// Tiny reactive i18n for the SPA (vue-i18n is deliberately not pulled in):
// a locale ref, a t() with {param} interpolation and Slavic plural forms,
// and flat per-area message dictionaries. The default locale is set from
// the backend's locale_effective (settings override -> auth account -> en).
import { ref, watch } from "vue";

import en from "./messages/en.js";
import uk from "./messages/uk.js";
import ru from "./messages/ru.js";

const messages = { en, uk, ru };

// Language tags normalize to their 2-letter prefix ("en-US" -> "en");
// anything the dictionaries don't ship falls back to English.
export const SUPPORTED_LOCALES = Object.keys(messages);

export const locale = ref("en");

function normalizeTag(tag) {
  const prefix = String(tag || "").trim().toLowerCase().split(/[-_]/)[0];
  return messages[prefix] ? prefix : null;
}

export function setLocale(tag) {
  locale.value = normalizeTag(tag) || "en";
}

watch(locale, (lang) => {
  if (typeof document !== "undefined") {
    document.documentElement.lang = lang;
  }
});

function pluralCategory(lang, n) {
  // ru/uk: n%10==1 (except 11) -> one; 2-4 (except 12-14) -> few; else many
  const mod10 = n % 10;
  const mod100 = n % 100;
  if (lang === "ru" || lang === "uk") {
    if (mod10 === 1 && mod100 !== 11) return "one";
    if (mod10 >= 2 && mod10 <= 4 && !(mod100 >= 12 && mod100 <= 14)) return "few";
    return "many";
  }
  return n === 1 ? "one" : "other";
}

function interpolate(text, params) {
  return text.replace(/\{(\w+)\}/g, (match, key) =>
    params && key in params ? String(params[key]) : match
  );
}

function lookup(slug) {
  return messages[locale.value]?.[slug] ?? messages.en[slug];
}

export function t(slug, params) {
  let text = lookup(slug);
  if (text != null && typeof text === "object") {
    // plural dictionary {one, few, many, other}; a missing form falls to other
    const n = Number(params?.n ?? 0);
    text = text[pluralCategory(locale.value, n)] ?? text.other;
  }
  return text != null ? interpolate(String(text), params) : slug;
}