// ISS-129 (v0.57.0): in-process fan-out registry for the SSE state stream (/api/events). The app
// runs as one long-lived server process (`next start`; instrumentation.ts already keeps background
// sim state alive) — no new dependencies, no WS upgrade needed. The Set lives on globalThis because
// Next.js gives instrumentation.ts (where broadcast() fires from the background tick) and route
// handlers (where subscribe() happens in /api/events) separate module instances; a plain `let` would
// give each its own empty set and no push would ever be delivered.

type Push = (text: string) => void;

const g = globalThis as unknown as { __flightSseSubscribers?: Set<Push> };
const subscribers: Set<Push> = (g.__flightSseSubscribers ??= new Set());

export function subscribe(fn: Push): () => void {
  subscribers.add(fn);
  return () => {
    subscribers.delete(fn);
  };
}

// Call each subscriber safely — one dead stream must not take the others down.
export function broadcast(text: string): void {
  for (const fn of [...subscribers]) {
    try {
      fn(text);
    } catch {
      // subscriber's stream is gone; its own cleanup unsubscribes it
    }
  }
}