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/*
* Copyright (C) 2023 Yomitan Authors
* Copyright (C) 2020-2022 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 {
/**
* Creates a new instance of the class.
* @param {?string} autofocusElementSelector A selector string which can be used to specify an element which
* should be automatically focused on prepare.
*/
constructor(autofocusElementSelector=null) {
this._autofocusElement = (autofocusElementSelector !== null ? document.querySelector(autofocusElementSelector) : null);
this._contentScrollFocusElement = document.querySelector('#content-scroll-focus');
}
/**
* Initializes the instance.
*/
prepare() {
window.addEventListener('focus', this._onWindowFocus.bind(this), false);
this._updateFocusedElement(false);
if (this._autofocusElement !== null && document.activeElement !== this._autofocusElement) {
this._autofocusElement.focus({preventScroll: true});
}
}
/**
* Removes focus from a given element.
* @param {Element} element The element to remove focus from.
*/
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;
}
}
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