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+/*
+ * Copyright (C) 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 theme attributes on DOM elements.
+ */
+class ThemeController {
+ /**
+ * Creates a new instance of the class.
+ * @param {?Element} element A DOM element which theme properties are applied to.
+ */
+ constructor(element) {
+ this._element = element;
+ this._theme = 'default';
+ this._outerTheme = 'default';
+ this._siteTheme = null;
+ this._browserTheme = 'light';
+ }
+
+ /**
+ * Gets the DOM element which theme properties are applied to.
+ * @type {?Element}
+ */
+ get element() {
+ return this._element;
+ }
+
+ /**
+ * Sets the DOM element which theme properties are applied to.
+ * @param {?Element} value The DOM element to assign.
+ */
+ set element(value) {
+ this._element = value;
+ }
+
+ /**
+ * Gets the main theme for the content.
+ * @type {string}
+ */
+ get theme() {
+ return this._theme;
+ }
+
+ /**
+ * Sets the main theme for the content.
+ * @param {string} value The theme value to assign.
+ */
+ set theme(value) {
+ this._theme = value;
+ }
+
+ /**
+ * Gets the outer theme for the content.
+ * @type {string}
+ */
+ get outerTheme() {
+ return this._outerTheme;
+ }
+
+ /**
+ * Sets the outer theme for the content.
+ * @param {string} value The outer theme value to assign.
+ */
+ set outerTheme(value) {
+ this._outerTheme = value;
+ }
+
+ /**
+ * Gets the override value for the site theme.
+ * If this value is `null`, the computed value will be used.
+ * @type {?string}
+ */
+ get siteTheme() {
+ return this._siteTheme;
+ }
+
+ /**
+ * Sets the override value for the site theme.
+ * If this value is `null`, the computed value will be used.
+ * @param {?string} value The site theme value to assign.
+ */
+ set siteTheme(value) {
+ this._siteTheme = value;
+ }
+
+ /**
+ * Gets the browser's preferred color theme.
+ * The value can be either 'light' or 'dark'.
+ * @type {?string}
+ */
+ get browserTheme() {
+ return this._browserTheme;
+ }
+
+ /**
+ * Prepares the instance for use and applies the theme settings.
+ */
+ prepare() {
+ const mediaQueryList = window.matchMedia('(prefers-color-scheme: dark)');
+ mediaQueryList.addEventListener('change', this._onPrefersColorSchemeDarkChange.bind(this));
+ this._onPrefersColorSchemeDarkChange(mediaQueryList);
+ }
+
+ /**
+ * Updates the theme attributes on the target element.
+ * If the site theme value isn't overridden, the current site theme is recomputed.
+ */
+ updateTheme() {
+ if (this._element === null) { return; }
+ const computedSiteTheme = this._siteTheme !== null ? this._siteTheme : this.computeSiteTheme();
+ const data = this._element.dataset;
+ data.theme = this._resolveThemeValue(this._theme, computedSiteTheme);
+ data.outerTheme = this._resolveThemeValue(this._outerTheme, computedSiteTheme);
+ data.siteTheme = computedSiteTheme;
+ data.browserTheme = this._browserTheme;
+ data.themeRaw = this._theme;
+ data.outerThemeRaw = this._outerTheme;
+ }
+
+ /**
+ * Computes the current site theme based on the background color.
+ * @returns {'light'|'dark'} The theme of the site.
+ */
+ computeSiteTheme() {
+ const color = [255, 255, 255];
+ const {documentElement, body} = document;
+ if (documentElement !== null) {
+ this._addColor(color, window.getComputedStyle(documentElement).backgroundColor);
+ }
+ if (body !== null) {
+ this._addColor(color, window.getComputedStyle(body).backgroundColor);
+ }
+ const dark = (color[0] < 128 && color[1] < 128 && color[2] < 128);
+ return dark ? 'dark' : 'light';
+ }
+
+ /**
+ * Event handler for when the preferred browser theme changes.
+ * @param {MediaQueryList|MediaQueryListEvent} detail The object containing event details.
+ * @param {boolean} detail.matches The object containing event details.
+ */
+ _onPrefersColorSchemeDarkChange({matches}) {
+ this._browserTheme = (matches ? 'dark' : 'light');
+ this.updateTheme();
+ }
+
+ /**
+ * Resolves a settings theme value to the actual value which should be used.
+ * @param {string} theme The theme value to resolve.
+ * @param {string} computedSiteTheme The computed site theme value to use for when the theme value is `'auto'`.
+ * @returns {string} The resolved theme value.
+ */
+ _resolveThemeValue(theme, computedSiteTheme) {
+ switch (theme) {
+ case 'auto': return computedSiteTheme;
+ case 'browser': return this._browserTheme;
+ default: return theme;
+ }
+ }
+
+ /**
+ * Adds the value of a CSS color to an accumulation target.
+ * @param {[number, number, number]} target The target color buffer to accumulate into.
+ * @param {string|*} cssColor The CSS color value to add to the target. If this value is not a string,
+ * the target will not be modified.
+ */
+ _addColor(target, cssColor) {
+ if (typeof cssColor !== 'string') { return; }
+
+ const color = this._getColorInfo(cssColor);
+ if (color === null) { return; }
+
+ const a = color[3];
+ if (a <= 0.0) { return; }
+
+ const aInv = 1.0 - a;
+ for (let i = 0; i < 3; ++i) {
+ target[i] = target[i] * aInv + color[i] * a;
+ }
+ }
+
+ /**
+ * Decomposes a CSS color string into its RGBA values.
+ * @param {string} cssColor The color value to decompose. This value is expected to be in the form RGB(r, g, b) or RGBA(r, g, b, a).
+ * @returns {?[number, number, number, number]} The color and alpha values. The color component values range from [0, 255], and the alpha ranges from [0, 1].
+ */
+ _getColorInfo(cssColor) {
+ const m = /^\s*rgba?\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([\d.]+)\s*)?\)\s*$/.exec(cssColor);
+ if (m === null) { return null; }
+
+ const m4 = m[4];
+ return [
+ Number.parseInt(m[1], 10),
+ Number.parseInt(m[2], 10),
+ Number.parseInt(m[3], 10),
+ m4 ? Math.max(0.0, Math.min(1.0, Number.parseFloat(m4))) : 1.0
+ ];
+ }
+}