"""Disk-usage measurement shared by the mount and contention lanes.

Visible bytes (st_size) and allocated bytes (st_blocks * 512) diverge on

lazily-hydrated trees: a mount can show a full-size tree while having

allocated almost nothing. Reporting both is what lets the marginal-disk

claim survive scrutiny; collapsing them would overstate either side.

stat() never reads file content, so walking a lazy mount with this probe

does not itself hydrate data.

"""

from __future__ import annotations

import os

from pathlib import Path

from typing import Any

DEFAULT_MAX_ENTRIES = 200_000

def bounded_tree_usage(root: Path, max_entries: int = DEFAULT_MAX_ENTRIES) -> dict[str, Any]:

    visible_bytes = 0

    allocated_bytes = 0

    entry_count = 0

    truncated = False

    if not root.exists():

        return {

            "visible_tree_bytes": 0,

            "allocated_tree_bytes": 0,

            "disk_entry_count": 0,

            "disk_usage_truncated": False,

            "checks": {"ok": False, "exists": False},

        }

    for dirpath, dirnames, filenames in os.walk(root):

        entry_count += 1

        if entry_count >= max_entries:

            truncated = True

            dirnames[:] = []

            break

        for name in filenames:

            entry_count += 1

            path = Path(dirpath) / name

            try:

                stat = path.lstat()

            except OSError:

                continue

            visible_bytes += stat.st_size

            allocated_bytes += int(getattr(stat, "st_blocks", 0)) * 512

            if entry_count >= max_entries:

                truncated = True

                dirnames[:] = []

                break

    return {

        "visible_tree_bytes": visible_bytes,

        "allocated_tree_bytes": allocated_bytes,

        "disk_entry_count": entry_count,

        "disk_usage_truncated": truncated,

        "checks": {"ok": True, "exists": True},

    }