/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import {Directive, ElementRef, OnInit, OnDestroy, NgZone} from '@angular/core';
import {Observable} from 'rxjs/Observable';
import {Subject} from 'rxjs/Subject';
import {ScrollDispatcher} from './scroll-dispatcher';


/**
 * Sends an event when the directive's element is scrolled. Registers itself with the
 * ScrollDispatcher service to include itself as part of its collection of scrolling events that it
 * can be listened to through the service.
 */
@Directive({
  selector: '[cdk-scrollable], [cdkScrollable]'
})
export class CdkScrollable implements OnInit, OnDestroy {
  private _elementScrolled: Subject<Event> = new Subject();
  private _scrollListener = (event: Event) => this._elementScrolled.next(event);

  constructor(private _elementRef: ElementRef,
              private _scroll: ScrollDispatcher,
              private _ngZone: NgZone) {}

  ngOnInit() {
    this._ngZone.runOutsideAngular(() => {
      this.getElementRef().nativeElement.addEventListener('scroll', this._scrollListener);
    });

    this._scroll.register(this);
  }

  ngOnDestroy() {
    this._scroll.deregister(this);

    if (this._scrollListener) {
      this.getElementRef().nativeElement.removeEventListener('scroll', this._scrollListener);
    }
  }

  /**
   * Returns observable that emits when a scroll event is fired on the host element.
   */
  elementScrolled(): Observable<any> {
    return this._elementScrolled.asObservable();
  }

  getElementRef(): ElementRef {
    return this._elementRef;
  }
}