/* Sequential library loader with retry.
 *
 * The page is served over a Tailscale Funnel, which occasionally returns a
 * transient 502 on a cold connection. With plain <script> tags a single
 * hiccup leaves `cornerstone` undefined and the whole viewer dies with a
 * black screen — unacceptable when the person on the other end is a doctor
 * who cannot open a console. Loading in order, with retries, and only then
 * starting the app, turns that into a non-event.
 */
'use strict';

const LIBS = [
  'lib/hammer.min.js',
  'lib/dicomParser.min.js',
  'lib/cornerstone.min.js',
  'lib/cornerstoneMath.min.js',
  'lib/cornerstoneTools.min.js',
  'lib/cornerstoneWADOImageLoader.bundle.min.js',
];

const status = document.getElementById('loader');
const setStatus = t => { if (status) status.textContent = t; };

function loadScript(src, attempts) {
  attempts = attempts || 4;
  return new Promise((resolve, reject) => {
    const attempt = n => {
      const s = document.createElement('script');
      // cache-bust on retry so a failed/cached-empty response is not reused
      s.src = n === 1 ? src : src + (src.indexOf('?') === -1 ? '?' : '&') + 'retry=' + n;
      s.async = false;
      s.onload = () => resolve(src);
      s.onerror = () => {
        s.remove();
        if (n < attempts) {
          setStatus(`组件加载失败,正在重试(${n}/${attempts - 1})…`);
          setTimeout(() => attempt(n + 1), 700 * n);
        } else {
          reject(new Error('无法加载 ' + src));
        }
      };
      document.head.appendChild(s);
    };
    attempt(1);
  });
}

(async () => {
  try {
    for (let i = 0; i < LIBS.length; i++) {
      setStatus(`正在加载组件 ${i + 1}/${LIBS.length} …`);
      await loadScript(LIBS[i]);
    }
    setStatus('正在启动查看器…');
    await loadScript('app.js');
  } catch (err) {
    const bar = document.getElementById('errorBar');
    if (bar) {
      bar.hidden = false;
      bar.textContent = '加载失败: ' + err.message +
        '\n请刷新页面重试;若持续失败,请确认本机影像服务是否仍在运行。';
    }
    setStatus('加载失败');
  }
})();