/**
 * The tab's title: the page's, the site's name, and an unread badge.
 *
 * @module
 */

import { useEffect } from "react";

/**
 * Returns the site's name. The server injects the configured site name into
 * both <title> and a `site-name` meta tag (see api/lib/static.ts /
 * api/middleware/og.ts). In the Vite dev server the placeholder isn't
 * substituted, so it falls back to "gerbeur".
 */
function readSiteName(): string {
  const meta = document.querySelector('meta[name="site-name"]')
    ?.getAttribute("content")?.trim();
  if (meta && meta !== "__SITE_NAME__") return meta;
  return "gerbeur";
}

/** The site's name, read once at startup. */
export const SITE_NAME: string = readSiteName();

/**
 * Returns the site's emoji. The server injects the configured emoji into a
 * `site-emoji` meta tag; it falls back to the default truck.
 */
function readSiteEmoji(): string {
  const meta = document.querySelector('meta[name="site-emoji"]')
    ?.getAttribute("content")?.trim();
  if (meta && meta !== "__SITE_EMOJI__") return meta;
  return "🚚";
}

/** The site's emoji, read once at startup. */
export const SITE_EMOJI: string = readSiteEmoji();

/**
 * The page's title and the site's name. The page title and the unread badge are
 * set from different places (each page, and the live-updates provider), so both
 * are kept here and composed. `null` means no page has set one yet: keep the
 * server-rendered title.
 */
let baseTitle: string | null = null;
/** The unread count. */
let badge = 0;

/** Sets the tab's title from {@link baseTitle} and {@link badge}. */
function applyTitle() {
  const base = baseTitle ?? document.title.replace(/^\(\d+\+?\) /, "");
  document.title = badge > 0 ? `(${badge > 99 ? "99+" : badge}) ${base}` : base;
}

/**
 * Keeps document.title in sync with the current page during client-side
 * navigation. Without this the tab title only ever reflects the server-rendered
 * <title> from the initial page load and goes stale on every SPA navigation.
 *
 * - Pass a non-empty `title` to show `<title> · <site name>`.
 * - Pass `null` to show just the site name (home / generic pages).
 * - Pass `undefined` while the page-specific title is still loading: the title
 * is left untouched, so a server-rendered OG title survives until data
 * arrives (avoids a flash to the bare site name on direct loads).
 */
export function useDocumentTitle(title: string | null | undefined): void {
  useEffect(() => {
    if (title === undefined) return;
    baseTitle = title ? `${title} · ${SITE_NAME}` : SITE_NAME;
    applyTitle();
  }, [title]);
}

/**
 * Prefixes the tab title with the unread `count`, e.g. "(3) Chat · gerbeur".
 */
export function setTitleBadge(count: number): void {
  if (count === badge) return;
  badge = count;
  applyTitle();
}