'use strict';

// Local copies of the Greatest catalog's cover images. Hotlinking ~100 covers per page
// load makes the image CDN drop some of them at random; one polite download each fixes that.
const fs = require('node:fs');
const path = require('node:path');
const crypto = require('node:crypto');

const TYPES = { 'image/jpeg': '.jpg', 'image/png': '.png', 'image/webp': '.webp', 'image/gif': '.gif', 'image/avif': '.avif' };
const EXTENSIONS = new Set(Object.values(TYPES));
const USER_AGENT = 'MangaCircus-Greatest/1.0';

class GreatestCovers {
  constructor(dir, { fetchImpl = fetch, sleep = ms => new Promise(resolve => setTimeout(resolve, ms)),
    delayMs = 1000, maxBytes = 2 * 1024 * 1024, timeoutMs = 20000 } = {}) {
    this.dir = path.resolve(dir);
    Object.assign(this, { fetchImpl, sleep, delayMs, maxBytes, timeoutMs });
    this.files = new Map(); // key -> file name
    try {
      for (const name of fs.readdirSync(this.dir)) {
        const ext = path.extname(name);
        if (EXTENSIONS.has(ext)) this.files.set(path.basename(name, ext), name);
      }
    } catch (error) { if (error.code !== 'ENOENT') throw error; }
  }
  // A hash of the URL names the file, so a changed catalog URL is fetched again.
  version(url) { return crypto.createHash('sha256').update(String(url)).digest('hex').slice(0, 16); }
  file(url) {
    const name = url ? this.files.get(this.version(url)) : null;
    return name ? path.join(this.dir, name) : null;
  }
  // Sequential, paced, and stops on 403/429 like every other outbound client here.
  async warm(urls) {
    const result = { fetched: 0, skipped: 0, failed: 0, stopped: null };
    let requested = false;
    for (const url of new Set(urls.filter(url => /^https:\/\/\S+$/i.test(String(url || ''))))) {
      if (this.file(url)) { result.skipped++; continue; }
      if (requested) await this.sleep(this.delayMs);
      requested = true;
      try {
        await this.download(url);
        result.fetched++;
      } catch (error) {
        if (error.stop) { result.stopped = error.message; break; }
        result.failed++;
      }
    }
    // Duplicates and repeats of stored covers count as skipped.
    result.skipped += urls.filter(Boolean).length - new Set(urls.filter(Boolean)).size;
    return result;
  }
  async download(url) {
    const response = await this.fetchImpl(url, { headers: { 'user-agent': USER_AGENT },
      signal: AbortSignal.timeout(this.timeoutMs) });
    if ([401, 403, 429].includes(response.status)) throw Object.assign(new Error(`HTTP ${response.status}`), { stop: true });
    if (!response.ok) throw new Error(`HTTP ${response.status}`);
    const ext = TYPES[String(response.headers.get('content-type') || '').split(';')[0].trim().toLowerCase()];
    if (!ext) throw new Error('Not an image');
    if (Number(response.headers.get('content-length')) > this.maxBytes) throw new Error('Image too large');
    const body = Buffer.from(await response.arrayBuffer());
    if (!body.length || body.length > this.maxBytes) throw new Error('Image too large or empty');
    const key = this.version(url), name = key + ext;
    fs.mkdirSync(this.dir, { recursive: true });
    const temp = path.join(this.dir, `.${key}.${crypto.randomBytes(4).toString('hex')}.tmp`);
    try {
      fs.writeFileSync(temp, body);
      fs.renameSync(temp, path.join(this.dir, name));
    } finally { fs.rmSync(temp, { force: true }); }
    this.files.set(key, name);
  }
}

module.exports = { GreatestCovers };