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

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

interface ThemeContextValue {
  theme: Theme
  resolved: 'light' | 'dark'
  setTheme: (t: Theme) => void
}

const ThemeContext = createContext<ThemeContextValue | null>(null)

const STORAGE_KEY = 'sundynix-theme'

function systemTheme(): 'light' | 'dark' {
  return window.matchMedia('(prefers-color-scheme: dark)').matches
    ? 'dark'
    : 'light'
}

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>(
    () => (localStorage.getItem(STORAGE_KEY) as Theme) ?? 'system',
  )
  const [resolved, setResolved] = useState<'light' | 'dark'>(() =>
    theme === 'system' ? systemTheme() : theme,
  )

  useEffect(() => {
    const apply = () => {
      const r = theme === 'system' ? systemTheme() : theme
      setResolved(r)
      document.documentElement.classList.toggle('dark', r === 'dark')
    }
    apply()
    const mq = window.matchMedia('(prefers-color-scheme: dark)')
    mq.addEventListener('change', apply)
    return () => mq.removeEventListener('change', apply)
  }, [theme])

  const setTheme = (t: Theme) => {
    localStorage.setItem(STORAGE_KEY, t)
    setThemeState(t)
  }

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

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