const fs = require('fs');
const path = require('path');

const CACHE_DIR = process.env.CACHE_DIR || path.join(__dirname, '../../cache');
const MAX_BYTES = 50 * 1024 * 1024;

function ensureDir() {
  if (!fs.existsSync(CACHE_DIR)) fs.mkdirSync(CACHE_DIR, { recursive: true });
}

function cachePath(key) {
  return path.join(CACHE_DIR, key.replace(/[^a-zA-Z0-9._-]/g, '_') + '.json');
}

function get(key, maxAgeMs) {
  ensureDir();
  const p = cachePath(key);
  if (!fs.existsSync(p)) return null;
  try {
    const raw = JSON.parse(fs.readFileSync(p, 'utf8'));
    if (maxAgeMs && Date.now() - raw.fetchedAt > maxAgeMs) return null;
    return raw.data;
  } catch (e) {
    return null;
  }
}

function set(key, data) {
  ensureDir();
  fs.writeFileSync(cachePath(key), JSON.stringify({ fetchedAt: Date.now(), data }, null, 0));
  pruneIfNeeded();
}

function pruneIfNeeded() {
  ensureDir();
  const files = fs.readdirSync(CACHE_DIR).map(f => {
    const p = path.join(CACHE_DIR, f);
    return { p, mtime: fs.statSync(p).mtimeMs, size: fs.statSync(p).size };
  }).sort((a, b) => a.mtime - b.mtime);
  let total = files.reduce((s, f) => s + f.size, 0);
  for (const f of files) {
    if (total <= MAX_BYTES) break;
    fs.unlinkSync(f.p);
    total -= f.size;
  }
}

module.exports = { get, set, CACHE_DIR };