export async function GET() {
    const encoder = new TextEncoder();
    const stream = new ReadableStream({
        start(controller) {
            let closed = false;
            emitter.incrementTargets?.();
            let keepAlive;
            const cleanup = () => {
                if (!closed) {
                    closed = true;
                    clearInterval(keepAlive);
                    emitter.off('event', listener);
                    emitter.decrementTargets?.();
                    try {
                        controller.close();
                    } catch {
                        // ignore if the controller is already closed
                    }
                }
            };

            const send = (data) => {
                if (closed) return;
                try {
                    controller.enqueue(encoder.encode(`data: ${JSON.stringify(data)}\n\n`));
                } catch {
                    cleanup();
                }
            };

            const listener = (event) => send(event);
            emitter.on('event', listener);

            for (const queued of emitter.getQueue?.() || []) {
                send(queued);
            }

            keepAlive = setInterval(() => {
                try {
                    controller.enqueue(encoder.encode(':\n\n'));
                } catch {
                    cleanup();
                }
            }, 15_000);

            controller.signal?.addEventListener('abort', cleanup);
        },
        cancel() {
            this.onClose?.();
        }
    });

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