Implement EventStream for live schedule updates

app/api/events/route.ts

@@ -0,0 +1,69 @@
+import { Schedule } from "@/app/schedule/types";
+
+function sendMessage(
+	stream: WritableStream<string>,
+	message: string,
+) {
+	const writer = stream.getWriter();
+	writer.ready
+		.then(() => writer.write(message))
+		.catch(console.error)
+		.finally(() => writer.releaseLock())
+	;
+}
+
+let streams = new Set<WritableStream<string>>();
+let lastBroadcastData: string | null = null;
+let lastBroadcastId = 0;
+export function broadcastUpdate(schedule: Schedule) {
+	const id = Date.now();
+	const data = JSON.stringify(schedule);
+	lastBroadcastId = id;
+	lastBroadcastData = data;
+	const message = `id: ${id}\nevent: update\ndata: ${data}\n\n`
+	for (const stream of streams) {
+		sendMessage(stream, message);
+	}
+}
+
+setInterval(() => {
+	for (const stream of streams) {
+		sendMessage(stream, "data: keepalive\n\n");
+	}
+}, 10e3)
+
+export async function GET(request: Request) {
+	const encoder = new TextEncoder();
+	const source = request.headers.get("x-forwarded-for");
+	console.log(`starting event stream for ${source}`)
+	const stream = new TransformStream<string, Uint8Array>({
+		transform(chunk, controller) {
+			controller.enqueue(encoder.encode(chunk));
+		},
+		flush(controller) {
+			console.log(`finished event stream for ${source}`);
+			streams.delete(stream.writable);
+		},
+		// @ts-expect-error experimental API
+		cancel(reason) {
+			console.log(`cancelled event stream for ${source}`);
+			streams.delete(stream.writable);
+		}
+	})
+	streams.add(stream.writable);
+	if (lastBroadcastId) {
+		sendMessage(
+			stream.writable,
+			`id: ${lastBroadcastData}\nevent: update\ndata: ${lastBroadcastData}\n\n`
+		);
+	}
+	return new Response(
+		stream.readable,
+		{
+			headers: {
+				"Access-Control-Allow-Origin": "*",
+				"Content-Type": "text/event-stream",
+			}
+		}
+	);
+}

app/schedule/context.tsx

@@ -0,0 +1,41 @@
+"use client";
+import { createContext, useContext, useEffect, useState } from "react";
+import { Schedule } from "./types";
+
+const ScheduleContext = createContext<Schedule | null>(null);
+
+interface ScheduleProviderProps {
+	children: React.ReactElement;
+	schedule: Schedule;
+}
+
+export function ScheduleProvider(props: ScheduleProviderProps) {
+	const [schedule, setSchedule] = useState(props.schedule);
+	useEffect(() => {
+		console.log("Opening event source")
+		const source = new EventSource("/api/events");
+		source.addEventListener("message", (message) => {
+			console.log("Message", message.data);
+			setSchedule(old => {
+				const copy: Schedule = JSON.parse(JSON.stringify(old));
+				const ts = copy.events[0].slots[0].start;
+				copy.events[0].slots[0].start = new Date(Date.parse(ts) + 36e5).toISOString();
+				return copy;
+			})
+		});
+		source.addEventListener("update", (message) => console.log("Update", message.data));
+		return () => {
+			console.log("Closing event source")
+			source.close();
+		}
+	}, [])
+	return (
+		<ScheduleContext.Provider value={schedule}>
+			{props.children}
+		</ScheduleContext.Provider>
+	);
+}
+
+export function useSchedule() {
+	return useContext(ScheduleContext);
+}

app/schedule/page.tsx

@@ -1,38 +1,26 @@
 import Timetable from "@/ui/timetable"
-import styles from "./page.module.css"
-import { Schedule, ScheduleEvent } from "./types"
+import { Schedule } from "./types"
 import { readFile } from "fs/promises"
+import { ScheduleProvider } from "./context"
+import { Events } from "@/ui/events";
+import { Locations } from "@/ui/locations";
 
