// Soft navigation. Same-app links and form posts are fetched and swapped into the page in place,
// so a button press no longer reloads the whole document. Progressive enhancement: without this
// script (or on any failure) the browser's own navigation runs. Forms marked `data-hard` (sign-in,
// sign-out, enrolment, password and account changes) always post natively.
(function () {
  'use strict';
  if (window.__forgeSoft) { return; }
  window.__forgeSoft = true;

  var root = document.documentElement;
  var latest = 0;                 // id of the newest request; older responses are dropped
  var inFlight = 0;               // requests on the wire, drives aria-busy
  var pending = new WeakSet();    // forms with a request on the wire: a second submit is ignored
  var shown = location.pathname + location.search;
  var GET_INIT = { headers: { accept: 'text/html' } };

  // Files, not pages: static assets, the JSON api, archives, raw and LFS objects and release
  // downloads. These always take the browser's own path.
  var FILE_PATH = /^\/(assets|api)\/|^\/[^\/]+\/[^\/]+\/(archive|raw|info\/lfs|-\/media|releases\/download)(\/|$)/;

  function busyStart() {
    inFlight += 1;
    root.setAttribute('aria-busy', 'true');
  }

  function busyEnd() {
    inFlight = Math.max(0, inFlight - 1);
    if (inFlight === 0) { root.removeAttribute('aria-busy'); }
  }

  // The URL to fetch for `href`, or null when the browser should handle it: another origin, a file
  // route, or a value that does not parse.
  function pageUrl(href) {
    var url;
    try { url = new URL(href, location.href); } catch (err) { return null; }
    if (url.origin !== location.origin || FILE_PATH.test(url.pathname)) { return null; }
    return url;
  }

  function withoutHash(url) {
    var out = new URL(url.href);
    out.hash = '';
    return out;
  }

  // Field preservation: a dirty or focused field keeps its value, and the caret offsets come along.
  function fieldKey(el) {
    var form = el.form ? (el.form.getAttribute('action') || '') : '';
    return form + '|' + (el.name || '') + '|' + (el.type || '') + '|' + el.tagName;
  }

  function savable(el) {
    return el.type !== 'hidden' && el.type !== 'password' && el.type !== 'file';
  }

  function captureFields() {
    var active = document.activeElement;
    var out = [];
    document.querySelectorAll('input, textarea, select').forEach(function (el) {
      if (!savable(el)) { return; }
      var moved;
      if (el.type === 'checkbox' || el.type === 'radio') {
        moved = el.checked !== el.defaultChecked;
      } else if (el.tagName === 'SELECT') {
        var def = -1;
        for (var j = 0; j < el.options.length; j++) {
          if (el.options[j].defaultSelected) { def = j; break; }
        }
        if (def < 0) { def = 0; }
        moved = el.selectedIndex !== def;
      } else {
        moved = el.value !== el.defaultValue;
      }
      var focused = el === active;
      if (!moved && !focused) { return; }
      var start = -1, end = -1;
      try {
        if (el.selectionStart != null) { start = el.selectionStart; end = el.selectionEnd; }
      } catch (err) { }
      out.push({ k: fieldKey(el), v: el.value, c: el.checked, i: el.selectedIndex, f: focused, s: start, e: end });
    });
    return out;
  }

  function restoreFields(saved) {
    if (!saved || !saved.length) { return; }
    var fields = document.querySelectorAll('input, textarea, select');
    saved.forEach(function (was) {
      var el = null;
      for (var i = 0; i < fields.length; i++) {
        if (fieldKey(fields[i]) === was.k) { el = fields[i]; break; }
      }
      if (!el) { return; }
      if (el.type === 'checkbox' || el.type === 'radio') { el.checked = was.c; }
      else if (el.tagName === 'SELECT') { el.selectedIndex = was.i; }
      else { el.value = was.v; }
      if (was.f) {
        try {
          el.focus({ preventScroll: true });
          if (was.s >= 0 && el.setSelectionRange) { el.setSelectionRange(was.s, was.e); }
        } catch (err) { }
      }
    });
  }

