interface EventsMap {
  [event: string]: any;
}
interface DefaultEvents extends EventsMap {
  [event: string]: (...args: any) => void;
}
export interface Unsubscribe {
  (): void;
}
export interface Emitter<Events extends EventsMap = DefaultEvents> {
  /**
   * Calls each of the listeners registered for a given event.
   *
   * ```js
   * ee.emit('tick', tickType, tickDuration)
   * ```
   *
   * @param event The event name.
   * @param args The arguments for listeners.
   */
  emit<K extends keyof Events>(
    this: this,
    event: K,
    ...args: Parameters<Events[K]>
  ): void;

  /**
   * Event names in keys and arrays with listeners in values.
   *
   * ```js
   * emitter1.events = emitter2.events
   * emitter2.events = { }
   * ```
   */
  events: Partial<{[E in keyof Events]: Events[E][]}>;

  /**
   * Add a listener for a given event.
   *
   * ```js
   * const unbind = ee.on('tick', (tickType, tickDuration) => {
   *   count += 1
   * })
   *
   * disable () {
   *   unbind()
   * }
   * ```
   *
   * @param event The event name.
   * @param cb The listener function.
   * @returns Unbind listener from event.
   */
  on<K extends keyof Events>(this: this, event: K, cb: Events[K]): Unsubscribe;
}

/**
 * Create event emitter.
 *
 * ```js
 * import { createNanoEvents } from 'nanoevents'
 *
 * class Ticker {
 *   constructor() {
 *     this.emitter = createNanoEvents()
 *   }
 *   on(...args) {
 *     return this.emitter.on(...args)
 *   }
 *   tick() {
 *     this.emitter.emit('tick')
 *   }
 * }
 * ```
 */
export function createNanoEvents<
  Events extends EventsMap = DefaultEvents,
>(): Emitter<Events>;

/**
 * An interface for mixins that expose the `on` function (without the emitter
 * bound to `this`)
 *
 * ```js
 * import { createNanoEvents } from 'nanoevents'
 *
 * class Ticker implements EmitterMixin<Events> {
 *   constructor() {
 *     this.emitter = createNanoEvents()
 *   }
 *   on(...args) {
 *     return this.emitter.on(...args)
 *   }
 *   tick() {
 *     this.emitter.emit('tick')
 *   }
 * }
 * ```
 */
export interface EmitterMixin<Events extends EventsMap = DefaultEvents> {
  on<K extends keyof Events>(event: K, cb: Events[K]): Unsubscribe;
}