export const LOCALES = ['fr', 'en', 'nl', 'de'] as const;
export type Locale = typeof LOCALES[number];
export const DEFAULT_LOCALE: Locale = 'fr';

export const LOCALE_NAMES: Record<Locale, string> = {
  fr: 'Français',
  en: 'English',
  nl: 'Nederlands',
  de: 'Deutsch',
};

export const LOCALE_HTML_LANG: Record<Locale, string> = {
  fr: 'fr-BE',
  en: 'en',
  nl: 'nl-BE',
  de: 'de',
};

export const LOCALE_OG: Record<Locale, string> = {
  fr: 'fr_BE',
  en: 'en_US',
  nl: 'nl_BE',
  de: 'de_DE',
};

export function isLocale(value: string): value is Locale {
  return (LOCALES as readonly string[]).includes(value);
}

export function detectLocaleFromAcceptLanguage(header: string | null): Locale {
  if (!header) return DEFAULT_LOCALE;
  const parts = header
    .split(',')
    .map((p) => p.split(';')[0].trim().toLowerCase())
    .filter(Boolean);
  for (const part of parts) {
    const short = part.slice(0, 2);
    if (isLocale(short)) return short;
  }
  return DEFAULT_LOCALE;
}