from __future__ import annotations

from typing import List

from .canonical import CanonicalPlan
from .protocol import PlanDelta


def optimize_across_shards(plans: List[CanonicalPlan], bandwidth_budget: float) -> PlanDelta:
    """A tiny, ADMM-lite stub that combines local canonical plans into a delta.

    This is intentionally lightweight for MVP: it aggregates projections and
    predicates and emits a delta with a simple cost summary. Real implementations
    would iterate with cross-shard feedback to refine the plan.
    """
    # Very basic aggregation: union of projections/predicates; cost is sum of costs
    all_projections = []
    all_predicates = []
    total_cost = 0.0
    for p in plans:
        all_projections.extend(p.projection)
        all_predicates.extend(p.predicates)
        total_cost += max(0.0, p.estimated_cost)

    delta = {
        "projections": list(dict.fromkeys(all_projections)),  # unique preserve order
        "predicates": list(dict.fromkeys(all_predicates)),
        "aggregated_cost": total_cost,
        "bandwidth_budget": bandwidth_budget,
    }

    # Simple delta_id and timestamp placeholders; in real use, attach metadata
    return PlanDelta(delta_id="delta-0", timestamp=0.0, changes=delta, contract_id="catopt-bridge")