"""Shared ring layout; keep in sync with common_cpp/ipc/src/shm_ring.cpp."""

from pathlib import Path
import struct

MAGIC = b"RDRRING2"
VERSION = 1
HEADER = struct.Struct("<8sIIIIQQQ16x")
SLOT_HEADER_SIZE = 16


def ring_path(name: str) -> Path:
    if not name.startswith("/") or len(name) < 2 or "/" in name[1:] or "\x00" in name:
        raise ValueError("ring_name must be '/' followed by a single nonempty filename")
    return Path("/dev/shm") / name[1:]