  // Stylesheets in <head> follow the new page: missing ones are added, extra ones removed. Matched by
  // href, so main.css and the highlight sheet stay in place when they are the same.
  function syncStyles(doc) {
    var sheets = 'link[rel="stylesheet"]';
    var wanted = {};
    doc.head.querySelectorAll(sheets).forEach(function (l) { wanted[l.getAttribute('href') || ''] = true; });
    var have = {};
    document.head.querySelectorAll(sheets).forEach(function (l) { have[l.getAttribute('href') || ''] = true; });
    doc.head.querySelectorAll(sheets).forEach(function (l) {
      var href = l.getAttribute('href') || '';
      if (!have[href]) {
        have[href] = true;
        document.head.appendChild(document.importNode(l, true));
      }
    });
    document.head.querySelectorAll(sheets).forEach(function (l) {
      if (!wanted[l.getAttribute('href') || '']) { l.remove(); }
    });
  }

  function adopt(doc, keepFields) {
    document.title = doc.title;
    ['lang', 'data-theme', 'data-ui'].forEach(function (name) {
      if (doc.documentElement.hasAttribute(name)) { root.setAttribute(name, doc.documentElement.getAttribute(name)); }
      else { root.removeAttribute(name); }
    });
    syncStyles(doc);
    var kept = keepFields ? captureFields() : null;
    var nodes = Array.prototype.map.call(doc.body.childNodes, function (n) { return document.importNode(n, true); });
    document.body.replaceChildren.apply(document.body, nodes);
    // Re-create scripts so they run (a parsed-in script does not). The guard above keeps this file
    // from starting twice.
    document.body.querySelectorAll('script').forEach(function (old) {
      var s = document.createElement('script');
      Array.prototype.forEach.call(old.attributes, function (a) { s.setAttribute(a.name, a.value); });
      s.textContent = old.textContent;
      old.replaceWith(s);
    });
    if (kept) { restoreFields(kept); }
  }

  function focusMain() {
    var main = document.querySelector('main');
    if (main && main.focus) { main.focus({ preventScroll: true }); }
  }

  // Scrolls to the fragment's element when there is one. Returns false when there is nothing to scroll to.
  function placeHash(hash) {
    if (!hash || hash.length < 2) { return false; }
    var id;
    try { id = decodeURIComponent(hash.slice(1)); } catch (err) { id = hash.slice(1); }
    var el = document.getElementById(id);
    if (!el) { return false; }
    el.scrollIntoView();
    return true;
  }

  // how: 'nav' (link or GET form: push, top), 'pop' (history: push nothing, restore scroll),
  // 'post' (form post: replace, keep scroll), 'query' (in place: replace, keep scroll).
  function swap(html, dest, how, keepFields) {
    var doc = new DOMParser().parseFromString(html, 'text/html');
    if (!doc.body) { location.assign(dest.href); return; }
    var x = window.scrollX, y = window.scrollY;
    var saved = history.state;
    adopt(doc, keepFields);
    if (how === 'nav') { history.pushState(null, '', dest.href); }
    else if (how === 'post' || how === 'query') { history.replaceState(null, '', dest.href); }
    shown = dest.pathname + dest.search;
    if (how === 'nav' || how === 'pop') { focusMain(); }
    if (placeHash(dest.hash)) { return; }
    if (how === 'post' || how === 'query') { window.scrollTo(x, y); }
    else if (how === 'pop') { window.scrollTo(0, saved && typeof saved.y === 'number' ? saved.y : 0); }
    else { window.scrollTo(0, 0); }
  }

  // The browser takes over where a soft request cannot: a non-HTML answer, or another origin.
  // A GET re-requests the page itself. A POST is never sent again (that would repeat the action):
  // a redirect is followed as a GET, anything else reloads the current page.
  function leave(res, o) {
    if (o.post) {
      if (res.redirected) { location.assign(res.url.href); } else { location.reload(); }
      return;
    }
    var sameOrigin = res.url.origin === location.origin;
    location.assign(sameOrigin && !res.redirected ? o.dest.href : res.url.href);
  }

