/**
 * Server request shell. Reads the incoming request once and does two things,
 * both decided by pure functions in src/domain:
 *
 * 1. Picks the language of the request and maps the public address onto the
 *    app directory (routes.ts).
 * 2. Records a page view server-side (pageview-decision.ts). No tracking
 *    script ships to the browser.
 *
 * Page views are browser navigations (`sec-fetch-dest: document`).
 * Router-internal headers (RSC, next-router-prefetch) are stripped by the
 * server before this shell runs and cannot be used here.
 */

import { NextResponse, type NextRequest } from "next/server";

import { recordPageviewToUmami } from "@/src/analytics/recordPageviewToUmami";
import { LOCALE_COOKIE } from "@/src/domain/locale";
import { decidePageview } from "@/src/domain/pageview-decision";
import { routeRequest } from "@/src/domain/routes";

const PERMANENT = 308;
const TEMPORARY = 307;

const primaryLanguage = (acceptLanguage: string | null): string =>
  acceptLanguage?.split(",")[0]?.split(";")[0]?.trim() ?? "";

const firstForwardedIp = (forwardedFor: string | null): string =>
  forwardedFor?.split(",")[0]?.trim() ?? "";

const hostnameWithoutPort = (host: string): string => host.replace(/:\d+$/, "");

export function proxy(request: NextRequest): NextResponse {
  const route = routeRequest({
    pathname: request.nextUrl.pathname,
    cookie: request.cookies.get(LOCALE_COOKIE)?.value,
    acceptLanguage: request.headers.get("accept-language"),
  });

  const url = request.nextUrl.clone();
  url.pathname = route.to;
  const response =
    route.kind === "redirect"
      ? NextResponse.redirect(url, route.permanent ? PERMANENT : TEMPORARY)
      : NextResponse.rewrite(url);

  // The answer depends on the visitor's language: caches must keep one per language.
  if (route.negotiated) {
    response.headers.append("Vary", "Accept-Language, Cookie");
  }

  // A redirect is not a view: the request that follows it is counted instead.
  if (route.kind !== "redirect") {
    const pageview = decidePageview({
      method: request.method,
      secFetchDest: request.headers.get("sec-fetch-dest") ?? "",
      // The public address the visitor asked for, not the internal one it maps to.
      pathname: request.nextUrl.pathname,
      search: request.nextUrl.search,
      hostname: hostnameWithoutPort(
        request.headers.get("x-forwarded-host") ??
          request.headers.get("host") ??
          "",
      ),
      referrer: request.headers.get("referer") ?? "",
      language: primaryLanguage(request.headers.get("accept-language")),
      userAgent: request.headers.get("user-agent") ?? "",
      clientIp: firstForwardedIp(request.headers.get("x-forwarded-for")),
    });
    if (pageview.track) {
      recordPageviewToUmami(pageview.facts);
    }
  }

  return response;
}

export const config = {
  // Pages only: not Next's own files, the error proxy, or files.
  matcher: ["/((?!_next/|errors/|.*\\..*).*)"],
};