import { createI18n } from "vue-i18n";
import en from "./en.json";
import ru from "./ru.json";
import uk from "./uk.json";

const STORAGE_KEY = "ltt.locale";

export const SUPPORTED_LOCALES = ["en", "ru", "uk"] as const;
export type Locale = (typeof SUPPORTED_LOCALES)[number];

/** Slavic three-form plural: one / few (2-4) / many — shared by ru and uk. */
function slavicPluralRules(choice: number, choicesLength: number): number {
  const mod10 = choice % 10;
  const mod100 = choice % 100;
  if (mod10 === 1 && mod100 !== 11) return 0;
  if (mod10 >= 2 && mod10 <= 4 && (mod100 < 12 || mod100 > 14)) {
    return Math.min(1, choicesLength - 1);
  }
  return choicesLength - 1;
}

function initialLocale(): Locale {
  try {
    const saved = localStorage.getItem(STORAGE_KEY) as Locale | null;
    if (saved && SUPPORTED_LOCALES.includes(saved)) return saved;
  } catch {
    /* storage unavailable */
  }
  const nav = navigator.language.slice(0, 2);
  return SUPPORTED_LOCALES.includes(nav as Locale) ? (nav as Locale) : "en";
}

export const i18n = createI18n({
  legacy: false,
  locale: initialLocale(),
  fallbackLocale: "en",
  messages: { en, ru, uk },
  // vue-i18n's default rule is English-only; without this, Russian and
  // Ukrainian plurals like "1 проекта" come out wrong
  pluralRules: {
    ru: slavicPluralRules,
    uk: slavicPluralRules,
  },
});

export function setLocale(locale: Locale) {
  i18n.global.locale.value = locale;
  try {
    localStorage.setItem(STORAGE_KEY, locale);
  } catch {
    /* storage unavailable */
  }
}