( function () {

	class SelectionHelper {

		constructor( selectionBox, renderer, cssClassName ) {

			this.element = document.createElement( 'div' );
			this.element.classList.add( cssClassName );
			this.element.style.pointerEvents = 'none';
			this.renderer = renderer;
			this.startPoint = new THREE.Vector2();
			this.pointTopLeft = new THREE.Vector2();
			this.pointBottomRight = new THREE.Vector2();
			this.isDown = false;
			this.renderer.domElement.addEventListener( 'pointerdown', function ( event ) {

				this.isDown = true;
				this.onSelectStart( event );

			}.bind( this ) );
			this.renderer.domElement.addEventListener( 'pointermove', function ( event ) {

				if ( this.isDown ) {

					this.onSelectMove( event );

				}

			}.bind( this ) );
			this.renderer.domElement.addEventListener( 'pointerup', function ( event ) {

				this.isDown = false;
				this.onSelectOver( event );

			}.bind( this ) );

		}

		onSelectStart( event ) {

			this.renderer.domElement.parentElement.appendChild( this.element );
			this.element.style.left = event.clientX + 'px';
			this.element.style.top = event.clientY + 'px';
			this.element.style.width = '0px';
			this.element.style.height = '0px';
			this.startPoint.x = event.clientX;
			this.startPoint.y = event.clientY;

		}

		onSelectMove( event ) {

			this.pointBottomRight.x = Math.max( this.startPoint.x, event.clientX );
			this.pointBottomRight.y = Math.max( this.startPoint.y, event.clientY );
			this.pointTopLeft.x = Math.min( this.startPoint.x, event.clientX );
			this.pointTopLeft.y = Math.min( this.startPoint.y, event.clientY );
			this.element.style.left = this.pointTopLeft.x + 'px';
			this.element.style.top = this.pointTopLeft.y + 'px';
			this.element.style.width = this.pointBottomRight.x - this.pointTopLeft.x + 'px';
			this.element.style.height = this.pointBottomRight.y - this.pointTopLeft.y + 'px';

		}

		onSelectOver() {

			this.element.parentElement.removeChild( this.element );

		}

	}

	THREE.SelectionHelper = SelectionHelper;

} )();