/* * Copyright (C) 2020-2021 Yomichan Authors * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <https://www.gnu.org/licenses/>. */ /** * This class is used to control the document focus when a non-body element contains the main scrollbar. * Web browsers will not automatically focus a custom element with the scrollbar on load, which results in * keyboard shortcuts (e.g. arrow keys) not controlling page scroll. Instead, this class will manually * focus a dummy element inside the main content, which gives keyboard scroll focus to that element. */ class DocumentFocusController { constructor() { this._contentScrollFocusElement = document.querySelector('#content-scroll-focus'); } prepare() { window.addEventListener('focus', this._onWindowFocus.bind(this), false); this._updateFocusedElement(false); } blurElement(element) { if (document.activeElement !== element) { return; } element.blur(); this._updateFocusedElement(false); } // Private _onWindowFocus() { this._updateFocusedElement(false); } _updateFocusedElement(force) { const target = this._contentScrollFocusElement; if (target === null) { return; } const {activeElement} = document; if ( force || activeElement === null || activeElement === document.documentElement || activeElement === document.body ) { // Get selection const selection = window.getSelection(); const selectionRanges1 = this._getSelectionRanges(selection); // Note: This function will cause any selected text to be deselected on Firefox. target.focus({preventScroll: true}); // Restore selection const selectionRanges2 = this._getSelectionRanges(selection); if (!this._areRangesSame(selectionRanges1, selectionRanges2)) { this._setSelectionRanges(selection, selectionRanges1); } } } _getSelectionRanges(selection) { const ranges = []; for (let i = 0, ii = selection.rangeCount; i < ii; ++i) { ranges.push(selection.getRangeAt(i)); } return ranges; } _setSelectionRanges(selection, ranges) { selection.removeAllRanges(); for (const range of ranges) { selection.addRange(range); } } _areRangesSame(ranges1, ranges2) { const ii = ranges1.length; if (ii !== ranges2.length) { return false; } for (let i = 0; i < ii; ++i) { const range1 = ranges1[i]; const range2 = ranges2[i]; try { if ( range1.compareBoundaryPoints(Range.START_TO_START, range2) !== 0 || range1.compareBoundaryPoints(Range.END_TO_END, range2) !== 0 ) { return false; } } catch (e) { return false; } } return true; } }