"""pytest bootstrap for the PDG regression suite.

Stdlib only. Its sole job is to guarantee a *writable* base temp dir so the
suite runs with the bare command ``python -m pytest tests -q`` on hosts where
the default ``%LOCALAPPDATA%\\Temp`` path is not accessible (e.g. sandboxed
CI). It prefers, in order: an explicit ``--basetemp`` (left untouched), then
``$PYTEST_DEBUG_TEMPROOT``, then a writable ``C:\\tmp`` / ``/tmp``, then the
project's own ``.pytest_tmp`` directory.

This changes only *where* temp dirs live; it never weakens any assertion.
"""

from __future__ import annotations

import os
import sys
import tempfile
from pathlib import Path


def _pick_temproot() -> Path:
    candidates = []
    env = os.environ.get("PYTEST_DEBUG_TEMPROOT")
    if env:
        candidates.append(Path(env))
    # Writable scratch roots common on this host.
    if sys.platform.startswith("win"):
        candidates.append(Path("C:/tmp"))
    else:
        candidates.append(Path("/tmp"))
    # Last-resort: a temp root inside the project tree (always writable).
    candidates.append(Path(__file__).resolve().parent.parent / ".pytest_tmp")

    for c in candidates:
        try:
            c.mkdir(parents=True, exist_ok=True)
            probe = c / ".write_probe"
            probe.write_text("ok", encoding="utf-8")
            probe.unlink()
            return c
        except OSError:
            continue
    # Could not find anything writable; fall back to the system default.
    return Path(tempfile.gettempdir())


# Only override when the user has not already pinned a base temp dir.
if "--basetemp" not in " ".join(sys.argv) and not os.environ.get("PYTEST_DEBUG_TEMPROOT"):
    root = _pick_temproot()
    os.environ["PYTEST_DEBUG_TEMPROOT"] = str(root)