src/contexts/ThemeContext.tsx

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

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

export interface ThemeProviderState {
  theme: Theme;
  setTheme: (theme: Theme) => void;
}

const initialState: ThemeProviderState = {
  theme: "system",
  setTheme: () => null,
};

export const ThemeProviderContext =
  createContext<ThemeProviderState>(initialState);

interface ThemeProviderProps {
  children: ReactNode;
  defaultTheme?: Theme;
  storageKey?: string;
}

export function ThemeProvider({
  children,
  defaultTheme = "system",
  storageKey = "vite-ui-theme",
  ...props
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(
    () => (localStorage.getItem(storageKey) as Theme) || defaultTheme
  );

  useEffect(() => {
    const root = window.document.documentElement;
    root.classList.remove("light", "dark");

    if (theme === "system") {
      const systemTheme = window.matchMedia("(prefers-color-scheme: dark)")
        .matches
        ? "dark"
        : "light";
      root.classList.add(systemTheme);
      return;
    }

    root.classList.add(theme);
  }, [theme]);

  const value = {
    theme,
    setTheme: (newTheme: Theme) => {
      localStorage.setItem(storageKey, newTheme);
      setTheme(newTheme);
    },
  };

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