/**
 * The page can never stay silently blank.
 *
 * A reader once had nothing but white for an evening: the shell arrived, the
 * modules were served from the browser's own store so not one request reached
 * the hub, and nothing ever rendered. No message, no error on screen, nothing
 * in the server's log to look at — the same account worked in a private window
 * and in another browser, which is the signature of something wrong in this
 * origin's stored state rather than in what was deployed. Clearing the site's
 * data fixed it. Clearing the *cache*, three times, had not: a service worker
 * and IndexedDB are not the cache, and nothing on screen said so.
 *
 * This answers the *silence*, not whatever caused it. A blank page is a bug
 * report nobody can write, and a phone has no console to open.
 *
 * **A classic script, deliberately, and first.** The failure it guards against
 * includes the module graph never linking — one bad module and no module code
 * runs at all, so a guard inside `app.js` would be part of what failed. This
 * one has no imports and cannot be stopped by them.
 *
 * It does nothing when the application mounts, which is the ordinary case: it
 * looks once, late, and speaks only to a reader already staring at nothing.
 */
(function () {
  'use strict';

  // Long enough that a cold phone on a slow network is never interrupted —
  // argon2's wasm, forty modules and a catalogue — and short enough that
  // nobody sits in front of white wondering. The app mounts in well under two
  // seconds when it mounts at all.
  var GIVE_UP_MS = 10000;
  var problems = [];

  function note(what) {
    if (problems.length < 5) problems.push(String(what).slice(0, 200));
  }

  // Capture phase: a `<script>` or stylesheet that fails to load fires `error`
  // at the element, and that one does not bubble.
  window.addEventListener('error', function (e) {
    if (e && e.target && e.target !== window && e.target.src) {
      note('could not load ' + String(e.target.src).replace(/^https?:\/\/[^/]+/, ''));
    } else if (e && e.message) {
      note(e.message);
    }
  }, true);

  window.addEventListener('unhandledrejection', function (e) {
    var r = e && e.reason;
    note((r && (r.message || r)) || 'a promise rejected');
  });

  var FR = (navigator.language || '').toLowerCase().indexOf('fr') === 0;
  var TEXT = FR ? {
    title: 'MeshBay n’a pas pu démarrer',
    body: 'L’application s’est arrêtée avant d’afficher quoi que ce soit. '
        + 'Cela vient presque toujours des données que ce navigateur garde pour ce site.',
    retry: 'Réessayer',
    reset: 'Réinitialiser les données de ce site',
    warn: 'Vous devrez vous reconnecter. Vos fichiers et vos groupes ne sont pas '
        + 'touchés : ils vivent sur les nœuds, pas ici.',
    doing: 'Réinitialisation…',
    blocked: 'Un autre onglet de ce site garde la base ouverte. Fermez les autres '
           + 'onglets meshbay, puis réessayez.',
  } : {
    title: 'MeshBay could not start',
    body: 'The application stopped before it drew anything. This is almost always '
        + 'the data this browser keeps for this site.',
    retry: 'Try again',
    reset: 'Reset this site’s data',
    warn: 'You will have to sign in again. Your files and groups are untouched: '
        + 'they live on the nodes, not here.',
    doing: 'Resetting…',
    blocked: 'Another tab of this site is holding the database open. Close the '
           + 'other meshbay tabs, then try again.',
  };

  /**
   * Deleting a database waits for every connection to it to close, and another
   * tab of this site is a connection. Unwatched, `deleteDatabase` then does
   * nothing at all and says nothing — so this page would reload into the state
   * it had just promised to clear, which is the bug this file exists to end.
   * Blocked deletions are named and handed back.
   */
  function dropDatabase(name) {
    return new Promise(function (res) {
      var req;
      try { req = indexedDB.deleteDatabase(name); } catch (e) { return res(null); }
      var settled = false;
      var end = function (v) { if (!settled) { settled = true; res(v); } };
      req.onsuccess = function () { end(null); };
      req.onerror = function () { end(null); };
      req.onblocked = function () { end(name); };
      setTimeout(function () { end(name); }, 2500);
      return undefined;
    });
  }

