import { EventEmitter } from "events";

/**
 * Generic observable.
 * @public
 */
export interface Emitter<T> {
  /**
   * Sets up a function that will be called whenever the target changes.
   * @param listener - Callback function.
   * @param options - An options object that specifies characteristics about the listener.
   *                  If once true, indicates that the listener should be invoked at most once after being added.
   *                  If once true, the listener would be automatically removed when invoked.
   */
  addListener(listener: (data: T) => void, options?: { once?: boolean }): void;
  /**
   * Removes from the listener previously registered with addListener.
   * @param listener - Callback function.
   */
  removeListener(listener: (data: T) => void): void;
  /**
   * Registers a listener.
   * @param listener - Callback function.
   * @deprecated Use addListener.
   */
  on(listener: (data: T) => void): void;
  /**
   * Unregisters a listener.
   * @param listener - Callback function.
   * @deprecated Use removeListener.
   */
  off(listener: (data: T) => void): void;
  /**
   * Registers a listener then unregisters the listener after one event emission.
   * @param listener - Callback function.
   * @deprecated Use addListener.
   */
  once(listener: (data: T) => void): void;
}

/**
 * Creates an {@link Emitter}.
 * @param eventEmitter - An event emitter.
 * @param eventName - Event name.
 * @internal
 */
export function _makeEmitter<T>(eventEmitter: EventEmitter, eventName: string = "event"): Emitter<T> {
  return {
    addListener: (listener: (data: T) => void, options: { once?: boolean } = {}): void => {
      if (options.once) {
        eventEmitter.once(eventName, listener);
      } else {
        eventEmitter.addListener(eventName, listener);
      }
    },
    removeListener: (listener: (data: T) => void): void => {
      eventEmitter.removeListener(eventName, listener);
    },
    on: (listener: (data: T) => void): void => {
      eventEmitter.on(eventName, listener);
    },
    off: (listener: (data: T) => void): void => {
      eventEmitter.removeListener(eventName, listener);
    },
    once: (listener: (data: T) => void): void => {
      eventEmitter.once(eventName, listener);
    }
  };
}