/**
 * Banner i18n — locale detection and string translation.
 *
 * Loads translations from CDN or uses built-in defaults.
 * Supports string interpolation via {{key}} placeholders.
 */

export interface TranslationStrings {
  title: string;
  description: string;
  acceptAll: string;
  rejectAll: string;
  managePreferences: string;
  savePreferences: string;
  privacyPolicyLink: string;
  closeLabel: string;
  categoryNecessary: string;
  categoryNecessaryDesc: string;
  categoryFunctional: string;
  categoryFunctionalDesc: string;
  categoryAnalytics: string;
  categoryAnalyticsDesc: string;
  categoryMarketing: string;
  categoryMarketingDesc: string;
  categoryPersonalisation: string;
  categoryPersonalisationDesc: string;
  cookieCount: string;
}

/** Built-in English (GB) translations — used as fallback. */
export const DEFAULT_TRANSLATIONS: TranslationStrings = {
  title: 'We use cookies',
  description:
    'We use cookies and similar technologies to enhance your browsing experience, analyse site traffic, and personalise content. You can choose which categories to allow. [Privacy Policy]({{privacy_policy}}) [Terms & Conditions]({{terms}})',
  acceptAll: 'Accept all',
  rejectAll: 'Reject all',
  managePreferences: 'Manage preferences',
  savePreferences: 'Save preferences',
  privacyPolicyLink: 'Privacy Policy',
  closeLabel: 'Close',
  categoryNecessary: 'Necessary',
  categoryNecessaryDesc: 'Essential for the website to function. Always active.',
  categoryFunctional: 'Functional',
  categoryFunctionalDesc: 'Enable enhanced functionality and personalisation.',
  categoryAnalytics: 'Analytics',
  categoryAnalyticsDesc: 'Help us understand how visitors interact with the site.',
  categoryMarketing: 'Marketing',
  categoryMarketingDesc: 'Used to deliver personalised advertisements.',
  categoryPersonalisation: 'Personalisation',
  categoryPersonalisationDesc: 'Enable content personalisation based on your profile.',
  cookieCount: '{{count}} cookies used on this site',
};

/**
 * Detect the user's preferred locale.
 *
 * Priority: 1) explicit data-locale attribute, 2) navigator.language,
 * 3) document lang attribute, 4) 'en'.
 */
export function detectLocale(): string {
  // Check for explicit override on the script tag
  const scriptEl = document.querySelector('script[data-site-id]');
  const explicit = scriptEl?.getAttribute('data-locale');
  if (explicit) return normaliseLocale(explicit);

  // Browser language
  if (typeof navigator !== 'undefined' && navigator.language) {
    return normaliseLocale(navigator.language);
  }

  // Document lang attribute
  const docLang = document.documentElement.lang;
  if (docLang) return normaliseLocale(docLang);

  return 'en';
}

/**
 * Normalise a locale string to a two-letter language code.
 * e.g. 'en-GB' → 'en', 'fr-FR' → 'fr'
 */
export function normaliseLocale(locale: string): string {
  return locale.split('-')[0].toLowerCase();
}

/**
 * Fetch translations for a locale from the CDN.
 * Returns null if not found or on error.
 */
export async function fetchTranslations(
  cdnBase: string,
  locale: string,
): Promise<Partial<TranslationStrings> | null> {
  try {
    const resp = await fetch(`${cdnBase}/translations-${locale}.json`);
    if (!resp.ok) return null;
    return (await resp.json()) as Partial<TranslationStrings>;
  } catch {
    return null;
  }
}

/**
 * Load translations: try fetching from CDN, fall back to defaults.
 */
export async function loadTranslations(
  cdnBase: string,
  locale: string,
): Promise<TranslationStrings> {
  if (locale === 'en') {
    return { ...DEFAULT_TRANSLATIONS };
  }

  const remote = await fetchTranslations(cdnBase, locale);
  if (!remote) {
    return { ...DEFAULT_TRANSLATIONS };
  }

  // Merge remote over defaults so missing keys fall back to English
  return { ...DEFAULT_TRANSLATIONS, ...remote };
}

/**
 * Interpolate placeholders in a translation string.
 * e.g. interpolate('{{count}} cookies', { count: '12' }) → '12 cookies'
 */
export function interpolate(
  template: string,
  values: Record<string, string>,
): string {
  return template.replace(/\{\{(\w+)\}\}/g, (_, key: string) => values[key] ?? '');
}

/**
 * Render markdown-style links as HTML anchor tags and strip orphaned links.
 *
 * Converts `[text](url)` to `<a href="url" ...>text</a>`.
 * If the URL is empty (because the config value wasn't set), the entire
 * `[text]()` fragment is removed so no broken links appear.
 */
export function renderLinks(html: string, linkClass: string = 'consentos-banner__link'): string {
  // Remove links with empty URLs (including surrounding whitespace)
  let result = html.replace(/\s*\[([^\]]*)\]\(\s*\)\s*/g, '');
  // Convert remaining markdown links to <a> tags
  result = result.replace(
    /\[([^\]]+)\]\(([^)]+)\)/g,
    `<a href="$2" target="_blank" rel="noopener" class="${linkClass}">$1</a>`,
  );
  return result;
}