  /** Everything this origin holds, and the service worker with it. */
  function resetSiteData(done) {
    var waiting = [];
    var blocked = [];
    try { localStorage.clear(); } catch (e) { /* private mode */ }
    try { sessionStorage.clear(); } catch (e) { /* private mode */ }

    if (window.indexedDB) {
      var names = indexedDB.databases
        ? indexedDB.databases().then(function (dbs) {
            return (dbs || []).map(function (d) { return d && d.name; }).filter(Boolean);
          }).catch(function () { return ['meshbay', 'meshbay_keys']; })
        // Safari and older engines have no `databases()`; these are ours.
        : Promise.resolve(['meshbay', 'meshbay_keys']);
      waiting.push(names.then(function (list) {
        return Promise.all(list.map(dropDatabase)).then(function (results) {
          results.forEach(function (n) { if (n) blocked.push(n); });
        });
      }).catch(function () {}));
    }

    if (window.caches && caches.keys) {
      waiting.push(caches.keys().then(function (keys) {
        return Promise.all((keys || []).map(function (k) { return caches.delete(k); }));
      }).catch(function () {}));
    }

    if (navigator.serviceWorker && navigator.serviceWorker.getRegistrations) {
      waiting.push(navigator.serviceWorker.getRegistrations().then(function (regs) {
        return Promise.all((regs || []).map(function (r) { return r.unregister(); }));
      }).catch(function () {}));
    }

    // Bounded: a hung unregister must not leave the reader on "Resetting…" for
    // ever, which would be this bug wearing a different hat.
    var fired = false;
    var finish = function () { if (!fired) { fired = true; done(blocked); } };
    Promise.all(waiting).then(finish).catch(finish);
    setTimeout(finish, 4000);
  }

  function el(tag, style, text) {
    var n = document.createElement(tag);
    if (style) n.setAttribute('style', style);
    if (text) n.textContent = text;
    return n;
  }

  function show(root) {
    var BTN = 'display:block;width:100%;margin:8px 0;padding:12px 16px;font:inherit;'
            + 'font-size:15px;border-radius:8px;border:1px solid #c9ccd1;background:#fff;'
            + 'color:#111;cursor:pointer';
    var box = el('div', 'max-width:34em;margin:12vh auto;padding:0 20px;'
      + 'font:15px/1.55 system-ui,-apple-system,Segoe UI,Roboto,sans-serif;color:#111');

    box.appendChild(el('h1', 'font-size:20px;margin:0 0 12px', TEXT.title));
    box.appendChild(el('p', 'margin:0 0 16px;color:#444', TEXT.body));

    var retry = el('button', BTN, TEXT.retry);
    retry.addEventListener('click', function () { location.reload(); });
    box.appendChild(retry);

    var reset = el('button', BTN + ';border-color:#b23;color:#b23', TEXT.reset);
    reset.addEventListener('click', function () {
      reset.disabled = true;
      reset.textContent = TEXT.doing;
      resetSiteData(function (blocked) {
        if (!blocked.length) { location.reload(); return; }
        // Reloading here would be a lie: the database is still there, held by
        // another tab, and the page would come back exactly as broken.
        reset.disabled = false;
        reset.textContent = TEXT.reset;
        var why = el('p', 'margin:12px 0 0;color:#b23;font-size:13px',
          TEXT.blocked + ' (' + blocked.join(', ') + ')');
        why.setAttribute('data-blocked', blocked.join(','));
        box.appendChild(why);
      });
    });
    box.appendChild(reset);

    box.appendChild(el('p', 'margin:12px 0 0;color:#666;font-size:13px', TEXT.warn));

    if (problems.length) {
      // Verbatim, and on screen. Nothing else reaches a reader who cannot open
      // a console, and it is the first thing anybody diagnosing this will ask.
      var pre = el('pre', 'margin:16px 0 0;padding:10px;background:#f3f4f6;'
        + 'border-radius:6px;font-size:12px;white-space:pre-wrap;word-break:break-word;'
        + 'color:#333', problems.join('\n'));
      box.appendChild(pre);
    }

    root.appendChild(box);
  }

  setTimeout(function () {
    var root = document.getElementById('app');
    // Mounted, which is the ordinary case and the end of this script's
    // involvement. A later render replaces whatever is here anyway.
    if (!root || root.firstChild) return;
    show(root);
  }, GIVE_UP_MS);
}());