waving-hands/src/lib/components/Announcement.svelte

<script lang="ts">
	// The site-family announcement, shown by every game: the maintainer writes
	// /var/lib/hall/announcement.json on the host (hall-announce), and each game's
	// site serves it at /hall/announcement.json. It is fetched on load, every few
	// minutes, and whenever the tab becomes visible again. Dismissal is per
	// announcement id, so the next one still shows.
	import { onMount } from 'svelte';

	interface Announcement {
		/** Names this announcement, so dismissing it does not hide the next. */
		id: string;
		text: string;
		/** When what it announces happens, told in each reader's own time. */
		at?: string;
		/** After this it is no longer shown. */
		until?: string;
	}

	const SOURCE = '/hall/announcement.json';
	const CHECK_MS = 5 * 60_000;
	const DISMISSED = 'hall:dismissed';

	let current = $state<Announcement | null>(null);
	let dismissed = $state<string | null>(null);
	let now = $state(Date.now());

	async function check() {
		try {
			const res = await fetch(SOURCE, { cache: 'no-store' });
			const a: unknown = res.ok ? await res.json() : null;
			current = a && typeof a === 'object' && typeof (a as Announcement).text === 'string' && (a as Announcement).text && typeof (a as Announcement).id === 'string' ? (a as Announcement) : null;
		} catch {
			// No announcement reachable: none shown.
		}
		now = Date.now();
	}

	onMount(() => {
		try {
			dismissed = localStorage.getItem(DISMISSED);
		} catch {
			// Without storage a dismissal lasts this visit.
		}
		void check();
		const poll = setInterval(check, CHECK_MS);
		const tick = setInterval(() => (now = Date.now()), 30_000);
		const looked = () => {
			if (document.visibilityState === 'visible') void check();
		};
		document.addEventListener('visibilitychange', looked);
		return () => {
			clearInterval(poll);
			clearInterval(tick);
			document.removeEventListener('visibilitychange', looked);
		};
	});

	const shown = $derived(current && current.id !== dismissed && !(current.until && Date.parse(current.until) < now) ? current : null);

	/** When it happens, in the reader's own clock: "in 25 minutes, at 7:00 AM", or the day and time further off. */
	const when = $derived.by(() => {
		const t = shown?.at ? Date.parse(shown.at) : NaN;
		if (!Number.isFinite(t)) return '';
		const minutes = Math.round((t - now) / 60_000);
		if (minutes > 90) return ` (${new Date(t).toLocaleString([], { weekday: 'short', hour: 'numeric', minute: '2-digit' })}, your time)`;
		if (minutes > 1) return ` (in ${minutes} minutes, at ${new Date(t).toLocaleTimeString([], { hour: 'numeric', minute: '2-digit' })})`;
		return minutes >= -15 ? ' (now)' : '';
	});

	function dismiss() {
		// Taken first: once dismissed, nothing is shown.
		const id = shown?.id;
		if (!id) return;
		dismissed = id;
		try {
			localStorage.setItem(DISMISSED, id);
		} catch {
			// The dismissal still holds for this visit.
		}
	}
</script>

{#if shown}
	<div class="hall-announcement" role="status">
		<span>{shown.text}{when}</span>
		<button type="button" aria-label="Dismiss this announcement" onclick={dismiss}>×</button>
	</div>
{/if}

<style>
	/* Fixed colours rather than the game's tokens, so the notice looks the same on every site that shows it. */
	.hall-announcement {
		position: sticky;
		top: 0;
		z-index: 1000;
		display: flex;
		align-items: center;
		justify-content: center;
		gap: 0.8rem;
		padding: 0.45rem 2.4rem 0.45rem 1rem;
		background: #f2c45a;
		color: #1d1a12;
		font: 500 0.95rem/1.35 system-ui, -apple-system, 'Segoe UI', sans-serif;
		text-align: center;
		box-shadow: 0 1px 4px #0005;
	}

	button {
		position: absolute;
		right: 0.5rem;
		background: none;
		border: 0;
		color: inherit;
		font-size: 1.3rem;
		line-height: 1;
		padding: 0.2rem 0.5rem;
		cursor: pointer;
	}
</style>