/**
 * 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 = any> = (event?: T) => void
export type WildcardHandler = (type: EventType, event?: any) => void

// An array of all currently registered event handlers for a type
export type EventHandlerList = Array<Handler>
export type WildCardEventHandlerList = Array<WildcardHandler>

// A map of event types and their corresponding event handlers.
export type EventHandlerMap = Map<EventType, EventHandlerList | WildCardEventHandlerList>

export interface Emitter {
  all: EventHandlerMap

  on<T = any>(type: EventType, handler: Handler<T>): void
  on(type: '*', handler: WildcardHandler): void

  off<T = any>(type: EventType, handler: Handler<T>): void
  off(type: '*', handler: WildcardHandler): void

  emit<T = any>(type: EventType, event?: T): void
  emit(type: '*', event?: any): void
  clear(): void
}

/**
 * Mitt: Tiny (~200b) functional event emitter / pubsub.
 * @name mitt
 * @returns {Mitt} 1
 */
export function mitt(all?: EventHandlerMap): Emitter {
  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<T = any>(type: EventType, handler: Handler<T>) {
      const handlers = all?.get(type)
      const added = handlers && handlers.push(handler)
      if (!added)
        all?.set(type, [handler])
    },

    /**
     * Remove an event handler for the given type.
     * @param {string|symbol} type Type of event to unregister `handler` from, or `"*"`
     * @param {Function} handler Handler function to remove
     * @memberOf mitt
     */
    off<T = any>(type: EventType, handler: Handler<T>) {
      const handlers = all?.get(type)
      if (handlers)
        handlers.splice(handlers.indexOf(handler) >>> 0, 1)
    },

    /**
     * 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<T = any>(type: EventType, evt: T) {
      // map
      ((all?.get(type) || []) as EventHandlerList).slice().forEach((handler) => {
        handler(evt)
      });
      // map
      ((all?.get('*') || []) as WildCardEventHandlerList).slice().forEach((handler) => {
        handler(type, evt)
      })
    },

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