Raiondesu/eventhoven

import { TMetaEvents, metaEvents, EMetaEvents } from './meta-events';
import { TEventMap, THandlerOf, TLastParams } from './types';

export type TEmitReturn<M extends TEventMap, E extends keyof M> = Promise<Array<ReturnType<THandlerOf<M, E>>>>;

/**
 * Event-emitter factory creator
 *
 * Creates an emitter factory for specific events.
 *
 * @param eventMap - an event collection to create an emitter for
 */
export const emit = <M extends TEventMap>(
  eventMap: M
) =>
/**
 * Emitter factory for a specific event collection
 *
 * Creates an emitter for a specific event
 *
 * @param event - the name of the event to emit
 */
<E extends keyof M>(event: E) =>
/**
 * Emits an event with proper arguments
 */
(...args: TLastParams<THandlerOf<M, E>>): TEmitReturn<M, E> => (
  emitMeta(EMetaEvents.EMIT)(eventMap, event, args),
  Promise.all(
    [...(eventMap[event] || [])].map(
      ([handler, unsubscribe]) => handler
        && handler({ event, unsubscribe }, ...args)
    ) as Array<ReturnType<THandlerOf<M, E>>>
  )
);

/**
 * Emits a meta-event
 *
 * @param event - a meta-event to emit
 */
export const emitMeta = <E extends EMetaEvents>(event: E) => (
  ...args: TLastParams<THandlerOf<TMetaEvents, E>>
): Promise<void[]> => args[0] !== metaEvents
  ? emit(metaEvents)(event)(...args)
  : Promise.resolve([]);