"""Keep heavy jobs (embedding) off reserved cores and at low priority.

The foreground game keeps its cores; this process is pinned to the rest and niced
down so it yields on any shared core. Linux-only affinity is applied when present.
"""

from __future__ import annotations

import os
from collections.abc import Sequence

from . import config


def isolate(
    *,
    allowed: Sequence[int] | None = None,
    nice_increment: int | None = None,
) -> list[int]:
    """Pin this process to `allowed` cores and lower its priority.

    Returns the cores it was pinned to. No-ops the affinity call on platforms
    without ``os.sched_setaffinity`` (non-Linux).
    """
    cores = list(config.ALLOWED_CORES if allowed is None else allowed)
    increment = config.NICE_INCREMENT if nice_increment is None else nice_increment

    set_affinity = getattr(os, "sched_setaffinity", None)
    if set_affinity is not None:
        set_affinity(0, set(cores))
    if increment and hasattr(os, "nice"):
        os.nice(increment)
    return cores