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"""Utilities for handling privileges."""
import logging
from typing import Union, Sequence, Iterator, TypeAlias
logger = logging.getLogger(__name__)
Operator: TypeAlias = str # Valid operators: "AND", "OR"
Privilege: TypeAlias = str
PrivilegesList: TypeAlias = Sequence[Privilege]
ParseTree = tuple[Operator,
# Leaves (`PrivilegesList` objects) on the left,
# trees (`ParseTree` objects) on the right
Union[PrivilegesList, tuple[PrivilegesList, 'ParseTree']]]
class SpecificationValueError(ValueError):
"""Raised when there is an error in the specification string."""
_OPERATORS_ = ("OR", "AND")
_EMPTY_SPEC_ERROR_ = SpecificationValueError(
"Empty specification. I do not know what to do.")
def __add_leaves__(
index: int,
tree: tuple[Operator],
leaves: dict
) -> Union[tuple[Operator], ParseTree]:
"""Add leaves to the tree."""
if leaves.get(index):
return tree + (leaves[index],)
return tree
def __build_tree__(tree_state: dict) -> ParseTree:
"""Given computed state, build the actual tree."""
_built= []
for idx, tree in enumerate(tree_state["trees"]):
_built.append(__add_leaves__(idx, (tree[2],), tree_state["leaves"]))
logger.debug("Number of built trees: %s, %s", len(_built), _built)
_num_trees = len(_built)
for idx in range(0, _num_trees):
_last_tree = _built.pop()
logger.debug("LAST TREE: %s, %s", _last_tree, len(_last_tree))
if len(_last_tree) <= 1:# Has no leaves or subtrees
_last_tree = None# type: ignore[assignment]
continue# more evil
_name = tree_state["trees"][_num_trees - 1 - idx][0]
_parent = tree_state["trees"][
tree_state["trees"][_num_trees - 1 - idx][1]]
_op = tree_state["trees"][_num_trees - 1 - idx][2]
logger.debug("TREE => name: %s, operation: %s, parent: %s",
_name, _op, _parent)
if _name != _parent[0]:# not root tree
if _op == _parent[2]:
_built[_parent[0]] = (
_built[_parent[0]][0],# Operator
_built[_parent[0]][1] + _last_tree[1]# merge leaves
) + _last_tree[2:]#Add any trees left over
else:
_built[_parent[0]] += (_last_tree,)
if _last_tree is None:
raise _EMPTY_SPEC_ERROR_
return _last_tree
def __parse_tree__(tokens: Iterator[str]) -> ParseTree:
"""Parse the tokens into a tree."""
_state = {
"tokens": [],
"trees": [],#(name, parent, operator, start, end)
"open-parens": 0,
"current-tree": 0,
"leaves": {}#[parent-tree, [index, index, ...]]
}
for _idx, _token in enumerate(tokens):
_state["tokens"].append(_token)
if _idx==0:
if _token[1:].upper() not in _OPERATORS_:
raise SpecificationValueError(f"Invalid operator: {_token[1:]}")
_state["open-parens"] += 1
_state["trees"].append((0, 0, _token[1:].upper(), _idx))
_state["current-tree"] = 0
continue# this is bad!
if _token == ")":# end a tree
logger.debug("ENDING A TREE: %s", _state)
_state["open-parens"] -= 1
_state["trees"][_state["current-tree"]] = (
_state["trees"][_state["current-tree"]] + (_idx,))
# We go back to the parent below.
_state["current-tree"] = _state["trees"][_state["current-tree"]][1]
continue# still really bad!
if _token[1:].upper() in _OPERATORS_:# new child tree
_state["open-parens"] += 1
_state["trees"].append((len(_state["trees"]),
_state["current-tree"],
_token[1:].upper(),
_idx))
_state["current-tree"] = len(_state["trees"]) - 1
continue# more evil still
logger.debug("state: %s", _state)
# leaves
_state["leaves"][_state["current-tree"]] = _state["leaves"].get(
_state["current-tree"], tuple()) + (_token,)
# Build parse-tree from state
if _state["open-parens"] != 0:
raise SpecificationValueError("Unbalanced parentheses.")
return __build_tree__(_state)
def __tokenise__(spec: str) -> Iterator[str]:
"""Clean up and tokenise the string."""
return (token.strip()
for token in spec.replace(
"(", " ("
).replace(
")", " ) "
).replace(
"( ", "("
).split())
def parse(spec: str) -> ParseTree:
"""Parse a string specification for privileges and return a tree of data
objects of the form (<operator> (<check>))"""
if spec.strip() == "":
raise _EMPTY_SPEC_ERROR_
return __parse_tree__(__tokenise__(spec))
def check(spec: str, privileges: tuple[str, ...]) -> bool:
"""Check that the sequence of `privileges` satisfies `spec`."""
_spec = spec
_privs = privileges
return False
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