-function EventInfo(props: { event: ScheduleEvent }) {
-	return <section className={styles.event}>
-		<h3>{props.event.name}</h3>
-		<p>{props.event.description ?? "No description provided"}</p>
-		<h4>Timeslots</h4>
-		<ul>
-			{props.event.slots.map(slot => <li key={slot.id}>
-				{slot.start} - {slot.end}
-			</li>)}
-		</ul>
-	</section>
-}
-
-export default async function schedule() {
+export default async function page() {
 	const schedule: Schedule = JSON.parse(await readFile("schedule.json", "utf-8"));
-	return <main className={styles.schedule}>
-		<h1>Schedule & Events</h1>
-		<p>
-			Study carefully, we only hold these events once a year.
-		</p>
-		<h2>Schedule</h2>
-		<Timetable schedule={schedule} />
-		<h2>Events</h2>
-		{schedule.events.map(event => <EventInfo event={event} key={event.id}/>)}
-		<h2>Locations</h2>
-		<ul>
-			{schedule.locations.map(location => <li key={location.id}>
-				<h3>{location.name}</h3>
-				{location.description ?? "No description provided"}
-			</li>)}
-		</ul>
-	</main>
+	return (
+		<ScheduleProvider schedule={schedule}>
+			<main>
+				<h1>Schedule & Events</h1>
+				<p>
+					Study carefully, we only hold these events once a year.
+				</p>
+				<h2>Schedule</h2>
+				<Timetable />
+				<h2>Events</h2>
+				<Events />
+				<h2>Locations</h2>
+				<Locations />
+			</main>
+		</ScheduleProvider>
+	);
 }

ui/events.tsx

@@ -0,0 +1,24 @@
+"use client";
+import styles from "./events.module.css"
+import { useSchedule } from "@/app/schedule/context";
+import { ScheduleEvent } from "@/app/schedule/types";
+
+function EventInfo(props: { event: ScheduleEvent }) {
+	return <section className={styles.event}>
+		<h3>{props.event.name}</h3>
+		<p>{props.event.description ?? "No description provided"}</p>
+		<h4>Timeslots</h4>
+		<ul>
+			{props.event.slots.map(slot => <li key={slot.id}>
+				{slot.start} - {slot.end}
+			</li>)}
+		</ul>
+	</section>
+}
+
+export function Events() {
+	const schedule = useSchedule();
+	return <>
+		{schedule!.events.map(event => <EventInfo event={event} key={event.id}/>)}
+	</>;
+}

ui/locations.tsx

@@ -0,0 +1,12 @@
+"use client";
+import { useSchedule } from "@/app/schedule/context";
+
+export function Locations() {
+	const schedule = useSchedule();
+	return <ul>
+		{schedule!.locations.map(location => <li key={location.id}>
+			<h3>{location.name}</h3>
+			{location.description ?? "No description provided"}
+		</li>)}
+	</ul>;
+}

ui/timetable.tsx

@@ -1,5 +1,7 @@
-import { Schedule, ScheduleEvent, ScheduleLocation, TimeSlot } from "@/app/schedule/types";
+"use client";
+import { ScheduleEvent, ScheduleLocation, TimeSlot } from "@/app/schedule/types";
 import styles from "./timetable.module.css";
+import { useSchedule } from "@/app/schedule/context";
 
 const oneDayMs = 24 * 60 * 60 * 1000;
 const oneHourMs = 60 * 60 * 1000;
@@ -318,8 +320,8 @@ function tableElementsFromStretches(
 	};
 }
 
-export default function Timetable(props: { schedule: Schedule }) {
-	const { locations, events } = props.schedule;
+export default function Timetable() {
+	const { locations, events } = useSchedule()!;
 	const junctions = junctionsFromEdges(edgesFromEvents(events));
 	const stretches = [...stretchesFromSpans(spansFromJunctions(junctions, locations), oneHourMs * 5)];
 	const {