From 3c9d9ea4025b2aed07b312f8038deb6804240dda Mon Sep 17 00:00:00 2001
From: Roland <roland@learningselfreliance.com>
Date: Thu, 27 Oct 2022 17:35:36 -0600
Subject: [PATCH] Adding systemTheme to match the current system theme. 
 darkTheme and lightTheme now override system preference.

---
 app/src/components/Common.js | 26 ++++++-----
 app/src/components/Theme.js  | 84 ++++++++++++++++++++++++++++--------
 2 files changed, 77 insertions(+), 33 deletions(-)

diff --git a/app/src/components/Common.js b/app/src/components/Common.js
index 63247630..690ce0d9 100644
--- a/app/src/components/Common.js
+++ b/app/src/components/Common.js
@@ -4,7 +4,7 @@ import {Link, NavLink} from "react-router-dom";
 import Message from "semantic-ui-react/dist/commonjs/collections/Message";
 import {useDownloaders, useHotspot, useThrottle} from "../hooks/customHooks";
 import {StatusContext, ThemeContext} from "../contexts/contexts";
-import {Button, CardIcon, darkTheme, Form, Header, Icon, Menu, Popup, Statistic} from "./Theme";
+import {Button, CardIcon, darkTheme, Form, Header, Icon, lightTheme, Menu, Popup, Statistic} from "./Theme";
 
 export const API_URI = `http://${window.location.host}/api`;
 export const VIDEOS_API = `${API_URI}/videos`;
@@ -708,21 +708,19 @@ export function LoadStatistic({label, value, cores, ...props}) {
 }
 
 export function DarkModeToggle() {
-    const {theme, setDarkTheme, setLightTheme} = useContext(ThemeContext);
-    const darkMode = theme === darkTheme;
-
-    const toggleDarkMode = () => {
-        // Save the selection.  The user manually chose the theme.
-        if (darkMode) {
-            setLightTheme(true);
-        } else {
-            setDarkTheme(true);
-        }
+    const {savedTheme, cycleSavedTheme} = useContext(ThemeContext);
+    let iconName = 'lightbulb outline';
+    if (savedTheme === darkTheme) {
+        iconName = 'moon';
+    } else if (savedTheme === lightTheme) {
+        iconName = 'sun';
     }
 
-    return <>
-        <Toggle checked={darkMode} onChange={toggleDarkMode} icon={darkMode ? 'moon' : 'sun'}/>
-    </>
+    return <Icon
+        name={iconName}
+        onClick={cycleSavedTheme}
+        style={{cursor: 'pointer'}}
+    />
 }
 
 
diff --git a/app/src/components/Theme.js b/app/src/components/Theme.js
index cfa5ed0f..c05494a3 100644
--- a/app/src/components/Theme.js
+++ b/app/src/components/Theme.js
@@ -25,6 +25,9 @@ import {
 
 export const darkTheme = 'dark';
 export const lightTheme = 'light';
+export const defaultTheme = lightTheme;
+export const systemTheme = 'system';
+export const themeSessionKey = 'color-scheme';
 
 export function ThemeWrapper({children, ...props}) {
     if (Object.keys(props).length > 0) {
@@ -32,11 +35,17 @@ export function ThemeWrapper({children, ...props}) {
         console.error('ThemeWrapper does not support props!');
     }
 
+    // Properties to manipulate elements with theme.
+    // Example <p {...s}>This paragraph changes style</p>
     const [i, setI] = useState({});
     const [s, setS] = useState({});
     const [t, setT] = useState({});
     const [inverted, setInverted] = useState('');
-    const [theme, setTheme] = useState();
+
+    // theme can be one of [darkTheme, lightTheme]
+    const [theme, setTheme] = useState(defaultTheme);
+    // savedTheme can be one of [null, darkTheme, lightTheme, systemTheme]
+    const [savedTheme, setSavedTheme] = useState(localStorage.getItem('color-scheme'));
 
     const setDarkTheme = (save = false) => {
         console.debug('setDarkTheme');
@@ -64,26 +73,58 @@ export function ThemeWrapper({children, ...props}) {
         }
     }
 
-    const saveTheme = (value) => {
-        console.debug('saveTheme', value);
-        localStorage.setItem('color-scheme', value);
+    const setSystemTheme = () => {
+        console.debug('setSystemTheme');
+        saveTheme(systemTheme);
     }
 
-    useEffect(() => {
-        const colorScheme = localStorage.getItem('color-scheme');
-        if (colorScheme === darkTheme) {
-            // User saved dark theme.
-            setDarkTheme();
-        } else if (colorScheme === lightTheme) {
-            // User saved light theme.
-            setLightTheme();
-        } else {
-            // No saved theme, use the systems color scheme first, if no system theme, use dark.
-            window.matchMedia('(prefers-color-scheme: dark)').matches ? setDarkTheme() : setLightTheme();
+    const saveTheme = (value) => {
+        setSavedTheme(value);
+        localStorage.setItem(themeSessionKey, value);
+    }
+
+    const cycleSavedTheme = (e) => {
+        // Cycle: System -> Dark -> Light
+        if (e) {
+            e.preventDefault();
         }
-        // Add listener to match the system theme.
-        window.matchMedia('(prefers-color-scheme: dark)').addEventListener(
-            'change', (e) => e.matches ? setDarkTheme() : setLightTheme());
+        if (savedTheme === systemTheme || savedTheme == null) {
+            saveTheme(darkTheme);
+        } else if (savedTheme === darkTheme) {
+            saveTheme(lightTheme);
+        } else if (savedTheme === lightTheme) {
+            saveTheme(systemTheme);
+        } else {
+            console.error(`Unknown theme! savedTheme=${savedTheme}`);
+        }
+        applyTheme();
+    }
+
+    const matchTheme = () => {
+        // Returns darkTheme if saved theme is dark, lightTheme if saved theme is dark,
+        // darkTheme if system prefers dark, otherwise lightTheme.
+        const colorScheme = localStorage.getItem(themeSessionKey);
+        setSavedTheme(colorScheme);
+        if (colorScheme === darkTheme) {
+            return darkTheme;
+        } else if (colorScheme === lightTheme) {
+            return lightTheme
+        }
+        return window.matchMedia('(prefers-color-scheme: dark)').matches ? darkTheme : lightTheme;
+    }
+
+    const applyTheme = () => {
+        const match = matchTheme();
+        if (match === darkTheme) {
+            setDarkTheme();
+        } else {
+            setLightTheme();
+        }
+    };
+
+    useEffect(() => {
+        applyTheme();
+        window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', applyTheme);
     }, []);
 
     const themeValue = {
@@ -91,7 +132,12 @@ export function ThemeWrapper({children, ...props}) {
         t, // Used to invert text.
         s, // Used to invert the style some elements.
         inverted, // Used to add "invert" to className.
-        theme, setDarkTheme, setLightTheme
+        theme,
+        savedTheme,
+        setDarkTheme,
+        setLightTheme,
+        setSystemTheme,
+        cycleSavedTheme,
     };
 
     return <ThemeContext.Provider value={themeValue}>