Mini Shell

# Copyright 2015, Tresys Technology, LLC
# Copyright 2018, Chris PeBenito <pebenito@ieee.org>
#
# SPDX-License-Identifier: LGPL-2.1-only
#
from collections import defaultdict
from typing import NamedTuple, Set, Union

from ..policyrep import Type, TypeAttribute, TypeOrAttr

from .descriptors import DiffResultDescriptor
from .difference import Difference, SymbolWrapper
from .typeattr import typeattr_wrapper_factory
from .typing import SymbolCache

_types_cache: SymbolCache[Type] = defaultdict(dict)


class ModifiedType(NamedTuple):

    """Difference details for a modified type."""

    added_attributes: Set[TypeAttribute]
    removed_attributes: Set[TypeAttribute]
    matched_attributes: Set[TypeAttribute]
    modified_permissive: bool
    permissive: bool
    added_aliases: Set[str]
    removed_aliases: Set[str]
    matched_aliases: Set[str]


def type_wrapper_factory(type_: Type) -> SymbolWrapper[Type]:
    """
    Wrap types from the specified policy.

    This caches results to prevent duplicate wrapper
    objects in memory.
    """
    try:
        return _types_cache[type_.policy][type_]
    except KeyError:
        t = SymbolWrapper(type_)
        _types_cache[type_.policy][type_] = t
        return t


def type_or_attr_wrapper_factory(type_: TypeOrAttr) -> \
        Union[SymbolWrapper[Type], SymbolWrapper[TypeAttribute]]:

    """
    Wrap types or attributes from the specified policy.

    This caches results to prevent duplicate wrapper
    objects in memory.
    """
    if isinstance(type_, Type):
        return type_wrapper_factory(type_)
    else:
        return typeattr_wrapper_factory(type_)


class TypesDifference(Difference):

    """Determine the difference in types between two policies."""

    added_types = DiffResultDescriptor("diff_types")
    removed_types = DiffResultDescriptor("diff_types")
    modified_types = DiffResultDescriptor("diff_types")

    def diff_types(self) -> None:
        """Generate the difference in types between the policies."""

        self.log.info(
            "Generating type differences from {0.left_policy} to {0.right_policy}".format(self))

        self.added_types, self.removed_types, matched_types = self._set_diff(
            (SymbolWrapper(t) for t in self.left_policy.types()),
            (SymbolWrapper(t) for t in self.right_policy.types()))

        self.modified_types = dict()

        for left_type, right_type in matched_types:
            # Criteria for modified types
            # 1. change to attribute set, or
            # 2. change to alias set, or
            # 3. different permissive setting
            added_attr, removed_attr, matched_attr = self._set_diff(
                (SymbolWrapper(a) for a in left_type.attributes()),
                (SymbolWrapper(a) for a in right_type.attributes()))

            added_aliases, removed_aliases, matched_aliases = self._set_diff(left_type.aliases(),
                                                                             right_type.aliases(),
                                                                             unwrap=False)

            left_permissive = left_type.ispermissive
            right_permissive = right_type.ispermissive
            mod_permissive = left_permissive != right_permissive

            if added_attr or removed_attr or added_aliases or removed_aliases or mod_permissive:
                self.modified_types[left_type] = ModifiedType(added_attr,
                                                              removed_attr,
                                                              matched_attr,
                                                              mod_permissive,
                                                              left_permissive,
                                                              added_aliases,
                                                              removed_aliases,
                                                              matched_aliases)

    #
    # Internal functions
    #
    def _reset_diff(self) -> None:
        """Reset diff results on policy changes."""
        self.log.debug("Resetting type differences")
        self.added_types = None
        self.removed_types = None
        self.modified_types = None