"""Delta signing utilities for BeVault MVP."""
from __future__ import annotations
import hmac
import hashlib
from .core import HedgeDelta


def sign_delta(delta: HedgeDelta, key: bytes) -> str:
    """Sign a HedgeDelta deterministically using HMAC-SHA256.

    The signature is derived from the delta contents (asset, hedge_size, timestamp, policy_tag).
    The resulting hex digest is stable for identical inputs and keys.
    """
    payload = f"{delta.asset}:{delta.hedge_size}:{delta.timestamp}:{delta.policy_tag}"
    return hmac.new(key, payload.encode("utf-8"), hashlib.sha256).hexdigest()


__all__ = ["sign_delta"]