"use client";

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

const STORAGE_KEY = "theme";

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

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

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

export function ThemeProvider({ children }: { children: ReactNode }) {
  const [theme, setThemeState] = useState<Theme>("light");
  const [mounted, setMounted] = useState(false);

  useEffect(() => {
    setMounted(true);
    const hasDark = document.documentElement.classList.contains("dark");
    setThemeState(hasDark ? "dark" : "light");
  }, []);

  useEffect(() => {
    if (!mounted) return;
    const root = document.documentElement;
    if (theme === "dark") {
      root.classList.add("dark");
    } else {
      root.classList.remove("dark");
    }
    localStorage.setItem(STORAGE_KEY, theme);
  }, [theme, mounted]);

  const setTheme = useCallback((newTheme: Theme) => {
    setThemeState(newTheme);
  }, []);

  const toggleTheme = useCallback(() => {
    setThemeState((prev) => (prev === "light" ? "dark" : "light"));
  }, []);

  const value: ThemeContextValue = {
    theme,
    setTheme,
    toggleTheme,
  };

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

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