criteria.high))
        elif subset:
            if proper:
                return ((obj.low < criteria.low and criteria.high <= obj.high) or (
                         obj.low <= criteria.low and criteria.high < obj.high))
            else:
                return obj.low <= criteria.low and criteria.high <= obj.high
        elif superset:
            if proper:
                return ((criteria.low < obj.low and obj.high <= criteria.high) or (
                         criteria.low <= obj.low and obj.high < criteria.high))
            else:
                return (criteria.low <= obj.low and obj.high <= criteria.high)
        else:
            return criteria.low == obj.low and obj.high == criteria.high

    @staticmethod
    def _match_level(obj, criteria, dom, domby, incomp):
        """
        Match the an MLS level.

        obj         The level to match.
        criteria    The criteria to match. (a level)
        dom         If true, the criteria will match if it dominates obj.
        domby       If true, the criteria will match if it is dominated by obj.
        incomp      If true, the criteria will match if it is incomparable to obj.
        """

        if dom:
            return (criteria >= obj)
        elif domby:
            return (criteria <= obj)
        elif incomp:
            return (criteria ^ obj)
        else:
            return (criteria == obj)

    def results(self):
        """
        Generator which returns the matches for the query.  This method
        should be overridden by subclasses.
        """
        raise NotImplementedError