# policy.py (loader/utilities for user-supplied policy scripts)
from __future__ import annotations

import importlib.util
import inspect
import os
from types import ModuleType
from typing import Callable, Any


class PolicyLoadError(Exception):
    pass


def _import_module_from_path(path: str) -> ModuleType:
    if not os.path.exists(path):
        raise PolicyLoadError(f"Policy file not found: {path}")
    spec = importlib.util.spec_from_file_location("user_policy", path)
    if spec is None or spec.loader is None:
        raise PolicyLoadError("Could not load policy module spec.")
    mod = importlib.util.module_from_spec(spec)
    try:
        spec.loader.exec_module(mod)  # type: ignore[reportAttributeAccessIssue]
    except Exception as e:
        raise PolicyLoadError(f"Error executing policy module: {e}") from e
    return mod

def default_policy_path() -> str:
    return os.path.join(os.path.dirname(__file__), "default_policy.py")

def load_policy(path: str) -> Callable[..., bool]:
    """
    Load a user policy file and return the `decide` callable.
    """
    mod = _import_module_from_path(path)
    decide = getattr(mod, "decide", None)
    if not callable(decide):
        raise PolicyLoadError("Policy script must define a callable `decide(...)`.")
    return decide


def call_policy(decide: Callable[..., Any], **kwargs: Any) -> Any:
    """
    Call `decide` with only the parameters it accepts.
    This lets us pass new optional context (like p, corr) without breaking old policies.
    """
    sig = inspect.signature(decide)
    accepted = {k: v for k, v in kwargs.items() if k in sig.parameters}
    return decide(**accepted)