import { NextResponse, type NextRequest } from "next/server";
import { TOKEN_COOKIE, REFRESH_COOKIE, CSRF_COOKIE } from "@/lib/cookies";

// SSR 登录态保障：
// access token（j13_token，15 分钟）过期后，页面/RSC 请求到达时先在此静默轮转，
// 新 cookie 同时①注入本次请求头供 layout 的 /api/me 使用 ②透传给浏览器。
// refresh token 是一次性轮转（旧的立即吊销），而 RSC 预取与真实导航、甚至多
// 运行时实例可能几乎同时发起轮转：
//   - 同一实例内用 in-flight Promise 去重（只合并进行中的请求，失败不缓存）；
//   - 跨实例的重复请求由后端宽限期兜底（返回同一个新 token 对）。

// 服务端专用地址；边缘部署（如 Cloudflare Workers）必须通过 BACKEND_URL /
// NEXT_PUBLIC_API_URL 显式配置（生产构建不保留 localhost 兜底，避免在边缘
// 环境发起必然失败的请求；未配置时放行，由客户端 fetchWithRefresh 兜底）。
const API_BASE =
  process.env.BACKEND_URL ||
  process.env.NEXT_PUBLIC_API_URL ||
  (process.env.NODE_ENV === "production" ? "" : "http://localhost:3001");
const EXP_SKEW_SECONDS = 30; // 提前 30s 视为过期，规避服务端时钟差
const REFRESH_TIMEOUT_MS = 8000;

type RefreshResult = { ok: boolean; setCookies: string[] };

// 进行中的轮转表：key 为 refresh token 的 SHA-256（不持有明文），
// 请求结束即删除，失败结果绝不缓存
const inflight = new Map<string, Promise<RefreshResult>>();

function isAccessTokenExpired(token: string | undefined): boolean {
  if (!token) return true;
  try {
    const seg = token.split(".")[1]?.replace(/-/g, "+").replace(/_/g, "/");
    if (!seg) return true;
    const payload = JSON.parse(atob(seg)) as { exp?: number };
    // 只读取过期时间，验签由后端负责
    return typeof payload.exp !== "number"
      ? true
      : Date.now() >= (payload.exp - EXP_SKEW_SECONDS) * 1000;
  } catch {
    return true;
  }
}

async function hashToken(token: string): Promise<string> {
  const data = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(token));
  return Array.from(new Uint8Array(data), (b) => b.toString(16).padStart(2, "0")).join("");
}

// 从合并形式的 set-cookie 头中拆出多条（部分运行时没有 headers.getSetCookie()）。
// Expires 属性格式含 ", "，不能直接按逗号切分：只有顶层段是 "非属性名=..."
// 才是一条新 cookie 的开始，其余片段拼回上一条。
const COOKIE_ATTR_NAMES = new Set([
  "expires",
  "max-age",
  "domain",
  "path",
  "samesite",
  "secure",
  "httponly",
  "priority",
]);

function splitCombinedSetCookie(raw: string): string[] {
  const segments = raw.split(", ");
  const cookies: string[] = [];
  for (const seg of segments) {
    const pair = seg.split(";", 1)[0] ?? "";
    const eq = pair.indexOf("=");
    const name = eq > 0 ? pair.slice(0, eq).trim().toLowerCase() : "";
    if (eq > 0 && name && !COOKIE_ATTR_NAMES.has(name)) {
      cookies.push(seg);
    } else if (cookies.length > 0) {
      cookies[cookies.length - 1] += ", " + seg;
    }
  }
  return cookies;
}

function readSetCookies(res: Response): string[] {
  const headers = res.headers as unknown as {
    getSetCookie?: () => string[];
  };
  if (typeof headers.getSetCookie === "function") {
    try {
      const list = headers.getSetCookie();
      if (list.length > 0) return list;
    } catch {
      // 落到手动解析
    }
  }
  const raw = res.headers.get("set-cookie");
  return raw ? splitCombinedSetCookie(raw) : [];
}

