web/src/components/theme-provider.tsx

import React, { createContext, useContext, useEffect, useState } from 'react';

type Theme = 'dark' | 'light' | 'system';

type ThemeProviderProps = {
  children: React.ReactNode;
  defaultTheme?: Theme;
  storageKey?: string;
};

type ThemeProviderState = {
  theme: Theme;
  setTheme: (theme: Theme) => void;
};

const initialState: ThemeProviderState = {
  theme: 'light',
  setTheme: () => null,
};

const ThemeProviderContext = createContext<ThemeProviderState>(initialState);

export function ThemeProvider({
  children,
  defaultTheme = 'light',
  storageKey = 'vite-ui-theme',
  ...props
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(
    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme,
  );

  useEffect(() => {
    const root = window.document.documentElement;
    root.classList.remove('light', 'dark');
    localStorage.setItem(storageKey, theme);
    root.classList.add(theme);
  }, [storageKey, theme]);

  return (
    <ThemeProviderContext.Provider
      {...props}
      value={{
        theme,
        setTheme,
      }}
    >
      {children}
    </ThemeProviderContext.Provider>
  );
}

export const useTheme = () => {
  const context = useContext(ThemeProviderContext);

  if (context === undefined)
    throw new Error('useTheme must be used within a ThemeProvider');

  return context;
};

export const useIsDarkTheme = () => {
  const { theme } = useTheme();

  return theme === 'dark';
};