// Repackage the static Vite/TanStack-Start build (.output/public) into the Vercel
// Build Output API layout (.vercel/output), generating the /dashboard/api/* proxy
// destination from a per-project env var.
//
// Why this exists: prod deploys via a fast-forward-only promotion, so the `dev` and
// `main` branches are byte-identical and a committed vercel.json CANNOT differ between
// them. The app is same-origin only (no backend CORS), so the per-environment backend
// must be the PROXY DESTINATION, supplied per Vercel project as LANGGRAPH_BACKEND_URL.
// Vercel reads vercel.json BEFORE the build and never interpolates env into it, so the
// routes are emitted here (read AFTER the build) where process.env is available.
import { cp, mkdir, writeFile, rm } from "node:fs/promises"

const backend = process.env.LANGGRAPH_BACKEND_URL
if (!backend) {
  throw new Error(
    "LANGGRAPH_BACKEND_URL is required at build time (set it per Vercel project: " +
      "dev project -> dev langgraph URL, prod project -> prod langgraph URL).",
  )
}
const base = backend.replace(/\/$/, "")

await rm(".vercel/output", { recursive: true, force: true })
await mkdir(".vercel/output/static", { recursive: true })
await cp(".output/public", ".vercel/output/static", { recursive: true })

await writeFile(
  ".vercel/output/config.json",
  JSON.stringify(
    {
      version: 3,
      routes: [
        // Same-origin proxy to this project's backend (proxy, not redirect, so the
        // osw_session cookie stays first-party on the Vercel origin).
        { src: "^/dashboard/api/(.*)$", dest: `${base}/dashboard/api/$1` },
        // Serve hashed assets, the PWA manifest/service worker, and _shell.html itself
        // BEFORE the SPA catch-all, or static files get swallowed by the fallback.
        { handle: "filesystem" },
        // SPA fallback (replaces the old vercel.json /(.*) -> /_shell.html rewrite).
        { src: "^/.*$", dest: "/_shell.html" },
      ],
    },
    null,
    2,
  ) + "\n",
)

console.log(`[build-vercel-output] wrote .vercel/output/config.json (backend: ${base})`)