from typing import Dict, Any, Tuple

def _safe_eval(expr: str, context: Dict[str, Any]) -> bool:
    if not expr:
        return True
    allowed_globals = {"__builtins__": {}}
    local = dict(context)
    try:
        return bool(eval(expr, allowed_globals, local))
    except Exception:
        return False


class PolicyEngine:
    def __init__(self, contract=None):
        self.contract = contract

    def set_contract(self, contract) -> None:
        self.contract = contract

    def evaluate_pre(self, action: Dict[str, Any], context: Dict[str, Any]) -> Tuple[bool, str]:
        if not self.contract or not self.contract.pre:
            return True, "no-precondition"
        ok = _safe_eval(self.contract.pre, {**context, "action": action})
        return (bool(ok), "precondition" if ok else "precondition-failed")

    def evaluate_post(self, action: Dict[str, Any], context: Dict[str, Any]) -> Tuple[bool, str]:
        if not self.contract or not self.contract.post:
            return True, "no-postcondition"
        ok = _safe_eval(self.contract.post, {**context, "action": action})
        return (bool(ok), "postcondition" if ok else "postcondition-failed")

    def remaining_budgets(self, context: Dict[str, Any]) -> Dict[str, float]:
        budgets = dict(self.contract.budgets) if self.contract and self.contract.budgets else {}
        spent = context.get("spent", {"time": 0, "energy": 0, "compute": 0})
        remaining = {}
        for k, v in budgets.items():
            spent_k = spent.get(k, 0)
            remaining[k] = max(0.0, v - spent_k)
        return remaining