meshastic.web/src/components/generic/ThemeProvider.tsx

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

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

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

const ThemeContext = createContext<ThemeContextType | undefined>(undefined);

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setTheme] = useState<Theme>(() => {
    if (typeof window !== "undefined") {
      const savedTheme = localStorage.getItem("theme") as Theme;
      return savedTheme || "system";
    }
    return "system";
  });

  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);
    } else {
      root.classList.add(theme);
    }

    localStorage.setItem("theme", theme);
  }, [theme]);

  useEffect(() => {
    const mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");

    const handleChange = () => {
      if (theme === "system") {
        const root = window.document.documentElement;
        root.classList.remove("light", "dark");
        root.classList.add(mediaQuery.matches ? "dark" : "light");
      }
    };

    mediaQuery.addEventListener("change", handleChange);
    return () => mediaQuery.removeEventListener("change", handleChange);
  }, [theme]);

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

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