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",
			}
		}
	);
}