import { EventEmitter } from "node:events";
import type { CanonicalQuote, ConnectorHealth, MarketEvent, Observation, RawObservation } from "@market-atlas/market-model";

/**
 * Internal market bus. In-process today (modular monolith); the topic names mirror the
 * spec so that a NATS/Redpanda transport can replace this class without touching producers.
 */
export interface BusTopics {
  "raw.observation": RawObservation;
  "normalized.observation": Observation;
  "canonical.quote": CanonicalQuote;
  "market.event": MarketEvent;
  "connector.health": ConnectorHealth;
  "market.state": { exchangeId: string; state: string; at: number };
}

type Handler<T> = (msg: T) => void;

export class MarketBus {
  private emitter = new EventEmitter({ captureRejections: false });
  readonly counters: Record<string, number> = {};

  constructor() {
    this.emitter.setMaxListeners(200);
  }

  publish<K extends keyof BusTopics>(topic: K, msg: BusTopics[K]): void {
    this.counters[topic] = (this.counters[topic] ?? 0) + 1;
    this.emitter.emit(topic, msg);
  }

  subscribe<K extends keyof BusTopics>(topic: K, handler: Handler<BusTopics[K]>): () => void {
    this.emitter.on(topic, handler);
    return () => this.emitter.off(topic, handler);
  }
}

export const bus = new MarketBus();