async function doRotate(refreshToken: string, csrf: string): Promise<RefreshResult> {
  const res = await fetch(`${API_BASE}/api/auth/refresh`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "X-CSRF-Token": csrf,
      Cookie: `${REFRESH_COOKIE}=${refreshToken}; ${CSRF_COOKIE}=${csrf}`,
    },
    cache: "no-store",
    signal: AbortSignal.timeout(REFRESH_TIMEOUT_MS),
  }).catch(() => null);

  if (!res) return { ok: false, setCookies: [] };
  // 成功=新三枚 cookie；失败（refresh 过期/被吊销）=后端下发的清除指令
  const setCookies = readSetCookies(res);
  return { ok: res.ok && setCookies.length > 0, setCookies };
}

// 同一 refresh token 的并发请求共享同一个进行中的 Promise（完成即删除，不缓存结果）
async function rotateRefreshToken(refreshToken: string, csrf: string): Promise<RefreshResult> {
  const key = await hashToken(refreshToken);
  const existing = inflight.get(key);
  if (existing) return existing;
  const p = doRotate(refreshToken, csrf).finally(() => {
    inflight.delete(key);
  });
  inflight.set(key, p);
  return p;
}

// 从 Set-Cookie 头提取 name=value
function parseCookiePair(setCookie: string): [string, string] | null {
  const pair = setCookie.split(";", 1)[0] ?? "";
  const eq = pair.indexOf("=");
  if (eq <= 0) return null;
  return [pair.slice(0, eq).trim(), pair.slice(eq + 1).trim()];
}

/** 透传 pathname 给根布局，用于 /admin 与公开站 chrome 分叉 */
function withPathname(req: NextRequest, init?: { request?: { headers: Headers } }) {
  const headers = new Headers(init?.request?.headers ?? req.headers);
  headers.set("x-pathname", req.nextUrl.pathname);
  return NextResponse.next({ request: { headers } });
}

export async function middleware(req: NextRequest) {
  const refreshToken = req.cookies.get(REFRESH_COOKIE)?.value;
  const accessToken = req.cookies.get(TOKEN_COOKIE)?.value;

  // 游客、access 仍有效、或服务端地址未配置：直接放行
  if (!refreshToken || !isAccessTokenExpired(accessToken) || !API_BASE) {
    return withPathname(req);
  }

  const csrf = req.cookies.get(CSRF_COOKIE)?.value ?? "";

  try {
    const { ok, setCookies } = await rotateRefreshToken(refreshToken, csrf);

    if (ok) {
      // 以旧 jar 为基础覆盖轮转结果，保证本次 SSR 的 cookies() 读到新 access
      const jar = new Map<string, string>();
      req.cookies.getAll().forEach((c) => jar.set(c.name, c.value));
      for (const sc of setCookies) {
        const parsed = parseCookiePair(sc);
        if (parsed) jar.set(parsed[0], parsed[1]);
      }
      const headers = new Headers(req.headers);
      headers.set("Cookie", [...jar].map(([k, v]) => `${k}=${v}`).join("; "));

      const res = withPathname(req, { request: { headers } });
      // 原样透传，HttpOnly/Path/SameSite/Secure 等属性全部以后端为准
      for (const sc of setCookies) res.headers.append("Set-Cookie", sc);
      return res;
    }

    if (setCookies.length > 0) {
      // refresh 已失效：透传后端的清 cookie 指令，避免之后每次请求都白轮转
      const res = withPathname(req);
      for (const sc of setCookies) res.headers.append("Set-Cookie", sc);
      return res;
    }
  } catch {
    // 后端不可达：降级匿名渲染，客户端 fetchWithRefresh 仍可兜底
  }

  return withPathname(req);
}

export const config = {
  // 仅拦截页面与 RSC 请求；/api 由客户端 fetchWithRefresh 处理，静态资源放行
  matcher: [
    "/((?!api/|healthz|_next/static/|_next/image/|favicon.ico|robots.txt|sitemap.xml|.*\\.(?:svg|png|jpg|jpeg|gif|webp|ico|txt|woff2?)$).*)",
  ],
};