export type Listener<T> = (event: T) => void

export type EventMap = {
	[K in string]: unknown
}

export abstract class EventEmitter<TEventMap = EventMap> {
	private _listeners: {
		[K in keyof TEventMap]?: [Listener<TEventMap[K]>, string | null][]
	} = {}

	on<TEventType extends keyof TEventMap>(
		event: TEventType,
		listener: Listener<TEventMap[TEventType]>,
		key: string | null = null,
	): void {
		this._listeners[event] = [...(this._listeners[event] ?? []), [listener, key]]
	}

	off<TEventType extends keyof TEventMap>(
		event: TEventType,
		listenerOrKey: Listener<TEventMap[TEventType]> | string,
	): void {
		this._listeners[event] = (this._listeners[event] ?? []).filter(([listener, key]) =>
			typeof listenerOrKey === "function" ? listener !== listenerOrKey : key !== listenerOrKey,
		)
	}

	emit<TEventType extends keyof TEventMap>(
		event: TEventType,
		payload: TEventMap[TEventType],
	): void {
		;(this._listeners[event] ?? []).forEach((listener) => listener[0](payload))
	}
}