import { useCallback, useEffect, useState } from "react";

type Theme = "light" | "dark";
const STORAGE_KEY = "nanobot-webui.theme";

function readStored(): Theme | null {
  try {
    const v = localStorage.getItem(STORAGE_KEY);
    return v === "light" || v === "dark" ? v : null;
  } catch {
    return null;
  }
}

function applyTheme(theme: Theme): void {
  const root = document.documentElement;
  if (theme === "dark") root.classList.add("dark");
  else root.classList.remove("dark");
}

export function useTheme(): { theme: Theme; toggle: () => void; setTheme: (t: Theme) => void } {
  const [theme, setThemeState] = useState<Theme>(() => {
    const stored = readStored();
    if (stored) return stored;
    if (typeof window !== "undefined" && window.matchMedia) {
      return window.matchMedia("(prefers-color-scheme: dark)").matches
        ? "dark"
        : "light";
    }
    return "light";
  });

  useEffect(() => {
    applyTheme(theme);
    try {
      localStorage.setItem(STORAGE_KEY, theme);
    } catch {
      // ignore
    }
  }, [theme]);

  const setTheme = useCallback((t: Theme) => setThemeState(t), []);
  const toggle = useCallback(
    () => setThemeState((t) => (t === "dark" ? "light" : "dark")),
    [],
  );
  return { theme, toggle, setTheme };
}