import type { i18n } from "i18next";
import type { locales } from "@shared/utils/date";
import { unicodeCLDRtoBCP47 } from "@shared/utils/date";
import Desktop from "./Desktop";

/**
 * Formats a number using the user's locale where possible. Use `useFormatNumber` hook
 * instead of this function in React components, to automatically use the user's locale.
 *
 * @param number The number to format
 * @param locale The locale to use for formatting (BCP47 format)
 * @returns The formatted number as a string
 */
export function formatNumber(number: number, locale: string) {
  try {
    return new Intl.NumberFormat(locale).format(number);
  } catch (_err) {
    return number.toString();
  }
}

/**
 * Detects the user's language based on the browser's language settings.
 *
 * @returns The user's language in CLDR format (en_US)
 */
export function detectLanguage() {
  const [ln, r] = navigator.language.split("-");
  const region = (r || ln).toUpperCase();
  return `${ln}_${region}` as keyof typeof locales;
}

/**
 * Changes the language of the app, and updates the spellchecker language
 * if running in the desktop shell.
 *
 * @param locale The locale to change to, in CLDR format (en_US)
 * @param instance The i18n instance to use
 */
export async function changeLanguage(
  locale: string | null | undefined,
  instance: i18n
) {
  // Languages are stored in en_US format in the database, however the
  // frontend translation framework (i18next) expects en-US
  const localeBCP = locale ? unicodeCLDRtoBCP47(locale) : undefined;

  if (localeBCP && instance.languages?.[0] !== localeBCP) {
    await instance.changeLanguage(localeBCP);
    await Desktop.bridge?.setSpellCheckerLanguages(["en-US", localeBCP]);
  }
}

/**
 * Languages with special styling, in ISO 639-1 format.
 */
const scriptsWithLang = new Set([
  "th", // Thai
  "lo", // Lao
  "km", // Khmer
  "my", // Burmese
  "hi", // Hindi
  "mr", // Marathi
  "ne", // Nepali
  "bn", // Bengali
  "gu", // Gujarati
  "pa", // Punjabi
  "te", // Telugu
  "ta", // Tamil
  "ml", // Malayalam
  "si", // Sinhala
  "bo", // Tibetan
  "ar", // Arabic
  "fa", // Persian
  "ur", // Urdu
  "he", // Hebrew
  "am", // Amharic
  "mn", // Mongolian
]);

/**
 * Returns the language code if it requires special text styling, otherwise undefined.
 * This is used to determine if a lang attribute should be set on elements for CSS styling.
 *
 * @param langCode The language code to check, in ISO 639-1 format
 * @returns The language code if it requires special styling, otherwise undefined
 */
export function getLangFor(
  langCode: string | null | undefined
): string | undefined {
  if (!langCode) {
    return undefined;
  }
  return scriptsWithLang.has(langCode) ? langCode : undefined;
}
