// Post translation for coinos v3: a thin, cached front for a LibreTranslate
// container on the same docker network. Notes are public, so nothing private
// passes through here; the cache keys on the text itself, so a popular post
// is translated once whoever asks.
import { createHash } from 'node:crypto';
import { translatable, translatePieces } from '../src/translate-split.js';

const LT = process.env.LT_URL || 'http://libretranslate:5000';
const MAX_CHARS = 5000;
const CACHE_MAX = 20000;
const BUSY_MAX = 4; // LibreTranslate is CPU-bound: a few at once, the rest wait their turn
const cache = new Map(); // sha256(target|text) -> { text, source }
let busy = 0;
const waiting = [];
let langs = null, langsAt = 0;

async function slot() {
  if (busy < BUSY_MAX) { busy++; return; }
  await new Promise((r) => waiting.push(r));
  busy++;
}
function release() { busy--; const next = waiting.shift(); if (next) next(); }

// The languages the container has models for: { code: [targets] }
export async function languages() {
  if (langs && Date.now() - langsAt < 3600_000) return langs;
  const r = await fetch(LT + '/languages', { signal: AbortSignal.timeout(5000) });
  if (!r.ok) throw new Error('languages ' + r.status);
  const list = await r.json();
  langs = Object.fromEntries(list.map((l) => [l.code, l.targets || []]));
  if (langs['zh-Hans']) langs.zh = langs['zh-Hans']; // the app says 'zh'
  langsAt = Date.now();
  return langs;
}

// The app's locale codes ↔ LibreTranslate's ('zh' is Simplified there).
const norm = (c) => String(c || '').toLowerCase().split(/[-_]/)[0];
const toLt = (c) => (c === 'zh' ? 'zh-Hans' : c);

export async function translate(text, target, source = 'auto') {
  text = String(text || '');
  target = norm(target);
  source = source && source !== 'auto' ? norm(source) : 'auto';
  if (!text.trim()) return { text: '', source };
  if (text.length > MAX_CHARS) throw Object.assign(new Error('too long'), { status: 413 });
  const have = await languages();
  if (!have[toLt(target)]) throw Object.assign(new Error('unsupported language'), { status: 422 });
  const key = createHash('sha256').update(target + '|' + source + '|' + text).digest('hex');
  const hit = cache.get(key);
  if (hit) { cache.delete(key); cache.set(key, hit); return hit; }
  const { prose, tags } = translatable(text, target);
  if (!prose.length && !tags.length) return { text, source: source === 'auto' ? null : source, nothing: true };
  await slot();
  try {
    const call = async (path, body) => {
      const r = await fetch(LT + path, {
        method: 'POST', headers: { 'content-type': 'application/json' },
        body: JSON.stringify(body), signal: AbortSignal.timeout(30_000),
      });
      const out = await r.json().catch(() => ({}));
      if (!r.ok) throw Object.assign(new Error(out.error || path + ' ' + r.status), { status: r.status === 400 ? 422 : 502 });
      return out;
    };
    let from = source, confidence = null;
    if (from === 'auto') {
      const d = await call('/detect', { q: [...prose.map((p) => p.prose), ...tags.map((p) => p.keep.slice(1).replace(/_/g, ' '))].join('\n') });
      from = norm(d[0]?.language) || null;
      confidence = d[0]?.confidence ?? null;
      if (!from) throw Object.assign(new Error('unknown language'), { status: 422 });
    }
    if (from === target) return { text, source: from, confidence };
    if (!have[toLt(from)]) throw Object.assign(new Error('unsupported language'), { status: 422 });
    const translated = await translatePieces(text, async (qs) => {
      const r = await call('/translate', { q: qs, source: toLt(from), target: toLt(target), format: 'text' });
      return Array.isArray(r.translatedText) ? r.translatedText : [r.translatedText];
    }, target);
    const out = { text: translated, source: from, confidence };
    cache.set(key, out);
    if (cache.size > CACHE_MAX) cache.delete(cache.keys().next().value);
    return out;
  } finally { release(); }
}