// Clinical Assistant message translation — local-only via the user's own
// LibreTranslate container. Patient text never leaves the local network.
// Validation failures never retry against anything else.
const crypto = require('crypto');
const axios = require('axios');

const TRANSLATE_PROVIDERS = ['libretranslate'];
const TRANSLATE_LANGS = ['en', 'es', 'fr', 'de', 'it', 'pt', 'zh', 'ar', 'ru', 'hi', 'nl', 'pl', 'tr', 'uk', 'fa', 'sw'];
const MAX_TRANSLATE_CHARS = 20000;
const PROVIDER_TIMEOUT_MS = 15000;
const DEFAULT_CACHE_MAX = 100;
const LANGUAGE_CACHE_MAX = 1;

function failure(message, statusCode, code) {
  return Object.assign(new Error(message), { statusCode, code });
}

function createLanguageCache() {
  return { map: new Map() };
}

function createTranslationCache(max = DEFAULT_CACHE_MAX) {
  return { map: new Map(), max: max };
}

function cacheKey(provider, userId, target, message) {
  const hash = crypto.createHash('sha256').update(String(message)).digest('hex');
  return provider + '\u0000' + String(userId || '') + '\u0000' + target + '\u0000' + hash;
}

function cacheGet(cache, key) { return cache.map.get(key); }

function cacheSet(cache, key, value) {
  if (cache.map.size >= cache.max) cache.map.delete(cache.map.keys().next().value); // ponytail: FIFO eviction is enough here
  cache.map.set(key, value);
}

function isTransientError(err) {
  const status = err && err.response && err.response.status;
  return !status || status >= 500 || status === 429;
}

async function callLibreTranslate(message, target, env, http, format) {
  const base = String(env.LIBRETRANSLATE_URL || 'http://libretranslate:5000');
  if (!/^https?:\/\//.test(base)) throw failure('Local translation service is misconfigured.', 503, 'LIBRETRANSLATE_UNREACHABLE');
  const response = await http.post(base + '/translate', { q: message, source: 'auto', target: target, format: format === 'html' ? 'html' : 'text' }, { timeout: PROVIDER_TIMEOUT_MS });
  const translated = response && response.data && response.data.translatedText;
  if (!translated) throw failure('Local translation service returned no translation.', 502, 'LIBRETRANSLATE_EMPTY');
  return String(translated);
}

async function translateMessage(options) {
  const opts = options || {};
  const message = opts.message;
  const target = String(opts.target || '').toLowerCase();
  const http = opts.axios || axios;
  const env = opts.env || process.env || {};
  var cache = opts.cache || createTranslationCache();
  if (!cache.map) cache = { map: cache, max: DEFAULT_CACHE_MAX }; // accept a raw Map
  if (typeof message !== 'string' || !message.trim()) throw failure('Message to translate is required.', 400, 'INVALID_TRANSLATE');
  if (message.length > MAX_TRANSLATE_CHARS) throw failure('Message exceeds the 20,000 character translation limit.', 400, 'INVALID_TRANSLATE');
  if (!TRANSLATE_LANGS.includes(target)) throw failure('Unsupported translation language.', 400, 'INVALID_TRANSLATE');

  var provider = opts.provider;
  if (opts.provider != null && opts.provider !== '' && !TRANSLATE_PROVIDERS.includes(String(opts.provider).toLowerCase())) {
    throw failure('Unsupported translation provider.', 400, 'INVALID_TRANSLATE_PROVIDER');
  }
  provider = 'libretranslate'; // the only provider — local translation always

  const format = opts.format === 'html' ? 'html' : 'text';
  const key = cacheKey(provider, opts.userId, target, message + '\u0000' + format);
  const hit = cacheGet(cache, key);
  if (hit) return { translated: hit, provider: provider };

  async function run(p) {
    try {
      const translated = await callLibreTranslate(message, target, env, http, format);
      cacheSet(cache, key, translated);
      return { translated, provider: p };
    } catch (err) {
      const error = failure(err && err.message ? err.message : 'Translation service unavailable.',
        (err && err.statusCode) || (isTransientError(err) ? 502 : ((err && err.response && err.response.status) || 502)),
        err && err.code ? err.code : 'TRANSLATION_FAILED');
      error.transient = (isTransientError(err) && !err.statusCode) || err.code === 'LIBRETRANSLATE_EMPTY';
      throw error;
    }
  }

  return run(provider);
}


// Language availability: the local LibreTranslate container only loads a
// subset of models (LT_LOAD_ONLY), so the UI must offer exactly what the
// local instance can actually translate. Cached briefly in-process.

function languagesCacheGet(cache, provider) {
  const hit = cache.map.get(provider);
  if (hit && Date.now() - hit.at < 5 * 60 * 1000) return hit.value;
  return null;
}

function languagesCacheSet(cache, provider, value) {
  cache.map.set(provider, { at: Date.now(), value: value });
}

async function listAvailableLanguages(opts) {
  const provider = String(opts.provider || 'libretranslate').toLowerCase();
  const cache = opts.languageCache || null;
  if (cache) {
    const hit = languagesCacheGet(cache, provider);
    if (hit) return hit;
  }
  const env = opts.env || process.env;
  const http = opts.http || axios;
  if (provider === 'libretranslate') {
    const base = String(env.LIBRETRANSLATE_URL || 'http://libretranslate:5000');
    if (!/^https?:\/\//.test(base)) throw failure('Local translation service is misconfigured.', 503, 'LIBRETRANSLATE_UNREACHABLE');
    let codes;
    try {
      const response = await http.get(base + '/languages', { timeout: 10000 });
      const list = Array.isArray(response && response.data) ? response.data : [];
      codes = list.filter(function(item) { return item && Array.isArray(item.targets) && item.targets.length; }).map(function(item) { return String(item.code).toLowerCase(); });
    } catch (e) {
      if (isTransientError(e)) throw failure('Local translation service is unreachable.', 502, 'LIBRETRANSLATE_UNREACHABLE');
      throw failure('Local translation service rejected the language query.', 502, 'LIBRETRANSLATE_UNREACHABLE');
    }
    if (!codes.length) throw failure('Local translation service returned no languages.', 502, 'LIBRETRANSLATE_EMPTY');
    const value = { libretranslate: codes };
    if (cache) languagesCacheSet(cache, provider, value);
    return value;
  }
  throw failure('Unknown translation provider.', 400, 'INVALID_PROVIDER');
}

module.exports = {
  TRANSLATE_PROVIDERS,
  TRANSLATE_LANGS,
  MAX_TRANSLATE_CHARS,
  createTranslationCache,
  createLanguageCache,
  listAvailableLanguages,
  translateMessage
};