// The panel is one page: the header and three views (Машины, Терминал,
// Настройки). Moving between them changes the address without a reload, so
// the terminal view - and every session in it - lives as long as the tab.
// Машины and Настройки come from the server as fragments; their forms are
// sent from here and the fragment drawn again from the answer. A fragment's
// script is a module registered here, mounted on the fragment's root and
// unmounted - its timers, requests and listeners dropped - when it goes.
(function () {
  'use strict';
  const views = {'/': 'machines', '/terminal': 'terminal', '/settings': 'settings'};
  const modules = {};
  const mounted = new Map(); // area -> {mod, scope}
  const $ = s => document.querySelector(s);
  const viewOf = path => views[path] || null;

  function register(name, mod) { modules[name] = mod; }

  // scope gives a module timers, requests and listeners that end with it.
  function scope() {
    const timers = new Set(), offs = [], ac = new AbortController();
    return {
      timeout(fn, ms) { const id = setTimeout(() => { timers.delete(id); fn(); }, ms); timers.add(id); return id; },
      interval(fn, ms) { const id = setInterval(fn, ms); timers.add(id); return id; },
      clear(id) { clearTimeout(id); clearInterval(id); timers.delete(id); },
      fetch(url, opt) {
        const o = Object.assign({credentials: 'same-origin'}, opt || {});
        // A request with its own signal ends on either.
        o.signal = o.signal && AbortSignal.any ? AbortSignal.any([o.signal, ac.signal]) : (o.signal || ac.signal);
        return fetch(url, o);
      },
      on(target, ev, fn, opt) { target.addEventListener(ev, fn, opt); offs.push(() => target.removeEventListener(ev, fn, opt)); },
      signal: ac.signal,
      end() { timers.forEach(id => { clearTimeout(id); clearInterval(id); }); timers.clear(); offs.forEach(f => f()); ac.abort(); }
    };
  }

  function unmount(area) {
    const m = mounted.get(area);
    if (!m) return;
    mounted.delete(area);
    try { if (m.mod.unmount) m.mod.unmount(m.root); } finally { m.scope.end(); }
  }
  function mount(area) {
    const root = area.querySelector('[data-module]');
    const mod = root && modules[root.dataset.module];
    if (!mod) return;
    const sc = scope();
    mounted.set(area, {mod, scope: sc, root});
    mod.mount(root, sc);
  }
  // put draws html in area, the old module unmounted and the new one mounted.
  function put(area, html) {
    unmount(area);
    area.innerHTML = html;
    mount(area);
  }

  const failHTML = msg => '<div class="wrap"><p class="err">' + msg + ' <button type="button" class="btn ghost small" data-retry>Повторить</button></p></div>';
  function withFrag(url) { const u = new URL(url, location.href); u.searchParams.set('frag', '1'); return u; }
  // A request that ended on the sign-in page: the session is over.
  function signedOut(r) { return r.redirected && new URL(r.url).pathname === '/login'; }

  async function load(area, url) {
    let r;
    try { r = await fetch(withFrag(url), {credentials: 'same-origin', cache: 'no-store'}); } catch (e) { r = null; }
    if (r && signedOut(r)) { location.href = '/login'; return; }
    if (!r || !r.ok) {
      put(area, failHTML(r ? 'не загрузилось: ошибка ' + r.status : 'нет связи с сервером'));
      area.querySelector('[data-retry]').onclick = () => load(area, url);
      return;
    }
    put(area, await r.text());
  }

  function show(view) {
    document.querySelectorAll('main#app > .view').forEach(v => { v.hidden = v.dataset.view !== view; });
    document.querySelectorAll('[data-nav]').forEach(a => a.classList.toggle('on', a.dataset.nav === view));
    $('main#app').dataset.view = view;
    document.dispatchEvent(new CustomEvent('app:view', {detail: view}));
  }
  async function go(url, push = true) {
    const u = new URL(url, location.href);
    const view = viewOf(u.pathname);
    if (!view || u.origin !== location.origin) { location.href = u.href; return; }
    if (push && u.pathname + u.search !== location.pathname + location.search) history.pushState({}, '', u.pathname + u.search + u.hash);
    show(view);
    if (view !== 'terminal') await load($('.view[data-view="' + view + '"]'), u.pathname + u.search);
  }

  // Links to a view move to it; any other link behaves as a link.
  document.addEventListener('click', ev => {
    const a = ev.target.closest('a[href]');
    if (!a || ev.defaultPrevented || ev.button !== 0 || ev.metaKey || ev.ctrlKey || ev.shiftKey || a.target || a.hasAttribute('download')) return;
    const u = new URL(a.href, location.href);
    if (u.origin === location.origin && viewOf(u.pathname)) { ev.preventDefault(); go(u.href); }
  });
  window.addEventListener('popstate', () => go(location.href, false));

  // A form in a fragment is sent from here: the answer's address says what
  // to draw. /logout and forms outside the views go the usual way; a form
  // whose onsubmit said no (a confirm) is not sent.
  document.addEventListener('submit', async ev => {
    const f = ev.target;
    const area = f.closest('.view, .frag-area');
    if (!area || ev.defaultPrevented || (f.method || '').toLowerCase() !== 'post' || /\/logout$/.test(f.action)) return;
    ev.preventDefault();
    let r;
    try { r = await fetch(f.action, {method: 'POST', body: new FormData(f), credentials: 'same-origin'}); }
    catch (e) { alert('Нет связи с сервером'); return; }
    if (signedOut(r)) { location.href = '/login'; return; }
    const to = new URL(r.url);
    // From a dialog to a view (a machine deleted): the dialog closes.
    if (!area.classList.contains('view') && viewOf(to.pathname)) {
      const d = area.closest('dialog');
      if (d) d.close();
      go(to.href);
      return;
    }
    if (area.classList.contains('view')) {
      const v = viewOf(to.pathname);
      if (v && v !== area.dataset.view) { go(to.href); return; }
      history.replaceState({}, '', to.pathname + to.search + to.hash);
    }
    // The answer is the page whole (the shell): ask for its fragment.
    await load(area, to.pathname + to.search);
    if (to.hash) { const t = area.querySelector(to.hash); if (t) t.scrollIntoView(); }
  });

  // Leaving the page drops the terminals: the browser asks while one is alive.
  window.addEventListener('beforeunload', ev => {
    if (window.Workspace && window.Workspace.hasLiveSessions()) { ev.preventDefault(); ev.returnValue = ''; }
  });

  // start mounts what the server drew, once every script has registered.
  function start() {
    document.querySelectorAll('main#app > .view').forEach(mount);
    show({dashboard: 'machines', settings: 'settings'}[$('main#app').dataset.view] || 'terminal');
    // /agents/{id}/terminal or /files: that pane, at once.
    const o = window.APP && window.APP.open;
    if (o && window.Workspace) window.Workspace.open(o.kind, o.agent);
  }
  window.App = {go, load, register, put, start, scope};
})();