"""Helpers for the shared skb mark layout used for packet correlation and verdict hints."""

from __future__ import annotations

from typing import Optional


PACKET_ID_MASK = 0x0FFFFFFF
VERDICT_MASK = 0xF0000000
VERDICT_FLAG_DROP = 0x10000000
VERDICT_FLAG_REJECT = 0x20000000


def normalize_skb_mark(value: object) -> Optional[int]:
    """Return a positive integer skb mark or `None` when the value is empty."""
    if value in (None, "", 0, "0"):
        return None
    try:
        mark = int(value)
    except (TypeError, ValueError):
        return None
    if mark < 0:
        mark &= 0xFFFFFFFF
    return mark or None


def packet_id_from_mark(value: object) -> Optional[str]:
    """Extract the packet correlation identifier from the shared skb mark layout."""
    mark = normalize_skb_mark(value)
    if mark is None:
        return None
    packet_id = mark & PACKET_ID_MASK
    return str(packet_id) if packet_id else None


def verdict_from_mark(value: object) -> Optional[str]:
    """Return a verdict hint encoded into the upper mark bits, if any."""
    mark = normalize_skb_mark(value)
    if mark is None:
        return None
    verdict_bits = mark & VERDICT_MASK
    if verdict_bits & VERDICT_FLAG_REJECT:
        return "reject"
    if verdict_bits & VERDICT_FLAG_DROP:
        return "drop"
    return None