"""What every operation shares: the refusal it raises and the lookups into `state`."""

from __future__ import annotations

from typing import Any


class OpError(Exception):
    """
    An operation refused, with enough for any adapter to report it.

    `status` is an HTTP code because one adapter needs one; the others ignore it.
    `extra` carries the "here is what would have worked" payload — a bare "no
    such group" leaves an operator guessing at a UUID.
    """

    def __init__(self, message: str, *, status: int = 400,
                 extra: dict[str, Any] | None = None):
        super().__init__(message)
        self.message = message
        self.status = status
        self.extra = extra or {}

    def as_dict(self) -> dict:
        return {"error": self.message, **self.extra}


# ── Shared lookups ───────────────────────────────────────────────────────────

def _roster(state: dict):
    roster = state.get("roster")
    if not roster:
        raise OpError("Roster not available", status=503)
    return roster


def _hub(state: dict):
    hub = state.get("hub")
    if not hub or not hub._session:
        raise OpError("Hub not connected", status=503)
    return hub


def _group_ctx(state: dict, group_id: str) -> dict:
    groups_ctx = state.get("groups_ctx", {})
    if group_id not in groups_ctx:
        raise OpError("Group not hosted on this node", status=404,
                      extra={"available": [
                          {"id": gid} for gid in groups_ctx]})
    return groups_ctx[group_id]


def _config(state: dict):
    config = state.get("config")
    if not config:
        raise OpError("No config loaded", status=503)
    return config