import type { ServerResponse } from 'node:http';

type EventPayload = unknown;

type EventListener = (payload: EventPayload) => void;

export class HostEventBus {
  private readonly listeners = new Map<string, Set<EventListener>>();
  private readonly sseClients = new Set<ServerResponse>();

  on(eventName: string, listener: EventListener): () => void {
    const bucket = this.listeners.get(eventName) ?? new Set<EventListener>();
    bucket.add(listener);
    this.listeners.set(eventName, bucket);

    return () => {
      bucket.delete(listener);
      if (bucket.size === 0) {
        this.listeners.delete(eventName);
      }
    };
  }

  addSseClient(res: ServerResponse): void {
    this.sseClients.add(res);
    res.on('close', () => {
      this.sseClients.delete(res);
    });
  }

  emit(eventName: string, payload: EventPayload): void {
    const bucket = this.listeners.get(eventName);
    if (bucket) {
      for (const listener of bucket) {
        listener(payload);
      }
    }

    if (this.sseClients.size > 0) {
      const message = `event: ${eventName}\ndata: ${JSON.stringify(payload)}\n\n`;
      for (const client of this.sseClients) {
        try {
          client.write(message);
        } catch {
          this.sseClients.delete(client);
        }
      }
    }
  }

  closeAll(): void {
    this.listeners.clear();
    for (const client of this.sseClients) {
      try {
        client.end();
      } catch {
        // Ignore individual client close failures.
      }
    }
    this.sseClients.clear();
  }
}

export const hostEventBus = new HostEventBus();