atc-agents/ui/src/context/ThemeContext.tsx

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

export type Theme = 'light' | 'dark'

type ThemeContextValue = {
  theme: Theme
  toggle: () => void
}

const ThemeContext = createContext<ThemeContextValue | null>(null)
const STORAGE_KEY = 'atc-command-center-theme'

function readStored(): Theme {
  const v = localStorage.getItem(STORAGE_KEY)
  return v === 'dark' || v === 'light' ? v : 'dark'
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<Theme>(() => {
    if (typeof window === 'undefined') return 'dark'
    return readStored()
  })

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

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

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

export function useTheme() {
  const ctx = useContext(ThemeContext)
  if (!ctx) throw new Error('useTheme outside ThemeProvider')
  return ctx
}