const LOOPBACK_HOSTS = new Set(["localhost", "127.0.0.1", "[::1]"]);

export function parseMulticaCallbackUrl(value) {
  if (typeof value !== "string" || !value || value.length > 12_000) {
    throw new Error("请粘贴完整的 Multica 回调链接");
  }

  let url;
  try {
    url = new URL(value);
  } catch {
    throw new Error("回调链接格式不正确");
  }

  const port = Number(url.port);
  if (url.protocol !== "http:" || !LOOPBACK_HOSTS.has(url.hostname) || url.pathname !== "/callback") {
    throw new Error("只接受 Multica 生成的 localhost 回调链接");
  }
  if (!Number.isInteger(port) || port < 1024 || port > 65535) {
    throw new Error("回调链接缺少有效端口");
  }
  if (!url.searchParams.get("token") || !url.searchParams.get("state")) {
    throw new Error("回调链接缺少 token 或 state");
  }
  return url;
}

export async function relayMulticaCallback(value, fetchImpl = fetch) {
  const url = parseMulticaCallbackUrl(value);
  const response = await fetchImpl(url, {
    method: "GET",
    redirect: "manual",
    signal: AbortSignal.timeout(8_000),
  });
  if (!response.ok) throw new Error(`Multica 回调未被接受 (${response.status})`);
  return { ok: true };
}