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

type Theme = 'dark' | 'light';

type ThemeProviderProps = {
  // FIX: Made children optional to handle cases where the type checker doesn't correctly infer JSX children.
  children?: ReactNode;
  defaultTheme?: Theme;
  storageKey?: string;
};

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

const initialState: ThemeProviderState = {
  theme: 'light',
  setTheme: () => null,
};

const ThemeProviderContext = createContext<ThemeProviderState>(initialState);

export function ThemeProvider({
  children,
  defaultTheme = 'light',
  storageKey = 'ui-theme',
}: ThemeProviderProps) {
  const [theme, setTheme] = useState<Theme>(() => {
    try {
      const item = window.localStorage.getItem(storageKey);
      if (item) {
        return item as Theme;
      }
      const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
      return prefersDark ? 'dark' : 'light';
    } catch {
      return defaultTheme;
    }
  });

  useEffect(() => {
    const root = window.document.documentElement;

    root.classList.remove('light', 'dark');
    root.classList.add(theme);

    try {
      window.localStorage.setItem(storageKey, theme);
    } catch (e) {
      console.error('Failed to save theme to localStorage', e);
    }
  }, [theme, storageKey]);

  const value = {
    theme,
    setTheme: (newTheme: Theme) => {
      setTheme(newTheme);
    },
  };

  return <ThemeProviderContext.Provider 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;
};