# SPDX-License-Identifier: GPL-3.0-or-later
"""DECNET bus interop. Aligns BEHAVE Observation with DECNET Event payload shape.

DECNET's Event (decnet/bus/base.py:26) carries ``(topic, payload, type, v, ts, id)``.
A BEHAVE Observation maps onto that envelope as follows:

    topic   = "attacker.observation." + observation.primitive
    payload = observation.model_dump(exclude={"id", "ts", "v"})
    type    = observation.primitive
    v       = observation.v
    ts      = observation.ts
    id      = observation.id

The publisher must set ``topic`` from the primitive when calling ``bus.publish()``;
DECNET's bus does not trust topic from the wire (anti-spoofing, base.py:60-76).

This module does NOT import DECNET. The adapter speaks dicts; consumers wire it
to their own bus.
"""

from __future__ import annotations

from typing import Any

from .envelope import Observation

TOPIC_PREFIX: str = "attacker.observation"


def event_topic_for(primitive: str) -> str:
    """Return the canonical DECNET bus topic for a BEHAVE primitive."""
    return f"{TOPIC_PREFIX}.{primitive}"


def to_event_payload(obs: Observation) -> dict[str, Any]:
    """Project an Observation into a dict suitable for ``Event.payload``.

    Excludes ``id``, ``ts``, and ``v`` because those are carried at the Event
    envelope level by DECNET, not in the payload body.
    """
    return obs.model_dump(exclude={"id", "ts", "v"}, mode="json")


def from_event_payload(primitive: str, payload: dict[str, Any]) -> Observation:
    """Reconstruct an Observation from ``(topic-derived primitive, Event.payload)``.

    The ``primitive`` argument is the trailing segment of the bus topic, NOT a
    field read from the payload — relying on the wire-side ``primitive`` field
    would let a misbehaving publisher spoof observations on topics they don't
    actually publish to. This mirrors DECNET's ``Event.from_dict`` discipline
    (decnet/bus/base.py:60-76).
    """
    if "primitive" in payload and payload["primitive"] != primitive:
        raise ValueError(
            f"payload.primitive ({payload['primitive']!r}) does not match "
            f"topic-derived primitive ({primitive!r}); refusing to reconstruct"
        )
    return Observation.model_validate({**payload, "primitive": primitive})