import { Request, Response } from "express";
import http from "http";

const VITE_HOST = "127.0.0.1";
const VITE_PORT = 5199;

// 这些 header 需要从代理响应中剔除（hop-by-hop）
const HOP_BY_HOP = new Set([
  "transfer-encoding",
  "connection",
  "keep-alive",
  "proxy-connection",
  "proxy-authenticate",
  "proxy-authorization",
  "te",
  "trailers",
  "upgrade",
]);

/**
 * 将 /preview/* 请求代理到 Vite dev server。
 * 对 HTML 响应自动重写路径，给所有根绝对路径加上 /ads/preview/ 前缀，
 * 确保浏览器通过 nginx 正确加载资源。
 */
export function previewProxy(req: Request, res: Response): void {
  // Express mount 会剥离 /preview 前缀，req.url 即 Vite 需要的路径
  const targetPath = req.url || "/";
  console.log(`[preview:proxy] ${req.method} ${targetPath}`);

  // 过滤请求 headers（去掉 hop-by-hop、条件缓存头，设置正确的 host）
  const reqHeaders: Record<string, string> = {};
  for (const [key, value] of Object.entries(req.headers)) {
    if (value === undefined) continue;
    const lk = key.toLowerCase();
    if (lk === "host") continue;
    if (lk === "connection" || lk === "keep-alive" || lk === "upgrade") continue;
    // 强制完整响应，避免 304 缓存导致 HTML 无法被重写
    if (lk === "if-none-match" || lk === "if-modified-since" || lk === "cache-control") continue;
    reqHeaders[key] = Array.isArray(value) ? value.join(", ") : value;
  }
  reqHeaders["host"] = `${VITE_HOST}:${VITE_PORT}`;
  reqHeaders["cache-control"] = "no-cache";

  const proxyReq = http.request(
    {
      hostname: VITE_HOST,
      port: VITE_PORT,
      path: targetPath,
      method: req.method,
      headers: reqHeaders,
    },
    (proxyRes) => {
      const contentType = (proxyRes.headers["content-type"] || "") as string;
      const isText = contentType.includes("text/html") ||
                     contentType.includes("text/javascript") ||
                     contentType.includes("application/javascript");
      console.log(`[preview:proxy] response ${proxyRes.statusCode} content-type=${contentType} isText=${isText}`);

      // 复制响应 headers（过滤 hop-by-hop）
      const resHeaders: Record<string, string> = {};
      for (const [key, value] of Object.entries(proxyRes.headers)) {
        if (HOP_BY_HOP.has(key.toLowerCase())) continue;
        if (value !== undefined && value !== null) {
          resHeaders[key] = Array.isArray(value) ? value.join(", ") : value;
        }
      }

      res.status(proxyRes.statusCode || 200);

      if (isText) {
        const chunks: Buffer[] = [];
        proxyRes.on("data", (chunk: Buffer) => chunks.push(chunk));
        proxyRes.on("end", () => {
          let body = Buffer.concat(chunks).toString("utf-8");

          // 重写 HTML (src="/...", href="/...") 和 JS (from "/...", import "/...")
          // 为 /ads/preview/...（跳过已有前缀的，支持单双引号）
          body = body.replace(
            /((?:src|href)=["']|(?:from|import)\s*["'])\/(?!ads\/preview\/)([^"']+)(["'])/g,
            '$1/ads/preview/$2$3',
          );

          // 日志
          if (contentType.includes("text/html")) {
            const viteClientMatch = body.match(/src="[^"]*@vite\/client[^"]*"/);
            console.log(`[preview:proxy] HTML vite/client: ${viteClientMatch?.[0] || "NOT FOUND"}`);
          }

          resHeaders["content-type"] = contentType.includes("text/html")
            ? "text/html; charset=utf-8"
            : contentType;
          resHeaders["content-length"] = String(Buffer.byteLength(body, "utf-8"));
          res.set(resHeaders);
          res.send(body);
        });
      } else {
        res.set(resHeaders);
        proxyRes.pipe(res);
      }
    },
  );

  proxyReq.on("error", (err) => {
    console.error(`[preview:proxy] ${err.message}`);
    if (!res.headersSent) {
      res.status(502).json({ error: "Preview server not available" });
    }
  });

  // POST/PUT/PATCH 请求需要转发 body
  if (req.method === "POST" || req.method === "PUT" || req.method === "PATCH") {
    req.pipe(proxyReq);
  } else {
    proxyReq.end();
  }
}