/* ============================================================================
   EVENT -> iCALENDAR  (resource route)
   ----------------------------------------------------------------------------
   /{locale}/events-calendar/{slug}.ics

   This module exports a `loader` and nothing else - no component, no
   ErrorBoundary - which is what makes React Router treat it as a resource
   route and hand the loader's Response straight to the browser.

   Because a resource route is served on its own, the ":lang" layout above it
   does NOT run: its loader is not called for this request, so the locale
   segment is validated here as well. `requireLocale` throws the same 404 the
   layout would have.

   The file itself is built by ./_events-opportunities/ics.ts, which follows
   RFC 5545 rather than one client's tolerance - CRLF endings, 75-octet folding
   on character boundaries (an Arabic title is two bytes per letter), escaped
   TEXT values and an exclusive DTEND for an all-day event.
   ========================================================================= */

import { redirect } from "react-router";

import { isLocale, sectionPath, translate } from "~/i18n";
import { getSiteUrl } from "~/lib/env.server";
import { canonicalUrl } from "~/lib/seo";
import { requireEntity } from "~/lib/strapi";

import type { Route } from "./+types/events-calendar.$slug.ics";
import { getRouteCopy } from "./_events-opportunities/copy";
import { fetchEvent } from "./_events-opportunities/events.server";
import { buildIcsCalendar, icsResponse } from "./_events-opportunities/ics";
import { requireLocale } from "./_shared/listing";

/** Only used to name the file; the CMS slug supplies the rest. */
const FILENAME_PREFIX = "sharp-er";

export async function loader({ params, request }: Route.LoaderArgs) {
  /* The ":lang" layout normally 301s "/EN/..." to "/en/...", but its loader
     does not run for a resource route, so the same normalisation happens here
     rather than answering a 404 for a URL the rest of the site accepts. */
  const segment = params.lang;
  const normalized = segment?.toLowerCase();
  if (segment && normalized !== segment && isLocale(normalized)) {
    const url = new URL(request.url);
    throw redirect(
      `${url.pathname.replace(/^\/[^/]+/, `/${normalized}`)}${url.search}`,
      301,
    );
  }

  const locale = requireLocale(normalized);
  const slug = params.slug ?? "";

  const { event } = requireEntity(await fetchEvent(slug, locale));

  const siteUrl = getSiteUrl(request);
  const pathname = `${sectionPath("events", locale)}/${encodeURIComponent(slug)}`;
  const url = canonicalUrl(siteUrl, pathname);
  const copy = getRouteCopy(locale);

  const location =
    event.place ??
    (event.format === "online" ? translate(locale, "events.online") : undefined);

  /* The joining link belongs in the calendar entry, not only on the page: by
     the time the reminder fires, the page is not what is in front of anyone. */
  const description = [
    event.summary,
    event.onlineUrl
      ? `${copy.eventDetail.joinOnlineLabel}: ${event.onlineUrl}`
      : undefined,
    url,
  ]
    .filter(Boolean)
    .join("\n\n");

  const calendar = buildIcsCalendar(
    [
      {
        /* documentId is shared by an entry's translations in Strapi 5, so the
           locale is part of the UID - importing the Arabic file must not
           overwrite the English entry already in someone's calendar. */
        uid: `${event.documentId}.${locale}@sharper.ly`,
        start: event.start,
        // Only an explicit end is written: inventing a duration would put a
        // wrong-length block in a reader's calendar.
        end: event.end,
        allDay: event.allDay,
        summary: event.title,
        description,
        location,
        url,
        status: "CONFIRMED",
      },
    ],
    { name: translate(locale, "nav.sections.events") },
  );

  return icsResponse(calendar, `${FILENAME_PREFIX}-${slug}.ics`);
}