/**
 * copy to https://github.com/developit/mitt
 * Expand clear method
 */
export type EventType = string | symbol;

// An event handler can take an optional event argument
// and should not return a value
export type Handler<T = unknown> = (event: T) => void;
export type WildcardHandler<T = Record<string, unknown>> = (
  type: keyof T,
  event: T[keyof T],
) => void;

// An array of all currently registered event handlers for a type
export type EventHandlerList<T = unknown> = Array<Handler<T>>;
export type WildCardEventHandlerList<T = Record<string, unknown>> = Array<WildcardHandler<T>>;

// A map of event types and their corresponding event handlers.
export type EventHandlerMap<Events extends Record<EventType, unknown>> = Map<
  keyof Events | '*',
  EventHandlerList<Events[keyof Events]> | WildCardEventHandlerList<Events>
>;

export interface Emitter<Events extends Record<EventType, unknown>> {
  all: EventHandlerMap<Events>;

  on<Key extends keyof Events>(type: Key, handler: Handler<Events[Key]>): void;
  on(type: '*', handler: WildcardHandler<Events>): void;

  off<Key extends keyof Events>(type: Key, handler?: Handler<Events[Key]>): void;
  off(type: '*', handler: WildcardHandler<Events>): void;

  emit<Key extends keyof Events>(type: Key, event: Events[Key]): void;
  emit<Key extends keyof Events>(type: undefined extends Events[Key] ? Key : never): void;
  clear(): void;
}

/**
 * Mitt: Tiny (~200b) functional event emitter / pubsub.
 * @name mitt
 * @returns {Mitt}
 */
export function mitt<Events extends Record<EventType, unknown>>(
  all?: EventHandlerMap<Events>,
): Emitter<Events> {
  type GenericEventHandler = Handler<Events[keyof Events]> | WildcardHandler<Events>;
  all = all || new Map();

  return {
    /**
     * A Map of event names to registered handler functions.
     */
    all,

    /**
     * Register an event handler for the given type.
     * @param {string|symbol} type Type of event to listen for, or `'*'` for all events
     * @param {Function} handler Function to call in response to given event
     * @memberOf mitt
     */
    on<Key extends keyof Events>(type: Key, handler: GenericEventHandler) {
      const handlers: Array<GenericEventHandler> | undefined = all!.get(type);
      if (handlers) {
        handlers.push(handler);
      } else {
        all!.set(type, [handler] as EventHandlerList<Events[keyof Events]>);
      }
    },

    /**
     * Remove an event handler for the given type.
     * If `handler` is omitted, all handlers of the given type are removed.
     * @param {string|symbol} type Type of event to unregister `handler` from (`'*'` to remove a wildcard handler)
     * @param {Function} [handler] Handler function to remove
     * @memberOf mitt
     */
    off<Key extends keyof Events>(type: Key, handler?: GenericEventHandler) {
      const handlers: Array<GenericEventHandler> | undefined = all!.get(type);
      if (handlers) {
        if (handler) {
          handlers.splice(handlers.indexOf(handler) >>> 0, 1);
        } else {
          all!.set(type, []);
        }
      }
    },

    /**
     * Invoke all handlers for the given type.
     * If present, `'*'` handlers are invoked after type-matched handlers.
     *
     * Note: Manually firing '*' handlers is not supported.
     *
     * @param {string|symbol} type The event type to invoke
     * @param {Any} [evt] Any value (object is recommended and powerful), passed to each handler
     * @memberOf mitt
     */
    emit<Key extends keyof Events>(type: Key, evt?: Events[Key]) {
      let handlers = all!.get(type);
      if (handlers) {
        (handlers as EventHandlerList<Events[keyof Events]>).slice().forEach((handler) => {
          handler(evt as Events[Key]);
        });
      }

      handlers = all!.get('*');
      if (handlers) {
        (handlers as WildCardEventHandlerList<Events>).slice().forEach((handler) => {
          handler(type, evt as Events[Key]);
        });
      }
    },

    /**
     * Clear all
     */
    clear() {
      this.all.clear();
    },
  };
}