/**

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

 *

 * @flow

 */

export default class EventEmitter<Events: Object> {

  listenersMap: Map<string, Array<Function>> = new Map();

  addListener<Event: $Keys<Events>>(

    event: Event,

    listener: (...$ElementType<Events, Event>) => any,

  ): void {

    const listeners = this.listenersMap.get(event);

    if (listeners === undefined) {

      this.listenersMap.set(event, [listener]);

    } else {

      const index = listeners.indexOf(listener);

      if (index < 0) {

        listeners.push(listener);

      }

    }

  }

  emit<Event: $Keys<Events>>(

    event: Event,

    ...args: $ElementType<Events, Event>

  ): void {

    const listeners = this.listenersMap.get(event);

    if (listeners !== undefined) {

      if (listeners.length === 1) {

        // No need to clone or try/catch

        const listener = listeners[0];

        listener.apply(null, args);

      } else {

        let didThrow = false;

        let caughtError = null;

        const clonedListeners = Array.from(listeners);

        for (let i = 0; i < clonedListeners.length; i++) {

          const listener = clonedListeners[i];

          try {

            listener.apply(null, args);

          } catch (error) {

            if (caughtError === null) {

              didThrow = true;

              caughtError = error;

            }

          }

        }

        if (didThrow) {

          throw caughtError;

        }

      }

    }

  }

  removeAllListeners(): void {

    this.listenersMap.clear();

  }

  removeListener(event: $Keys<Events>, listener: Function): void {

    const listeners = this.listenersMap.get(event);

    if (listeners !== undefined) {

      const index = listeners.indexOf(listener);

      if (index >= 0) {

        listeners.splice(index, 1);

      }

    }

  }

}