/* Autosave, unsaved-work guard and draft recovery — S2 / T4.3.
   ---------------------------------------------------------------------------
   The work package form is roughly 4,700px tall and there was no autosave and no
   unsaved-work guard on it. The only beforeunload listener in the app was
   analytics dwell tracking (work-package-suite-app.js), so a mis-click, a closed
   tab or a crash lost everything typed since the last explicit Save.

   Three separate things, often confused:

     THE DRAFT      what you have typed, saved here, locally, continuously.
     THE RECORD     what you have explicitly Saved, which goes to the server.
     THE OUTBOX     project-data.js, which gets the RECORD to the server reliably.

   This file owns the first only. It never writes to the server: a draft is
   "unfinished work this browser is holding for you", and pushing unfinished work
   to a shared project is a different feature with different consequences.

   The guard fires only when the form actually differs from the record. A dialog
   that appears on every exit gets clicked through within a day and is worse than
   no dialog, which is why `Do not: fire the guard when nothing has changed` is
   part of the task rather than a nicety.
*/
(function (window, document) {
  'use strict';

  var DRAFT_PREFIX = 'wp_draft::';
  var DEBOUNCE_MS = 1200;

  var reg = null;           // the single registered surface for this page
  var timer = null;
  var status = { state: 'idle', at: null, error: null };
  var statusSubs = [];
  var guardInstalled = false;

  function now() { return new Date().toISOString(); }

  function emit() {
    statusSubs.forEach(function (fn) {
      try { fn(Object.assign({}, status), reg ? reg.isDirty() : false); } catch (e) {}
    });
  }

  function setStatus(state, extra) {
    status = Object.assign({ state: state, at: status.at, error: null }, extra || {});
    emit();
  }

  function draftKey(id) { return DRAFT_PREFIX + id; }

  function readDraft(id) {
    try { return JSON.parse(window.localStorage.getItem(draftKey(id)) || 'null'); }
    catch (e) { return null; }
  }

  function writeDraft(id, payload) {
    // A failed write is the one case that MUST be surfaced rather than swallowed:
    // it means the safety net is not there, and the user is the only one who can
    // act on that (close a tab, free some quota, save explicitly now).
    window.localStorage.setItem(draftKey(id), JSON.stringify(payload));
  }

  function clearDraft(id) {
    try { window.localStorage.removeItem(draftKey(id)); } catch (e) {}
  }

  function save(reason) {
    if (!reg) return false;
    if (!reg.isDirty()) { setStatus('idle'); return false; }
    setStatus('saving');
    try {
      writeDraft(reg.draftId(), {
        v: 1, at: now(), reason: reason || 'debounce',
        entity: reg.id, data: reg.collect(),
      });
      setStatus('saved', { at: now() });
      return true;
    } catch (e) {
      // QuotaExceededError, private-mode storage, a locked profile.
      setStatus('failed', { error: (e && e.message) || String(e) });
      return false;
    }
  }

  function schedule(reason) {
    if (!reg) return;
    clearTimeout(timer);
    timer = setTimeout(function () { save(reason || 'debounce'); }, DEBOUNCE_MS);
  }

  function installGuard() {
    if (guardInstalled) return;
    guardInstalled = true;
    // ADDED alongside the analytics dwell listener, never replacing it. Both fire;
    // beforeunload supports multiple listeners and the analytics one does not
    // preventDefault, so the two do not interact.
    window.addEventListener('beforeunload', function (e) {
      if (!reg || !reg.isDirty()) return undefined;   // nothing unsaved: stay silent
      save('unload');                                 // one last draft write
      e.preventDefault();
      e.returnValue = '';                             // required by Chrome
      return '';
    });
    // A crash or a killed tab never fires beforeunload. `visibilitychange` to
    // hidden does, and it is the last reliable moment to write the draft - which
    // is what makes the recovery survive "kill the tab and reopen".
    document.addEventListener('visibilitychange', function () {
      if (document.visibilityState === 'hidden') save('hidden');
    });
  }

  window.WPAutosave = {
    /* Register the page's editable surface.