  // One request for a page. `o` carries target (fetched, no hash), dest (shown, with hash), init,
  // how, keep (keep fields on a re-render of the same path), post, and the form for a POST or GET form.
  function load(o) {
    var mark = ++latest;
    busyStart();
    fetch(o.target.href, o.init).then(function (r) {
      var final = new URL(r.url || o.target.href);
      var html = /^\s*text\/html/i.test(r.headers.get('content-type') || '');
      if (final.origin !== location.origin || !html) {
        return { leave: true, url: final, redirected: r.redirected };
      }
      return r.text().then(function (text) { return { html: text, url: final }; });
    }).then(function (res) {
      if (mark !== latest) { return; }
      if (res.leave) { leave(res, o); return; }
      var dest = new URL(res.url.href);
      dest.hash = o.dest.hash;
      swap(res.html, dest, o.how, !!o.keep && res.url.pathname === o.target.pathname);
    }).catch(function () {
      if (mark !== latest) { return; }
      if (o.post) { o.form.submit(); } else { location.assign(o.dest.href); }
    }).then(function () {
      busyEnd();
      if (o.form) { pending.delete(o.form); }
    });
  }

  function saveScroll() {
    try { history.replaceState({ y: window.scrollY }, '', location.href); } catch (err) { }
  }

  document.addEventListener('click', function (e) {
    if (e.defaultPrevented || e.button !== 0 || e.metaKey || e.ctrlKey || e.shiftKey || e.altKey) { return; }
    var a = e.target && e.target.closest ? e.target.closest('a[href]') : null;
    if (!a || a.target || a.hasAttribute('download') || a.hasAttribute('data-hard')) { return; }
    var href = a.getAttribute('href') || '';
    // Same-app paths only: `//host` is protocol-relative, another origin, and goes the browser's way.
    if (href.charAt(0) !== '/' || href.charAt(1) === '/') { return; }
    var url = pageUrl(href);
    if (!url) { return; }
    // A fragment on the page already shown: the browser scrolls by itself.
    if (url.pathname + url.search === shown && url.hash) { return; }
    e.preventDefault();
    saveScroll();
    load({ target: withoutHash(url), dest: url, init: GET_INIT, how: 'nav', keep: false, post: false, form: null });
  }, true);

  document.addEventListener('submit', function (e) {
    var form = e.target;
    if (!form || form.tagName !== 'FORM' || form.hasAttribute('data-hard') || form.getAttribute('target')) { return; }
    var submitter = e.submitter || null;
    // Per-button overrides other than the action are rare: the browser handles those.
    if (submitter && (submitter.hasAttribute('formmethod') || submitter.hasAttribute('formenctype') ||
        submitter.hasAttribute('formtarget') || submitter.hasAttribute('data-hard'))) { return; }
    var action = (submitter && submitter.getAttribute('formaction')) || form.getAttribute('action') || location.href;
    var url = pageUrl(action);
    if (!url) { return; }
    e.preventDefault();
    if (pending.has(form)) { return; }
    pending.add(form);

    var data = new FormData(form);
    if (submitter && submitter.name) { data.append(submitter.name, submitter.value); }
    var method = (form.getAttribute('method') || 'get').toLowerCase();

    if (method === 'get') {
      var q = new URLSearchParams(data).toString();
      var dest = withoutHash(url);
      dest.search = q ? '?' + q : '';
      saveScroll();
      load({ target: dest, dest: dest, init: GET_INIT, how: 'nav', keep: false, post: false, form: form });
      return;
    }

    var multipart = (form.enctype || '').toLowerCase().indexOf('multipart') === 0;
    load({
      target: withoutHash(url),
      dest: url,
      init: {
        method: 'POST',
        headers: { accept: 'text/html' },
        body: multipart ? data : new URLSearchParams(data)
      },
      how: 'post',
      keep: true,
      post: true,
      form: form
    });
  }, false);

  window.addEventListener('popstate', function () {
    var here = location.pathname + location.search;
    if (here === shown) { placeHash(location.hash); return; }
    var url = pageUrl(location.href);
    if (!url) { location.reload(); return; }
    load({ target: withoutHash(url), dest: url, init: GET_INIT, how: 'pop', keep: false, post: false, form: null });
  });

  // Filter controls submit their form on change.
  document.addEventListener('change', function (e) {
    var c = e.target && e.target.closest ? e.target.closest('[data-autosubmit]') : null;
    if (!c || !c.form) { return; }
    if (c.form.requestSubmit) { c.form.requestSubmit(); } else { c.form.submit(); }
  });

  // A filtered view asked for in place: the URL is replaced (no history entry per change), fields
  // and caret come through the swap, and the scroll stays put.
  window.__forgeQuery = function (href) {
    var url = pageUrl(href);
    if (!url) { location.assign(href); return; }
    load({ target: withoutHash(url), dest: url, init: GET_INIT, how: 'query', keep: true, post: false, form: null });
  };
})();