import { existsSync } from "node:fs";
import { dirname, resolve } from "node:path";
import { fileURLToPath } from "node:url";
import fastifyStatic from "@fastify/static";
import type { FastifyInstance } from "fastify";

// Serve the built React SPA (apps/web/dist) from the Fastify server, so ONE container
// serves both the API and the operator UI — matching the offline-first single-appliance
// model (the booth has no separate web host). This is a NO-OP in dev (the Vite dev server
// serves the SPA on its own port and no dist exists), so it never changes local behavior.
//
// Registration order matters: this is registered LAST, after every API route, and its
// catch-all is GET-only and explicitly excludes /api, /health, and the WS path — so it
// can never shadow the backend. See wiki/decisions/container-deployment.md.

/** Where the built SPA lives. Override with WEB_DIST_DIR (the container sets it). Default
 *  resolves relative to this file's dist location: apps/server/dist → ../../web/dist, the
 *  layout the image lays down (/app/dist + /app/web/dist → ../web/dist from dist). */
function resolveWebDist(): string {
  const fromEnv = process.env.WEB_DIST_DIR;
  if (fromEnv) return resolve(fromEnv);
  const here = dirname(fileURLToPath(import.meta.url));
  // In the image the server runs from /app/dist and the SPA sits at /app/web/dist.
  return resolve(here, "../web/dist");
}

/**
 * Register SPA static serving if a build is present. Returns true when wired, false when
 * skipped (dev / no build). Serves assets from the dist dir and falls back to index.html
 * for any non-API GET so client-side routing (TanStack Router) works on deep links/reload.
 */
export async function registerSpa(app: FastifyInstance): Promise<boolean> {
  const root = resolveWebDist();
  const indexHtml = resolve(root, "index.html");
  if (!existsSync(indexHtml)) {
    app.log.info(`SPA static serving disabled (no build at ${root})`);
    return false;
  }

  await app.register(fastifyStatic, { root, wildcard: false });

  // SPA fallback: any GET that didn't match an API route or a real static file returns
  // index.html (client routing). EXCLUDE the backend surfaces so a missing /api route
  // still 404s as JSON rather than silently returning the HTML shell. WS upgrades and
  // non-GET methods are never touched (this is a GET-only notFound handler path).
  app.setNotFoundHandler((req, reply) => {
    const url = req.raw.url ?? "/";
    if (req.method !== "GET" || url.startsWith("/api") || url.startsWith("/health")) {
      return reply.code(404).send({ error: "not found" });
    }
    return reply.sendFile("index.html");
  });

  app.log.info(`SPA static serving enabled from ${root}`);
  return true;
}