src/components/ThemeProvider.tsx

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

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

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

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

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

const ThemeProviderContext = createContext<ThemeProviderState>(initialState);

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);
      root.setAttribute("data-theme", systemTheme);
    } else {
      root.classList.add(theme);
      root.setAttribute("data-theme", theme);
    }
  }, [theme]);

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

  return (
    <ThemeProviderContext.Provider value={value} {...props}>

      {children}

    </ThemeProviderContext.Provider>
  );
}

export const useTheme = () => {
  const context = useContext(ThemeProviderContext);
  
  if (context === undefined)
    throw new Error("useTheme must be used within a ThemeProvider");
  
  return context;
};