components/ui/theme-toggle.tsx

'use client'

import * as React from 'react'
import { Moon, Sun } from 'lucide-react'
import { Button } from '@/components/ui/button'

function getPreferredTheme(): 'light' | 'dark' {
  if (typeof window === 'undefined') return 'light'
  const stored = window.localStorage.getItem('theme') as 'light' | 'dark' | null
  if (stored === 'light' || stored === 'dark') return stored
  const prefersDark = window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches
  return prefersDark ? 'dark' : 'light'
}

export function ThemeToggle() {
  const [theme, setTheme] = React.useState<'light' | 'dark'>(() => getPreferredTheme())

  React.useEffect(() => {
    const root = document.documentElement
    if (theme === 'dark') {
      root.classList.add('dark')
    } else {
      root.classList.remove('dark')
    }
    window.localStorage.setItem('theme', theme)
  }, [theme])

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

  return (
    <Button variant="ghost" size="icon" aria-label="Toggle theme" onClick={toggle}>
      <Sun className="h-5 w-5 rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
      <Moon className="absolute h-5 w-5 rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
      <span className="sr-only">Toggle theme</span>
    </Button>
  )
}

export default ThemeToggle