import { NextRequest } from "next/server";

const BACKEND_URL = process.env.BACKEND_URL || "http://localhost:8000";

export async function GET(req: NextRequest, ctx: { params: Promise<{ path: string[] }> }) {
  const { path } = await ctx.params;
  const url = new URL(req.url);
  const upstream = `${BACKEND_URL}/api/${path.join("/")}${url.search}`;
  return await safeUpstreamFetch(() => fetch(upstream, { headers: forwardHeaders(req) }));
}

export async function POST(req: NextRequest, ctx: { params: Promise<{ path: string[] }> }) {
  const { path } = await ctx.params;
  const url = new URL(req.url);
  const upstream = `${BACKEND_URL}/api/${path.join("/")}${url.search}`;
  const body = await req.text();
  return await safeUpstreamFetch(() =>
    fetch(upstream, {
      method: "POST",
      headers: { ...forwardHeaders(req), "content-type": req.headers.get("content-type") || "application/json" },
      body
    })
  );
}

function forwardHeaders(req: NextRequest) {
  const h = new Headers();
  const auth = req.headers.get("authorization");
  if (auth) h.set("authorization", auth);
  return h;
}

async function forwardResponse(r: Response) {
  const headers = new Headers(r.headers);
  headers.delete("access-control-allow-origin");
  return new Response(await r.arrayBuffer(), { status: r.status, headers });
}

async function safeUpstreamFetch(doFetch: () => Promise<Response>) {
  const maxAttempts = 3;
  for (let i = 0; i < maxAttempts; i++) {
    try {
      const r = await doFetch();
      return await forwardResponse(r);
    } catch (e: any) {
      const code = e?.cause?.code || e?.code;
      const retryable = code === "ECONNREFUSED" || code === "ENOTFOUND" || code === "EAI_AGAIN";
      if (!retryable || i === maxAttempts - 1) {
        return new Response(
          JSON.stringify({
            detail: "上游后端不可达（backend 容器可能正在重启或未就绪）。",
            error: String(code || e?.message || e)
          }),
          { status: 503, headers: { "content-type": "application/json; charset=utf-8" } }
        );
      }
      await new Promise((r) => setTimeout(r, 200 * (i + 1)));
    }
  }
  return new Response(JSON.stringify({ detail: "unknown" }), { status: 503 });
}