"use client";

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

const STORAGE_KEY = "theme";

export type Theme = "default" | "bbg" | "system";

type ThemeContextValue = {
  theme: Theme;
  setTheme: (theme: Theme) => void;
};

const isTheme = (value: string | null): value is Theme => {
  return value === "default" || value === "bbg" || value === "system";
};

const ThemeContext = createContext<ThemeContextValue | null>(null);

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

  useEffect(() => {
    const stored = localStorage.getItem(STORAGE_KEY);
    if (isTheme(stored)) {
      setTheme(stored);
    } else if (stored !== null && !isTheme(stored)) {
      localStorage.removeItem(STORAGE_KEY);
    }
  }, []);

  useEffect(() => {
    document.documentElement.dataset.theme = theme;
    localStorage.setItem(STORAGE_KEY, theme);
  }, [theme]);

  const value = useMemo<ThemeContextValue>(() => ({ theme, setTheme }), [theme]);

  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
}

export function useTheme(): ThemeContextValue {
  const context = useContext(ThemeContext);
  if (!context) {
    throw new Error("useTheme must be used within a ThemeProvider");
  }
  return context;
}