/**
 * EvEmitter v2.0.0
 * Lil' event emitter
 * MIT License
 */

( function( global, factory ) {
  // universal module definition
  if ( typeof module == 'object' && module.exports ) {
    // CommonJS - Browserify, Webpack
    module.exports = factory();
  } else {
    // Browser globals
    global.EvEmitter = factory();
  }

}( typeof window != 'undefined' ? window : this, function() {

function EvEmitter() {}

let proto = EvEmitter.prototype;

proto.on = function( eventName, listener ) {
  if ( !eventName || !listener ) return this;

  // set events hash
  let events = this._events = this._events || {};
  // set listeners array
  let listeners = events[ eventName ] = events[ eventName ] || [];
  // only add once
  if ( !listeners.includes( listener ) ) {
    listeners.push( listener );
  }

  return this;
};

proto.once = function( eventName, listener ) {
  if ( !eventName || !listener ) return this;

  // add event
  this.on( eventName, listener );
  // set once flag
  // set onceEvents hash
  let onceEvents = this._onceEvents = this._onceEvents || {};
  // set onceListeners object
  let onceListeners = onceEvents[ eventName ] = onceEvents[ eventName ] || {};
  // set flag
  onceListeners[ listener ] = true;

  return this;
};

proto.off = function( eventName, listener ) {
  let listeners = this._events && this._events[ eventName ];
  if ( !listeners || !listeners.length ) return this;

  let index = listeners.indexOf( listener );
  if ( index != -1 ) {
    listeners.splice( index, 1 );
  }

  return this;
};

proto.emitEvent = function( eventName, args ) {
  let listeners = this._events && this._events[ eventName ];
  if ( !listeners || !listeners.length ) return this;

  // copy over to avoid interference if .off() in listener
  listeners = listeners.slice( 0 );
  args = args || [];
  // once stuff
  let onceListeners = this._onceEvents && this._onceEvents[ eventName ];

  for ( let listener of listeners ) {
    let isOnce = onceListeners && onceListeners[ listener ];
    if ( isOnce ) {
      // remove listener
      // remove before trigger to prevent recursion
      this.off( eventName, listener );
      // unset once flag
      delete onceListeners[ listener ];
    }
    // trigger listener
    listener.apply( this, args );
  }

  return this;
};

proto.allOff = function() {
  delete this._events;
  delete this._onceEvents;
  return this;
};

return EvEmitter;

} ) );