frontend/src/context/ThemeContext.jsx

import { createContext, useContext, useState, useEffect, useCallback, useMemo } from 'react'

const ThemeContext = createContext(null)

export function ThemeProvider({ children }) {
  const [theme, setTheme] = useState(() => localStorage.getItem('theme') || 'dark')

  useEffect(() => {
    document.documentElement.setAttribute('data-theme', theme)
    document.documentElement.style.colorScheme = theme
    if (theme === 'dark') {
      document.documentElement.classList.add('dark')
    } else {
      document.documentElement.classList.remove('dark')
    }
    localStorage.setItem('theme', theme)
  }, [theme])

  const toggle = useCallback(() => setTheme(t => t === 'dark' ? 'light' : 'dark'), [])
  const value = useMemo(() => ({ theme, toggle }), [theme, toggle])

  return (
    <ThemeContext.Provider value={value}>
      {children}
    </ThemeContext.Provider>
  )
}

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