from __future__ import annotations

from datetime import datetime
from .core import LocalArbProblem, SharedSignals


class PlanDelta:
    def __init__(self, actions, timestamp: datetime | None = None):
        self.actions = actions
        self.timestamp = timestamp or datetime.utcnow()


def admm_step(local: LocalArbProblem, signals: SharedSignals) -> PlanDelta:
    """Deterministic, minimal ADMM-like step producing a single PlanDelta.

    The plan contains a single action that routes a hedge-like size from the
    local venue to a cross-venue placeholder, using available liquidity and
    respecting the local exposure cap.
    """
    # Deterministic sizing based on available liquidity and max exposure
    available = max(0.0, float(signals.liquidity))
    size = min(float(local.max_exposure), available * 0.5)

    action = {
        "venue_from": local.venue,
        "venue_to": "CROSS-VENUE",
        "instrument": local.asset_pair,
        "size": size,
        "time": datetime.utcnow().isoformat() + "Z",
    }

    return PlanDelta(actions=[action])


__all__ = ["PlanDelta", "admm_step"]