backnotprop__plannotator/components/ThemeProvider.tsx

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

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

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

const ThemeProviderContext = createContext<ThemeProviderState>({
  theme: 'dark',
  setTheme: () => null,
});

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

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

  useEffect(() => {
    const root = window.document.documentElement;

    // Remove light class (dark is default, no class needed)
    root.classList.remove('light');

    let effectiveTheme = theme;
    if (theme === 'system') {
      effectiveTheme = window.matchMedia('(prefers-color-scheme: light)').matches
        ? 'light'
        : 'dark';
    }

    // Only add 'light' class when in light mode
    if (effectiveTheme === 'light') {
      root.classList.add('light');
    }
  }, [theme]);

  // Listen for system theme changes
  useEffect(() => {
    if (theme !== 'system') return;

    const mediaQuery = window.matchMedia('(prefers-color-scheme: light)');
    const handleChange = () => {
      const root = window.document.documentElement;
      root.classList.remove('light');
      if (mediaQuery.matches) {
        root.classList.add('light');
      }
    };

    mediaQuery.addEventListener('change', handleChange);
    return () => mediaQuery.removeEventListener('change', handleChange);
  }, [theme]);

  const value = {
    theme,
    setTheme: (newTheme: Theme) => {
      localStorage.setItem(storageKey, newTheme);
      setTheme(newTheme);
    },
  };

  return (
    <ThemeProviderContext.Provider value={value}>
      {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;
};