import type { SyncDBEventName, SyncDBEventHandler } from './types.js';

export class Emitter {
  private listeners = new Map<SyncDBEventName, Set<SyncDBEventHandler>>();

  on(event: SyncDBEventName, handler: SyncDBEventHandler): () => void {
    let set = this.listeners.get(event);
    if (!set) {
      set = new Set();
      this.listeners.set(event, set);
    }
    set.add(handler);
    return () => {
      set!.delete(handler);
    };
  }

  emit(event: SyncDBEventName, ...args: unknown[]): void {
    const set = this.listeners.get(event);
    if (!set) return;
    for (const fn of set) {
      try {
        fn(...args);
      } catch {
        // listener errors must not break the library
      }
    }
  }

  removeAll(): void {
    this.listeners.clear();
  }
}