"""Composition read boundary, independent of optional audition/reference tools."""
from __future__ import annotations
import contextlib
import contextvars
import os
from pathlib import Path
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=Path(os.fsdecode(name)).resolve()
  data,code,cache,reads=scope
  python_runtime=any(path.is_relative_to(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=Path(__file__).resolve().parent
  token=ACTIVE.set((Path(data).resolve(),code,Path(cache).resolve()/role if cache else None,reads))
  try:yield reads
  finally:ACTIVE.reset(token)