import { DispatcherEvent, Listener } from '../types';

/**
 * A class that manages event listeners and dispatches events.
 *
 * @remarks
 * This class allows you to add, remove, and check for event listeners, as well as dispatch events to those listeners.
 *
 * @example
 * ```typescript
 * const dispatcher = new EventDispatcher();
 *
 * function onEvent(event: DispatcherEvent) {
 *     console.log(event.type);
 * }
 *
 * dispatcher.addEventListener('testEvent', onEvent);
 * dispatcher.dispatchEvent({ type: 'testEvent' });
 * dispatcher.removeEventListener('testEvent', onEvent);
 * ```
 *
 * @public
 */
export class EventDispatcher {
    private _listeners: { [type: string]: Listener[] } = {};

    /**
     * Adds the specified event listener.
     * @param type event name
     * @param listener handler function
     * @category Methods
     */
    addEventListener(type: string, listener: Listener): void {
        const listeners = this._listeners;

        if (listeners[type] === undefined) listeners[type] = [];

        if (listeners[type].indexOf(listener) === -1) listeners[type].push(listener);
    }

    /**
     * Presence of the specified event listener.
     * @param type event name
     * @param listener handler function
     * @category Methods
     */
    hasEventListener(type: string, listener: Listener): boolean {
        const listeners = this._listeners;

        return listeners[type] !== undefined && listeners[type].indexOf(listener) !== -1;
    }

    /**
     * Removes the specified event listener
     * @param type event name
     * @param listener handler function
     * @category Methods
     */
    removeEventListener(type: string, listener: Listener): void {
        const listeners = this._listeners;
        const listenerArray = listeners[type];

        if (listenerArray !== undefined) {
            const index = listenerArray.indexOf(listener);

            if (index !== -1) listenerArray.splice(index, 1);
        }
    }

    /**
     * Removes all event listeners
     * @param type event name
     * @category Methods
     */
    removeAllEventListeners(type?: string): void {
        if (!type) {
            this._listeners = {};
            return;
        }

        if (Array.isArray(this._listeners[type])) this._listeners[type].length = 0;
    }

    /**
     * Fire an event type.
     * @param event DispatcherEvent
     * @category Methods
     */
    dispatchEvent(event: DispatcherEvent): void {
        const listeners = this._listeners;
        const listenerArray = listeners[event.type];

        if (listenerArray !== undefined) {
            (event as any).target = this;
            const array = listenerArray.slice(0);

            for (let i = 0, l = array.length; i < l; i++) {
                array[i].call(this, event);
            }
        }
    }
}