open-swe/apps/web/src/components/theme-provider.tsx

"use client";

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

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

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

type 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 = "theme",
  ...props
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(defaultTheme);

  useEffect(() => {
    const savedTheme = localStorage.getItem(storageKey) as Theme | null;
    if (savedTheme) {
      setTheme(savedTheme);
    }
  }, [storageKey]);

  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);
    }
  }, [theme]);

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

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