99 lines
2.3 KiB
TypeScript
99 lines
2.3 KiB
TypeScript
import {
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createContext,
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useCallback,
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useContext,
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useEffect,
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useMemo,
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useState,
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} from "react";
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export type Theme = "light" | "dark";
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type ThemeProviderState = {
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/** The resolved, active theme ("light" | "dark") applied to the DOM. */
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theme: Theme;
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setTheme: (theme: Theme) => void;
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toggleTheme: () => void;
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};
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const ThemeContext = createContext<ThemeProviderState>({
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theme: "dark",
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setTheme: () => {},
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toggleTheme: () => {},
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});
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const SYSTEM_DARK_QUERY = "(prefers-color-scheme: dark)";
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// ---- system theme store ----
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function systemThemeQuery() {
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if (typeof window === "undefined" || !window.matchMedia) return null;
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return window.matchMedia(SYSTEM_DARK_QUERY);
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}
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function systemThemeSnapshot(): Theme {
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return systemThemeQuery()?.matches ? "dark" : "light";
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}
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function applyClass(t: Theme) {
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const root = document.documentElement;
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if (t === "dark") {
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root.classList.add("dark");
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root.classList.remove("light");
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} else {
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root.classList.add("light");
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root.classList.remove("dark");
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}
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}
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// ---- provider ----
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export function ThemeProvider({ children }: { children: React.ReactNode }) {
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const [theme, setThemeState] = useState<Theme>(systemThemeSnapshot);
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const setTheme = useCallback(
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(next: Theme) => {
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// Direct DOM write to prevent visual lag on transition.
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setThemeState(next);
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applyClass(next);
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},
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[],
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);
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const toggleTheme = useCallback(() => {
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setTheme(theme === "dark" ? "light" : "dark");
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}, [theme, setTheme]);
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useEffect(() => {
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const mql = systemThemeQuery();
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if (!mql) return;
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const syncSystemTheme = () => setThemeState(mql.matches ? "dark" : "light");
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syncSystemTheme();
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if (mql.addEventListener) {
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mql.addEventListener("change", syncSystemTheme);
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return () => mql.removeEventListener("change", syncSystemTheme);
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}
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mql.addListener?.(syncSystemTheme);
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return () => mql.removeListener?.(syncSystemTheme);
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}, []);
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// Sync the class whenever the resolved theme changes.
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useEffect(() => {
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applyClass(theme);
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}, [theme]);
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const value = useMemo<ThemeProviderState>(
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() => ({ theme, setTheme, toggleTheme }),
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[theme, setTheme, toggleTheme],
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);
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return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
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}
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export function useTheme() {
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return useContext(ThemeContext);
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}
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