evented-service.ts

export type EventsDictionary = Record<
  string, 
  (event: CustomEvent<any>) => void
>
  

// Polyfill of CustomEvent for Node Environments
export class CustomEvent<T> extends Event {
  constructor(type: string, detail: { detail: T }) {
    super(type)
    this.detail = detail.detail
  }
  public readonly detail: T
}


export default class EventedService<
  E_DICTIONARY extends EventsDictionary = EventsDictionary
> {

  constructor() {
    this.#subscribers = {}
  }
  
  /**
   * Collection of active subscribers grouped by event name
   */
  readonly #subscribers: Record<
    PropertyKey, Set<E_DICTIONARY[keyof E_DICTIONARY]>
  >

  
  /**
  *
  * Get the collection of subscribers for an event. 
  * If collections does not yet exist will be created
  *
  */
  private getEventSubscribersCollection<
    E_NAME extends keyof E_DICTIONARY
  >(eventName: E_NAME) : Set{
    if (!this.#subscribers[eventName]){ 
      this.#subscribers[eventName] = new Set()
    }
    return this.#subscribers[eventName]
  }
 

  /**
   * Iterates the list of subscribers and executes the callback
   * for a given event name
   */
  protected dispatchEvent<E_NAME extends keyof E_DICTIONARY>(
    ...[eventName, eventData]: Parameters<E_DICTIONARY[E_NAME]>[0] extends void
      ? [E_NAME]
      : [E_NAME, Parameters<E_DICTIONARY[E_NAME]>[0] extends CustomEvent<infer T> ? T : never]
  ) {
    const eventHandlersCollection = 
    this.getEventSubscribersCollection(eventName)

    const event = new CustomEvent(
      String(eventName), 
      { detail: eventData }
    )

    for (const eventHandler of eventHandlersCollection) {
      eventHandler(event)
      // stop Event Propagation if requested by user
      if (event.cancelBubble) break
    }
    return event
  }

  
  /**
   * Add the provided callback function to the list of subscribers for a given event name
   */
  public subscribe<E_NAME extends keyof E_DICTIONARY, E_HANDLER extends E_DICTIONARY[E_NAME]>(
    eventName: E_NAME,
    eventHandler: E_HANDLER
  ): void {
    const eventHandlersCollection = this.getEventSubscribersCollection(eventName)
    eventHandlersCollection.add(eventHandler)
  }


  /**
   * Remove the provided callback function to the list of subscribers for a given event name
   */
  public unsubscribe<E_NAME extends keyof E_DICTIONARY, E_HANDLER extends E_DICTIONARY[E_NAME]>(
    eventName: E_NAME,
    eventHandler: E_HANDLER
  ): void {
    const eventHandlersCollection = this.getEventSubscribersCollection(eventName)
    eventHandlersCollection.delete(eventHandler)
  }

}