"""Composition read boundary, independent of optional audition/reference tools."""
from __future__ import annotations
import contextlib
import contextvars
import os
import pathlib
import sys

ACTIVE = contextvars.ContextVar('composition_reads', default=None)

def _read(event, args):
  scope = ACTIVE.get()
  if scope is None or event != 'open':
    return
  name, mode, flags = args
  if not isinstance(name, (str, bytes, os.PathLike)):
    return
  # r+ and w+ can read; they must obey the same boundary as a plain read.
  if flags & os.O_WRONLY:
    return
  path = pathlib.Path(os.fsdecode(name)).resolve()
  data, code, cache, reads = scope
  python_runtime = any(path.is_relative_to(pathlib.Path(root).resolve()) for root in (sys.base_prefix, sys.prefix))
  allowed = path.is_relative_to(data) or path.is_relative_to(code) or python_runtime
  if cache and path.is_relative_to(cache):
    allowed = True
  if not allowed:
    raise ValueError('Forbidden composition input: ' + str(path))
  reads.add(str(path))

sys.addaudithook(_read)

@contextlib.contextmanager
def composition(data, role, cache=None):
  reads = set()
  code = pathlib.Path(__file__).resolve().parent
  token = ACTIVE.set((pathlib.Path(data).resolve(), code, pathlib.Path(cache).resolve() / role if cache else None, reads))
  try:
    yield reads
  finally:
    ACTIVE.reset(token)