"""Blocking disk work the session hands to `off_disk`."""

from pathlib import Path

from meshbay_node.roots import ROOT_NOT_SERVED, RootSet, entry_abs_path


def _locate(roots: RootSet, entry) -> tuple[Path | None, str | None]:
    """
    Where an entry is, and whether it is readable — or the refusal to send.

    Both halves are syscalls: `resolve()` walks the path and `exists()` stats
    it, and a stat is what *wakes* a sleeping disk. Leaving either on the event
    loop and offloading only the read would move the stall rather than remove
    it, and the read would then find the disk already awake. Blocking; called
    through `off_disk`.
    """
    path = entry_abs_path(roots, entry)
    if path is None:
        return None, ROOT_NOT_SERVED
    if not path.exists():
        return None, "File not on disk"
    return path, None