components/theme-toggle.tsx

"use client"

import { useEffect, useState } from "react"
import { useTheme } from "next-themes"
import { Sun, Moon } from "lucide-react"
import { Button } from "@/components/ui/button"

export function ThemeToggle() {
  const { theme, setTheme } = useTheme()
  const [mounted, setMounted] = useState(false)

  useEffect(() => setMounted(true), [])

  const cycleTheme = () => {
    const next = theme === "light" ? "dark" : theme === "dark" ? "system" : "light"
    setTheme(next)
  }

  if (!mounted) return null

  return (
    <Button
      variant="ghost"
      size="icon"
      className="relative"
      onClick={cycleTheme}
      aria-label={`Toggle theme (current: ${theme ?? "system"})`}
    >
      <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" />
    </Button>
  )
}