// The runtime that launched this bundle, as one channel of requests (novox/hq ADR 0193, ADR 0198): what a module's code
// asks of its node's tool runner beyond emitting, subscribing and its state, each named by the runtime's method
// (`mesh/seat.publish`, `mesh/provision.get`). The stdio session binds it when the runtime launched the process; a
// bundle never names a transport.

/** What the runtime is asked through: the stdio session provides it. */
export type RuntimeAsk = (method: string, params: unknown) => Promise<unknown>;

let bound: RuntimeAsk | undefined;

/** Bind the channel. The stdio session calls this when the runtime launched the process; a test binds its own. */
export function useRuntime(ask: RuntimeAsk | undefined): void {
  bound = ask;
  words = undefined;
}

/** The call a bundle reads its tool runner's capability words with: answered with `{words}` (design 47 G §576, §622). */
export const CAPABILITIES_CALL = "mesh/capabilities";
/** The word of the acknowledged publish and the subscription for new messages the finding writer uses (§559). */
export const CAP_FINDING_CALLS = "finding-calls";
/** The code of a runtime's answer to a call it does not know (JSON-RPC's method not found). */
const CODE_NO_METHOD = -32601;

// The words the tool runner states, asked once at the first call that needs one and kept for as long as the bundle runs: a
// bundle lives no longer than the tool runner that started it (design 47 G §576).
let words: Promise<string[]> | undefined;

async function readWords(): Promise<string[]> {
  try {
    const a = (await askRuntime(CAPABILITIES_CALL, {})) as { words?: string[] } | null;
    return a?.words ?? [];
  } catch (e) {
    // a tool runner of before G answers the call as an unknown one, which reads as no word stated
    if ((e as { code?: number }).code === CODE_NO_METHOD) return [];
    throw new Error(`reading the tool runner's capability words: ${e instanceof Error ? e.message : String(e)}`);
  }
}

/**
 * Fail at once, naming the word and the node (from MESH_NODE), when the tool runner this bundle runs under does not state
 * `word`; the words are read once (design 47 G §488, §576). A failed read is asked again at the next call.
 */
export async function requireCapability(word: string): Promise<void> {
  const reading = (words ??= readWords());
  let stated: string[];
  try {
    stated = await reading;
  } catch (e) {
    if (words === reading) words = undefined;
    throw e;
  }
  if (stated.includes(word)) return;
  throw new Error(`the tool runner of node ${process.env.MESH_NODE || "unknown"} does not state the capability word "${word}": a call of its family is refused until it does`);
}

/** Ask the runtime one of its methods; refused with the reason when no runtime launched this bundle. */
export async function askRuntime(method: string, params: unknown): Promise<unknown> {
  if (!bound) {
    throw new Error(`no runtime to ask ${method} of: it is reached through the runtime that launched this bundle (novox/hq ADR 0198)`);
  }
  return bound(method, params);
}

/**
 * Submit an accept, or say an event, on a seat (novox/hq ADR 0259 §3): `subject` whole, as the seat's contract names
 * it (`mesh.seat.<seat>.event.<event>`), de-duplicated by `id` (the same id twice is one message; empty is the
 * runtime's to make). The runtime does it as this module, only as far as its membership lists, and refuses the rest
 * with the reason: the Go side's `stdio.SeatPublish`.
 */
export async function seatPublish(subject: string, body: unknown, id = ""): Promise<void> {
  await askRuntime("mesh/seat.publish", { subject, body, id });
}

/** This module's config value `key`, as mesh-config resolved it for this machine (the Go side's `stdio.Config`). */
export async function config(key: string): Promise<unknown> {
  return askRuntime("mesh/provision.get", { kind: "config", key });
}