import { useEffect, useState } from "react";

type Theme = "light" | "dark";

function getInitial(): Theme {
  if (typeof window === "undefined") return "light";
  const stored = localStorage.getItem("theme") as Theme | null;
  if (stored === "light" || stored === "dark") return stored;
  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
}

export function useTheme() {
  const [theme, setTheme] = useState<Theme>("light");

  useEffect(() => {
    const initial = getInitial();
    setTheme(initial);
    document.documentElement.classList.toggle("dark", initial === "dark");
  }, []);

  const toggle = () => {
    setTheme((t) => {
      const next: Theme = t === "dark" ? "light" : "dark";
      document.documentElement.classList.toggle("dark", next === "dark");
      localStorage.setItem("theme", next);
      return next;
    });
  };

  return { theme, toggle };
}