"""Locate the 40250 reference source tree for the audit scripts.

Order: `MT_40250_SOURCE` env var, then `reference_root` in `audit/manifest.json`
(relative to the repository root). A missing tree is an error, never a silent fallback.
"""

from __future__ import annotations

import json
import os
from pathlib import Path


def repo_root() -> Path:
    return Path(__file__).resolve().parents[4]


def reference_root(repo: Path | None = None) -> Path:
    repo = (repo or repo_root()).resolve()
    raw = os.environ.get("MT_40250_SOURCE")
    if not raw:
        manifest = json.loads((repo / "audit" / "manifest.json").read_text(encoding="utf-8"))
        raw = manifest.get("reference_root", "")
    if not raw:
        raise SystemExit("40250 reference root not set: export MT_40250_SOURCE or set manifest reference_root")
    path = Path(raw)
    path = (path if path.is_absolute() else repo / path).resolve()
    if not (path / "UserInterface").is_dir():
        raise SystemExit(f"40250 reference root not found or incomplete: {path}")
    return path