client/src/components/ThemeToggle.tsx

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

export function ThemeToggle() {
  const [theme, setTheme] = useState<"light" | "dark">("light");

  useEffect(() => {
    const stored = localStorage.getItem("theme");
    if (stored === "dark" || (!stored && window.matchMedia("(prefers-color-scheme: dark)").matches)) {
      setTheme("dark");
      document.documentElement.classList.add("dark");
    }
  }, []);

  const toggleTheme = () => {
    const newTheme = theme === "light" ? "dark" : "light";
    setTheme(newTheme);
    localStorage.setItem("theme", newTheme);
    document.documentElement.classList.toggle("dark");
  };

  return (
    <Button
      size="icon"
      variant="ghost"
      onClick={toggleTheme}
      data-testid="button-theme-toggle"
    >
      {theme === "light" ? (
        <Moon className="h-4 w-4" />
      ) : (
        <Sun className="h-4 w-4" />
      )}
    </Button>
  );
}