const { fetchJson, clampPage, isRetryable } = require('./http');

const PAGE_SIZE = 30;
const CATALOG_START = '2000-01-01';
const SNAPSHOT_TTL = 5 * 60 * 1000;
let catalogSnapshot = null;

function toItem(r, server) {
  const authors = String(r.authors || '').split(';').map((s) => s.trim()).filter(Boolean).slice(0, 3).join(', ');
  return {
    postId: r.doi,
    title: r.title || '(无标题)',
    cover: '',
    date: r.date || '',
    url: `https://www.${server}.org/content/${r.doi}v${r.version || 1}`,
    subtitle: [authors, r.category].filter(Boolean).join(' · '),
    _server: server
  };
}

function dateStr(d) { return d.toISOString().slice(0, 10); }

async function fetchWindow(server, from, to, cursor, tries = 3) {
  let last;
  for (let i = 0; i < tries; i++) {
    try {
      const j = await fetchJson(`https://api.biorxiv.org/details/${server}/${from}/${to}/${cursor}`, { retries: 0 });
      const total = parseInt(j.messages && j.messages[0] && j.messages[0].total, 10) || 0;
      return { total, collection: j.collection || [] };
    } catch (e) {
      last = e;
      // 超时与网络抖动是这里最常见的瞬时故障，必须一并重试
      if (!isRetryable(e) || i === tries - 1) throw e;
      await new Promise((r) => setTimeout(r, 1500 * (i + 1)));
    }
  }
  throw last;
}

module.exports = {
  id: 'biorxiv',
  name: 'bioRxiv 预印本',
  supportsSearch: false,

  async list(page) {
    page = clampPage(page);
    const server = 'biorxiv';
    const to = dateStr(new Date());
    if (!catalogSnapshot || catalogSnapshot.to !== to || catalogSnapshot.expiresAt <= Date.now()) {
      const first = await fetchWindow(server, CATALOG_START, to, 0);
      catalogSnapshot = { to, total: first.total, expiresAt: Date.now() + SNAPSHOT_TTL };
    }
    const total = catalogSnapshot.total;
    const end = Math.max(0, total - (page - 1) * PAGE_SIZE);
    const cursor = Math.max(0, end - PAGE_SIZE);
    const count = end - cursor;
    if (!count) return { items: [], maxPage: Math.max(1, Math.ceil(total / PAGE_SIZE)), page };
    const { collection } = await fetchWindow(server, CATALOG_START, to, cursor);
    const items = collection.slice(0, count).reverse().map((r) => toItem(r, server));
    return { items, maxPage: Math.max(1, Math.ceil(total / PAGE_SIZE)), page };
  },

  async search() {
    throw new Error('bioRxiv 暂不支持搜索，请翻页浏览');
  },

  async detail(postId) {
    const j = await fetchJson(`https://api.biorxiv.org/details/biorxiv/${postId}`);
    const c = (j.collection || [])[0];
    if (!c) throw new Error('未找到该预印本');
    return {
      postId,
      title: c.title,
      cover: '',
      authors: String(c.authors || '').split(';').map((s) => s.trim()).filter(Boolean),
      date: c.date || '',
      tags: [c.category ? `分类：${c.category}` : '', c.license ? `许可：${c.license}` : ''].filter(Boolean),
      brief: c.abstract || '',
      url: `https://www.biorxiv.org/content/${c.doi}v${c.version || 1}`,
      links: [{ name: 'bioRxiv 页', url: `https://www.biorxiv.org/content/${c.doi}v${c.version || 1}` }]
    };
  },

  async download(postId) {
    const j = await fetchJson(`https://api.biorxiv.org/details/biorxiv/${postId}`);
    const c = (j.collection || [])[0];
    const v = (c && c.version) || 1;
    return {
      files: [{ name: `${String(postId).replace(/\//g, '_')}.pdf`, link: `https://www.biorxiv.org/content/${postId}v${v}.full.pdf`, format: 'PDF' }],
      links: [{ name: 'bioRxiv 页', url: `https://www.biorxiv.org/content/${postId}v${v}` }]
    };
  }
};