"""Internal OpenFOAM environment resolution for Python scripts.

This keeps user-facing commands rooted in the project .venv while still giving
OpenFOAM subprocesses the environment normally produced by etc/bashrc.
"""

from __future__ import annotations

import os
import shlex
import subprocess
from functools import lru_cache
from pathlib import Path

ROOT = Path(__file__).resolve().parents[1]


@lru_cache(maxsize=1)
def openfoam_env() -> dict[str, str]:
    """Return a sanitized environment with OpenFOAM v14 sourced.

    The returned environment intentionally removes ambient PYTHONPATH. The
    project package is installed into .venv by `uv sync --dev`, so PYTHONPATH is
    unnecessary and can accidentally shadow the venv's binary wheels.
    """

    bashrc = ROOT / "OpenFOAM-14/etc/bashrc"
    if not bashrc.exists():
        raise RuntimeError(f"OpenFOAM bashrc not found: {bashrc}")

    command = " ".join(
        [
            "set +u;",
            "source",
            shlex.quote(str(bashrc)),
            "WM_MPLIB=Dummy",
            "ParaView_TYPE=none",
            "SCOTCH_TYPE=none",
            "ZOLTAN_TYPE=none",
            ">/dev/null;",
            "set -u;",
            "unset FOAM_SIGFPE;",
            "unset PYTHONPATH;",
            "env -0",
        ]
    )
    completed = subprocess.run(
        ["bash", "-lc", command],
        cwd=ROOT,
        check=True,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        env={key: value for key, value in os.environ.items() if key not in {"PYTHONPATH", "FOAM_SIGFPE"}},
    )
    env: dict[str, str] = {}
    for item in completed.stdout.decode().split("\0"):
        if not item:
            continue
        key, _, value = item.partition("=")
        env[key] = value
    env.pop("PYTHONPATH", None)
    env.pop("FOAM_SIGFPE", None)
    return env


def apply_openfoam_env() -> dict[str, str]:
    """Apply and return the sanitized OpenFOAM environment to this process."""

    env = openfoam_env()
    os.environ.update(env)
    os.environ.pop("PYTHONPATH", None)
    os.environ.pop("FOAM_SIGFPE", None)
    return env