const WHISPER_URL = process.env.WHISPER_URL ?? 'http://localhost:8080';

/** Relay the whisper /model/events SSE stream to the browser. */
export async function GET({ request }) {
	const { default: fetch } = await import('node-fetch');

	const ac = new AbortController();
	request.signal.addEventListener('abort', () => ac.abort());

	const stream = new ReadableStream({
		async start(controller) {
			try {
				const upstream = await fetch(`${WHISPER_URL}/model/events`, {
					signal: ac.signal as AbortSignal
				});
				if (!upstream.body) {
					controller.close();
					return;
				}
				for await (const chunk of upstream.body) {
					if (ac.signal.aborted) break;
					controller.enqueue(chunk instanceof Buffer ? chunk : Buffer.from(String(chunk)));
				}
			} catch {
				// upstream closed, client disconnected, or whisper unreachable — all fine
			} finally {
				controller.close();
			}
		},
		cancel() {
			ac.abort();
		}
	});

	return new Response(stream, {
		headers: {
			'Content-Type': 'text/event-stream',
			'Cache-Control': 'no-cache',
			Connection: 'keep-alive',
			'X-Accel-Buffering': 'no'
		}
	});
}