import { createContext, useContext, useState, useEffect, type ReactNode } from 'react';
import { en, type TextConfig } from '../config/locales/en';
import { de } from '../config/locales/de';
import type { Language } from '../data/types';

const LANGUAGE_STORAGE_KEY = 'preferred-language';

interface LanguageContextType {
  language: Language;
  setLanguage: (lang: Language) => void;
  texts: TextConfig;
}

const LanguageContext = createContext<LanguageContextType | undefined>(undefined);

function normalizeLanguage(value: string | null): Language | null {
  if (value === 'de' || value === 'en') return value;
  return null;
}

function getStoredLanguage(): Language | null {
  try {
    return normalizeLanguage(globalThis.localStorage?.getItem(LANGUAGE_STORAGE_KEY) ?? null);
  } catch {
    return null;
  }
}

function detectBrowserLanguage(): Language {
  const browserLanguage = globalThis.navigator?.language?.toLowerCase() ?? '';
  return browserLanguage.startsWith('en') ? 'en' : 'de';
}

export function detectInitialLanguage(): Language {
  return getStoredLanguage() ?? detectBrowserLanguage();
}

export function LanguageProvider({ initialLanguage, children }: Readonly<{ initialLanguage?: Language; children: ReactNode; }>) {
  const [language, setLanguage] = useState<Language>(initialLanguage ?? detectInitialLanguage());

  const texts = language === 'de' ? de : en;

  const handleSetLanguage = (lang: Language) => {
    setLanguage(lang);
  };

  useEffect(() => {
    document.documentElement.lang = language;
    try {
      globalThis.localStorage?.setItem(LANGUAGE_STORAGE_KEY, language);
    } catch {
      // Ignore storage errors (private mode, denied storage, etc.).
    }
  }, [language]);

  return (
    <LanguageContext.Provider value={{ language, setLanguage: handleSetLanguage, texts }}>
      {children}
    </LanguageContext.Provider>
  );
}

export function useLanguage() {
  const context = useContext(LanguageContext);
  if (context === undefined) {
    throw new Error('useLanguage must be used within a LanguageProvider');
  }
  return context;
}