src/boot-template.js

/* One template page (template.html) — external module so the page can ship a
 * strict CSP, same as index.html.
 *
 * The engine is created but not started. createTemplate() calls startPyrel()
 * on the first Run, so reading the notebook costs one 40 KB document rather
 * than ~100 MB of WebAssembly.
 */
import { createTemplate } from './template.js';
import { createEngine, engineModeFromLocation } from './engine/engine.js';
import { showBootError } from './boot-error.js';

try {
  const slug = new URLSearchParams(location.search).get('t');
  if (!slug) throw new Error('no template named — open this page from templates.html');
  // Slug comes from the URL and is used to build a fetch path, so it is checked
  // against the shape the extractor emits rather than trusted.
  if (!/^[a-z0-9][a-z0-9_-]*$/i.test(slug)) throw new Error(`not a template name: ${slug}`);

  const res = await fetch(`data/templates/${slug}.json`);
  if (!res.ok) throw new Error(`no template "${slug}" — ${res.status} ${res.statusText}`);
  const doc = await res.json();
  document.title = `${doc.title} — Templates — Event Horizon`;

  /* wasm by default, not `auto`.
   *
   * `auto` prefers wasm but probes the sidecar on the way, which on a static
   * host is a request that cannot succeed — a 502 in the console of a page that
   * is working fine. And the fallback is pointless here: templates need
   * prepareTemplate, which only the browser engine has, so falling through to
   * the sidecar can only turn a slow start into "the server engine cannot run
   * templates". ?engine=server still reaches it, and still says that.
   *
   * It is also the honest default for what this page claims. "Runs right here,
   * in this tab" should not quietly be served by a process somewhere else. */
  const engine = createEngine({
    mode: new URLSearchParams(location.search).get('engine') ? engineModeFromLocation() : 'wasm',
    onProgress: (text) => {
      const p = document.querySelector('[data-el="progress"]');
      if (p) p.textContent = text;
    },
  });
  window.template = createTemplate({ doc, engine });
} catch (e) {
  showBootError(e);
}