"use client";

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

type Theme = "auto" | "light" | "dark";

const ThemeContext = createContext<{
  theme: Theme;
  setTheme: (t: Theme) => void;
}>({ theme: "auto", setTheme: () => {} });

export function useTheme() {
  return useContext(ThemeContext);
}

function applyTheme(theme: Theme) {
  const root = document.documentElement;
  root.classList.remove("light", "dark");
  if (theme === "light") {
    root.classList.add("light");
  } else if (theme === "dark") {
    root.classList.add("dark");
  } else {
    const prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches;
    root.classList.add(prefersDark ? "dark" : "light");
  }
}

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setThemeState] = useState<Theme>("auto");

  useEffect(() => {
    const stored = localStorage.getItem("theme") as Theme | null;
    const initial: Theme =
      stored && ["auto", "light", "dark"].includes(stored) ? stored : "auto";
    setThemeState(initial);
    applyTheme(initial);
  }, []);

  useEffect(() => {
    if (theme !== "auto") return;
    const mq = window.matchMedia("(prefers-color-scheme: dark)");
    const handler = () => applyTheme("auto");
    mq.addEventListener("change", handler);
    return () => mq.removeEventListener("change", handler);
  }, [theme]);

  const setTheme = (t: Theme) => {
    setThemeState(t);
    localStorage.setItem("theme", t);
    applyTheme(t);
  };

  return (
    <ThemeContext.Provider value={{ theme, setTheme }}>
      {children}
    </ThemeContext.Provider>
  );
}