/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 * @format
 */
'use strict';

import EventEmitter from './_EventEmitter';
import type { EventSubscription } from './EventSubscription';
export default EventEmitter;
export type { EventSubscription };
/**
 * Essential interface for an EventEmitter.
 */

export interface IEventEmitter<TEventToArgsMap: {...}> {
  /**
   * Registers a listener that is called when the supplied event is emitted.
   * Returns a subscription that has a `remove` method to undo registration.
   */
  addListener<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent, listener: (...args: $ElementType<TEventToArgsMap, TEvent>) => mixed, context?: mixed): EventSubscription,

  /**
   * Emits the supplied event. Additional arguments supplied to `emit` will be
   * passed through to each of the registered listeners.
   */
  emit<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent, ...args: $ElementType<TEventToArgsMap, TEvent>): void,

  /**
   * Removes all registered listeners.
   */
  removeAllListeners<TEvent: $Keys<TEventToArgsMap>>(eventType?: ?TEvent): void,

  /**
   * Returns the number of registered listeners for the supplied event.
   */
  listenerCount<TEvent: $Keys<TEventToArgsMap>>(eventType: TEvent): number,
}