/**
 * @license
 * Copyright Google Inc. 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
 */
/* tslint:disable:array-type member-access variable-name typedef
 only-arrow-functions directive-class-suffix component-class-suffix
 component-selector*/
import {ViewportRuler} from '../position/viewport-ruler';

import {ScrollStrategy} from './scroll-strategy';

/**
 * Strategy that will prevent the user from scrolling while the overlay is
 * visible.
 */
export class BlockScrollStrategy implements ScrollStrategy {
  private _previousHTMLStyles = {top: '', left: ''};
  private _previousScrollPosition: {top: number, left: number};
  private _isEnabled = false;

  constructor(private _viewportRuler: ViewportRuler) {}

  attach() {
    //
  }

  enable() {
	if (this._canBeEnabled()) {
		const root = document.documentElement;

		this._previousScrollPosition =
			this._viewportRuler.getViewportScrollPosition();

      // Cache the previous inline styles in case the user had set them.
		this._previousHTMLStyles.left = root.style.left || '';
		this._previousHTMLStyles.top = root.style.top || '';

      // Note: we're using the `html` node, instead of the `body`, because the
      // `body` may have the user agent margin, whereas the `html` is guaranteed
      // not to have one.
		root.style.left = `${- this._previousScrollPosition.left}px`;
		root.style.top = `${- this._previousScrollPosition.top}px`;
		root.classList.add('cdk-global-scrollblock');
		this._isEnabled = true;
	}
  }

  disable() {
	if (this._isEnabled) {
		this._isEnabled = false;
		document.documentElement.style.left = this._previousHTMLStyles.left;
		document.documentElement.style.top = this._previousHTMLStyles.top;
		document.documentElement.classList.remove('cdk-global-scrollblock');
		window.scroll(
			this._previousScrollPosition.left, this._previousScrollPosition.top);
	}
  }

  private _canBeEnabled(): boolean {
    // Since the scroll strategies can't be singletons, we have to use a global
    // CSS class
    // (`cdk-global-scrollblock`) to make sure that we don't try to disable
    // global scrolling multiple times.
	if (document.documentElement.classList.contains('cdk-global-scrollblock') ||
		this._isEnabled) {
		return false;
	}

	const body = document.body;
	const viewport = this._viewportRuler.getViewportRect();
	return body.scrollHeight > viewport.height ||
		body.scrollWidth > viewport.width;
  }
}