agentic-dev/packages/core-events/src/in-memory-event-bus.ts

import type { z } from "zod";
import type { EventDescriptor } from "./event-descriptor";
import type { EventHandler, IEventBus } from "./event-bus.interface";

export type InMemoryEventBusOptions = {
  /** When true, rethrow the first handler error (default: false — errors swallowed). */
  failFast?: boolean;
};

export class InMemoryEventBus implements IEventBus {
  private readonly handlers = new Map<string, EventHandler<unknown>[]>();

  constructor(private readonly options: InMemoryEventBusOptions = {}) {}

  async publish<T>(
    descriptor: EventDescriptor<string, z.ZodType<T>>,
    payload: T,
  ): Promise<void> {
    descriptor.schema.parse(payload);
    const subscribers = this.handlers.get(descriptor.name) ?? [];
    if (subscribers.length === 0) return;
    const settled = await Promise.allSettled(
      subscribers.map((h) => h(payload)),
    );
    if (this.options.failFast) {
      const failure = settled.find((s) => s.status === "rejected");
      // Only the first rejection is rethrown. Other failures are intentionally
      // dropped — `failFast` is a test-affordance, not a fault-tolerance design.
      if (failure && failure.status === "rejected") throw failure.reason;
    }
  }

  subscribe<T>(
    descriptor: EventDescriptor<string, z.ZodType<T>>,
    _consumerFeature: string,
    handler: EventHandler<T>,
  ): void {
    const arr = this.handlers.get(descriptor.name) ?? [];
    arr.push(handler as EventHandler<unknown>);
    this.handlers.set(descriptor.name, arr);
  }
}