michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0: * License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0: * You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: this.EXPORTED_SYMBOLS = ["ScrollPosition"];
michael@0: 
michael@0: const Ci = Components.interfaces;
michael@0: 
michael@0: /**
michael@0:  * It provides methods to collect and restore scroll positions for single
michael@0:  * frames and frame trees.
michael@0:  *
michael@0:  * This is a child process module.
michael@0:  */
michael@0: this.ScrollPosition = Object.freeze({
michael@0:   /**
michael@0:    * Collects scroll position data for any given |frame| in the frame hierarchy.
michael@0:    *
michael@0:    * @param frame (DOMWindow)
michael@0:    *
michael@0:    * @return {scroll: "x,y"} e.g. {scroll: "100,200"}
michael@0:    *         Returns null when there is no scroll data we want to store for the
michael@0:    *         given |frame|.
michael@0:    */
michael@0:   collect: function (frame) {
michael@0:     let ifreq = frame.QueryInterface(Ci.nsIInterfaceRequestor);
michael@0:     let utils = ifreq.getInterface(Ci.nsIDOMWindowUtils);
michael@0:     let scrollX = {}, scrollY = {};
michael@0:     utils.getScrollXY(false /* no layout flush */, scrollX, scrollY);
michael@0: 
michael@0:     if (scrollX.value || scrollY.value) {
michael@0:       return {scroll: scrollX.value + "," + scrollY.value};
michael@0:     }
michael@0: 
michael@0:     return null;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Restores scroll position data for any given |frame| in the frame hierarchy.
michael@0:    *
michael@0:    * @param frame (DOMWindow)
michael@0:    * @param value (object, see collect())
michael@0:    */
michael@0:   restore: function (frame, value) {
michael@0:     let match;
michael@0: 
michael@0:     if (value && (match = /(\d+),(\d+)/.exec(value))) {
michael@0:       frame.scrollTo(match[1], match[2]);
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Restores scroll position data for the current frame hierarchy starting at
michael@0:    * |root| using the given scroll position |data|.
michael@0:    *
michael@0:    * If the given |root| frame's hierarchy doesn't match that of the given
michael@0:    * |data| object we will silently discard data for unreachable frames. We
michael@0:    * may as well assign scroll positions to the wrong frames if some were
michael@0:    * reordered or removed.
michael@0:    *
michael@0:    * @param root (DOMWindow)
michael@0:    * @param data (object)
michael@0:    *        {
michael@0:    *          scroll: "100,200",
michael@0:    *          children: [
michael@0:    *            {scroll: "100,200"},
michael@0:    *            null,
michael@0:    *            {scroll: "200,300", children: [ ... ]}
michael@0:    *          ]
michael@0:    *        }
michael@0:    */
michael@0:   restoreTree: function (root, data) {
michael@0:     if (data.hasOwnProperty("scroll")) {
michael@0:       this.restore(root, data.scroll);
michael@0:     }
michael@0: 
michael@0:     if (!data.hasOwnProperty("children")) {
michael@0:       return;
michael@0:     }
michael@0: 
michael@0:     let frames = root.frames;
michael@0:     data.children.forEach((child, index) => {
michael@0:       if (child && index < frames.length) {
michael@0:         this.restoreTree(frames[index], child);
michael@0:       }
michael@0:     });
michael@0:   }
michael@0: });