import { createContext, useCallback, useEffect, useMemo, useState } from "react";
import Script from "next/script";
import useLocalStorage from "../hooks/useLocalStorage";
import useMedia from "../hooks/useMedia";
import type { Context, PropsWithChildren } from "react";
export const ThemeContext: Context<{
/**
* If the user's theme preference is unset, this returns whether the system preference resolved to "light" or "dark".
* If the user's theme preference is set, the preference is returned instead, regardless of their system's theme.
*/
activeTheme: string;
/** Update the theme manually and save to local storage. */
setTheme: (theme: string) => void;
}> = createContext({
activeTheme: "",
// eslint-disable-next-line @typescript-eslint/no-unused-vars, @typescript-eslint/no-empty-function
setTheme: (_) => {},
});
// provider used once in _app.tsx to wrap entire app
export const ThemeProvider = ({
classNames,
storageKey = "theme",
children,
}: PropsWithChildren<{
/** Mapping of theme name ("light", "dark") to the corresponding ``'s class names. */
classNames: {
[themeName: string]: string;
};
/** Key to use when saving preferred theme to local storage. Defaults to "theme". */
storageKey?: string;
}>) => {
// keep track of if/when the user has set their theme *on this site*
const [preferredTheme, setPreferredTheme] = useLocalStorage(storageKey);
// keep track of changes to the user's OS/browser dark mode setting
const [systemTheme, setSystemTheme] = useState("");
// hook into system `prefers-dark-mode` setting
// https://web.dev/prefers-color-scheme/#the-prefers-color-scheme-media-query
const isSystemDark = useMedia("(prefers-color-scheme: dark)");
// get the theme names (light, dark) via passed-in classnames' keys
const themeNames = Object.keys(classNames);
// updates the DOM and optionally saves the new theme to local storage
const changeTheme = useCallback(
(theme: string, updateStorage?: boolean) => {
if (updateStorage) {
setPreferredTheme(theme);
}
// remove all theme classes first to start fresh
const all = Object.values(classNames);
document.documentElement.classList.remove(...all);
document.documentElement.classList.add(classNames[theme]);
},
[classNames, setPreferredTheme]
);
// listen for changes in OS preference
useEffect(() => {
// translate boolean to theme string
const systemResolved = isSystemDark ? "dark" : "light";
// keep track of the system theme whether or not we override it manually
setSystemTheme(systemResolved);
// only actually change the theme if preference is unset (and *don't* save new theme to storage)
if (!preferredTheme || !themeNames.includes(preferredTheme)) {
changeTheme(systemResolved, false);
}
}, [changeTheme, themeNames, preferredTheme, isSystemDark]);
// color-scheme handling (tells browser how to render built-in elements like forms, scrollbars, etc.)
useEffect(() => {
// only "light" and "dark" are valid here
// https://web.dev/color-scheme/#the-color-scheme-css-property
const colorScheme = preferredTheme && ["light", "dark"].includes(preferredTheme) ? preferredTheme : systemTheme;
document.documentElement.style?.setProperty("color-scheme", colorScheme);
}, [preferredTheme, systemTheme]);
const providerValues = useMemo(
() => ({
activeTheme: preferredTheme && themeNames.includes(preferredTheme) ? preferredTheme : systemTheme,
setTheme: (theme: string) => {
// force save to local storage
changeTheme(theme, true);
},
}),
[changeTheme, preferredTheme, systemTheme, themeNames]
);
return (
<>
{/* eslint-disable-next-line @next/next/no-before-interactive-script-outside-document */}
{children}
);
};
// debugging help pls
if (process.env.NODE_ENV !== "production") {
ThemeContext.displayName = "ThemeContext";
}