import { observationReader } from '$lib/server/fleet/status.js';
import { listServers } from '$lib/server/fleet/servers.js';
import { statusEntry } from '$lib/server/pipeline/worker.js';
import { subscribe } from '$lib/server/pipeline/bus.js';
import { listTelemetry } from '$lib/server/fleet/telemetry.js';

const encoder = new TextEncoder();
const HEARTBEAT_MS = 20_000;

export async function GET() {
    let heartbeat: NodeJS.Timeout | null = null;
    let unsubscribe: (() => void) | null = null;

    const stream = new ReadableStream<Uint8Array>({
        start(controller) {
            unsubscribe = subscribe((event) => {
                if (event.type === 'server-status' || event.type === 'server-telemetry') {
                    controller.enqueue(encoder.encode(`event: ${event.type}\ndata: ${JSON.stringify({ ...event, serverNow: Date.now() })}\n\n`));
                }
            });
            const observation = observationReader();
            const observe = (server: ReturnType<typeof listServers>[number]) => statusEntry(server, observation);
            controller.enqueue(encoder.encode(': hello\n\n'));
            controller.enqueue(encoder.encode(`event: server-status\ndata: ${JSON.stringify({ entries: listServers().map(server => observe(server)), snapshot: true, serverNow: Date.now() })}\n\n`));
            controller.enqueue(encoder.encode(`event: server-telemetry\ndata: ${JSON.stringify({ entries: listTelemetry(), snapshot: true, serverNow: Date.now() })}\n\n`));
            heartbeat = setInterval(() => controller.enqueue(encoder.encode(': ping\n\n')), HEARTBEAT_MS);
        },
        cancel() {
            if (heartbeat) clearInterval(heartbeat);
            if (unsubscribe) unsubscribe();
        }
    });

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