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

type Theme = "dark" | "light";
const ThemeCtx = createContext<{ theme: Theme; toggle: () => void }>({
  theme: "dark",
  toggle: () => {},
});

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setTheme] = useState<Theme>("dark");

  useEffect(() => {
    const stored = (typeof window !== "undefined" && localStorage.getItem("cist-theme")) as Theme | null;
    const initial: Theme = stored ?? "dark";
    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");
      try { localStorage.setItem("cist-theme", next); } catch {}
      return next;
    });
  };

  return <ThemeCtx.Provider value={{ theme, toggle }}>{children}</ThemeCtx.Provider>;
}

export const useTheme = () => useContext(ThemeCtx);