bioai-platform/frontend/src/contexts/theme.tsx

'use client';

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

type Theme = 'light' | 'dark';

interface ThemeContextType {
  theme: Theme;
  toggle: () => void;
  setTheme: (t: Theme) => void;
}

const ThemeContext = createContext<ThemeContextType>({
  theme: 'light',
  toggle: () => {},
  setTheme: () => {},
});

function getInitialTheme(): Theme {
  if (typeof window === 'undefined') return 'light';
  const stored = localStorage.getItem('bio-nexus-theme') as Theme | null;
  if (stored === 'light' || stored === 'dark') return stored;
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>('light');

  useEffect(() => {
    setThemeState(getInitialTheme());
  }, []);

  useEffect(() => {
    const root = document.documentElement;
    root.classList.toggle('dark', theme === 'dark');
    localStorage.setItem('bio-nexus-theme', theme);
  }, [theme]);

  const toggle = () => setThemeState((t) => (t === 'dark' ? 'light' : 'dark'));
  const setTheme = (t: Theme) => setThemeState(t);

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

export const useTheme = () => useContext(ThemeContext);