export function extractErrorCode(err: unknown): string | undefined {
  if (!err || typeof err !== "object") return undefined;
  const code = (err as { code?: unknown }).code;
  if (typeof code === "string") return code;
  if (typeof code === "number") return String(code);
  return undefined;
}

export function formatErrorMessage(err: unknown): string {
  if (err instanceof Error) {
    return err.message || err.name || "Error";
  }
  if (typeof err === "string") return err;
  if (typeof err === "number" || typeof err === "boolean" || typeof err === "bigint") {
    return String(err);
  }
  try {
    return JSON.stringify(err);
  } catch {
    return Object.prototype.toString.call(err);
  }
}

/** Extract diagnostic detail from a network error's cause chain (e.g. APIConnectionError). */
export function describeNetworkError(err: unknown): string {
  const msg = formatErrorMessage(err);
  const cause = (err as { cause?: unknown })?.cause;
  if (!cause) return msg;
  const code = extractErrorCode(cause);
  const causeMsg = cause instanceof Error ? cause.message : undefined;
  const detail = code ?? causeMsg;
  if (!detail || msg.includes(detail)) return msg;
  return `${msg} (${detail})`;
}

export function formatUncaughtError(err: unknown): string {
  if (extractErrorCode(err) === "INVALID_CONFIG") {
    return formatErrorMessage(err);
  }
  if (err instanceof Error) {
    return err.stack ?? err.message ?? err.name;
  }
  return formatErrorMessage(err);
}