signal-batch/frontend/src/contexts/ThemeContext.tsx

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

type Theme = 'light' | 'dark'

interface ThemeContextValue {
  theme: Theme
  toggleTheme: () => void
}

export const ThemeContext = createContext<ThemeContextValue>({
  theme: 'light',
  toggleTheme: () => {},
})

const STORAGE_KEY = 'sb-theme'

function getInitialTheme(): Theme {
  const stored = localStorage.getItem(STORAGE_KEY)
  if (stored === 'dark' || stored === 'light') return stored
  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<Theme>(getInitialTheme)

  useEffect(() => {
    document.documentElement.dataset.theme = theme
    localStorage.setItem(STORAGE_KEY, theme)
  }, [theme])

  const toggleTheme = useCallback(() => {
    setTheme(prev => (prev === 'light' ? 'dark' : 'light'))
  }, [])

  return (
    <ThemeContext value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext>
  )
}