         id        stable name for the surface, e.g. 'wp-form'
         scope     element to watch for input/change (defaults to document)
         draftId   () => storage id, usually project + entity so two projects do
                   not share one draft
         collect   () => a JSON-serialisable snapshot of the form
         isDirty   () => does the form differ from the last explicitly saved record
         restore   (data) => put a recovered snapshot back into the form
    */
    register: function (opts) {
      reg = {
        id: opts.id,
        scope: opts.scope || document,
        draftId: opts.draftId || function () { return opts.id; },
        collect: opts.collect,
        isDirty: opts.isDirty,
        restore: opts.restore,
      };
      reg.scope.addEventListener('input', function () { schedule('input'); });
      reg.scope.addEventListener('change', function () { schedule('change'); });
      installGuard();
      return window.WPAutosave;
    },

    // Autosave now rather than on the debounce - for a step or section change,
    // where the user has visibly moved on and expects the previous part kept.
    flush: function (reason) { clearTimeout(timer); return save(reason || 'flush'); },

    isDirty: function () { return !!(reg && reg.isDirty()); },
    status: function () { return Object.assign({}, status); },
    onStatus: function (fn) {
      statusSubs.push(fn);
      try { fn(Object.assign({}, status), reg ? reg.isDirty() : false); } catch (e) {}
      return function () {
        var i = statusSubs.indexOf(fn);
        if (i >= 0) statusSubs.splice(i, 1);
      };
    },

    /* Recovery. Returns the stored draft for an id, or null. The caller decides
       whether to offer it - only it knows whether the draft is actually newer
       than the record, and offering to restore work that is already saved is its
       own kind of alarming. */
    peek: function (id) { return readDraft(id); },
    discard: function (id) { clearTimeout(timer); clearDraft(id); setStatus('idle'); },

    /* Called after an explicit Save succeeded: the record now holds this work, so
       the draft is no longer protecting anything and keeping it would make the
       next load offer to "recover" work that is already saved.

       clearTimeout FIRST. A save typically follows typing, so there is usually a
       debounced write already scheduled; without cancelling it, that write lands
       a second after the draft was cleared and resurrects it — and the next load
       offers to recover work that is already saved, which is the exact thing this
       method exists to prevent. */
    settled: function (id) { clearTimeout(timer); clearDraft(id); setStatus('idle'); },

    /* A persistent draft-state indicator — B5 / T4.4.

       The suite already showed "✓ All changes saved", but that badge belonged to
       the OUTBOX: it reported whether saved records had reached the project, and
       went green when the queue emptied whether or not anything in the form had
       been saved at all. This indicator speaks only for the draft, and the outbox
       badge's wording now names the project explicitly, so neither can be read as
       the other.

       role="status" so the state is announced politely (S10 / T4.5); a failure
       swaps in role="alert" so it interrupts, because a failed autosave means the
       safety net is not there and waiting for a pause to say so is too late. */
    mountIndicator: function (host, opts) {
      if (!host) return function () {};
      opts = opts || {};
      var el = document.createElement('div');
      el.className = 'wp-draft-status';
      el.id = opts.id || 'wp-draft-status';
      host.appendChild(el);

      function fmt(ts) {
        try { return new Date(ts).toLocaleTimeString(); } catch (e) { return ''; }
      }

      var un = window.WPAutosave.onStatus(function (st, dirty) {
        var role = 'status', cls = '', text = '';
        if (st.state === 'failed') {
          role = 'alert';
          cls = 'is-failed';
          text = '⚠ Draft not saved on this device — ' + (st.error || 'storage unavailable');
        } else if (st.state === 'saving') {
          cls = 'is-saving';
          text = '↻ Saving draft…';
        } else if (st.state === 'saved') {
          cls = 'is-saved';
          text = '✓ Draft saved at ' + fmt(st.at);
        } else {
          cls = 'is-idle';
          // "No unsaved changes" is a different statement from "saved", and it is
          // the true one when nothing has been typed.
          text = dirty ? 'Unsaved changes' : 'No unsaved changes';
        }
        el.className = 'wp-draft-status ' + cls;
        el.setAttribute('role', role);
        el.textContent = text;
        // Retry is only offered where it can do something.
        if (st.state === 'failed') {
          var b = document.createElement('button');
          b.type = 'button';
          b.className = 'wp-draft-retry';
          b.textContent = 'Retry';
          b.onclick = function () { window.WPAutosave.flush('retry'); };
          el.appendChild(b);
        }
      });
      return function () { un(); if (el.parentNode) el.parentNode.removeChild(el); };
    },

    _key: draftKey,
  };
})(window, document);