feat: prefetch the next mobile update (Closes #757)

frontend/dashboard.js

@@ -912,6 +912,7 @@
   });
   const notificationReader = createNotificationReader({
     load: fetchNotificationDetail,
+    getScope: () => confirmedOwnerLogin,
     loadConversation: fetchNotificationConversation,
     markRead: markNotificationRead,
     acknowledge: acknowledgeNotification,
@@ -978,6 +979,9 @@
     },
     onStatus: message => {
       qs('#update-sheet-status').textContent = message;
+      if (message === 'Update ready.' && updateTriage.active() && !offlineWorkMode) {
+        notificationReader.prefetch(updateTriage.next());
+      }
       qs('#retry-update-load').hidden = !message.startsWith('Could not load update.');
       if (message === 'Inbox cleared.') {
         qs('#my-work-action-status').textContent = message;
@@ -1001,6 +1005,7 @@
       progress.textContent = 'Update ' + state.index + ' of ' + state.total;
     },
     onFinish: () => {
+      notificationReader.prefetch();
       qs('#update-triage-progress').hidden = true;
       showMobileQueueCompletion('Updates');
     },

frontend/my-work.js

@@ -380,12 +380,27 @@ function createNotificationReader({
   loadConversation = null,
   onConversation = () => {},
   createPager = typeof createConversationPager === 'function' ? createConversationPager : null,
+  getScope = () => '',
 }) {
   let selected = null;
   let loadVersion = 0;
   let marking = false;
   let conversationPager = null;
   let offlineHydrated = false;
+  let prefetched = null;
+  let prefetchKey = '';
+
+  function prefetch(item) {
+    if (!item) { prefetched = null; prefetchKey = ''; return false; }
+    const notificationId = item?.notification_id;
+    if (!Number.isInteger(notificationId) || offlineHydrated) return false;
+    const key = getScope() + notificationId;
+    if (prefetchKey === key) return prefetched;
+    if (prefetched) return false;
+    prefetchKey = key;
+    prefetched = load(notificationId);
+    return prefetched;
+  }
 
   async function advanceAfterRead(items, current, queueing = false) {
     const updated = acknowledgeNotification(items, current.notification_id);
@@ -407,10 +422,19 @@ function createNotificationReader({
     selected = item;
     offlineHydrated = Boolean(savedDetail && !Array.isArray(savedDetail));
     const version = ++loadVersion;
+    const preload = !offlineHydrated && prefetchKey === getScope() + item.notification_id ? prefetched : null;
+    prefetched = null;
+    prefetchKey = '';
     onOpen(item);
-    onStatus('Loading update…');
+    if (!preload) onStatus('Loading update…');
     try {
-      const detail = offlineHydrated ? savedDetail : await load(item.notification_id);
+      let detail;
+      if (offlineHydrated) detail = savedDetail;
+      else if (preload) detail = await preload.catch(() => {
+        onStatus('Loading update…');
+        return load(item.notification_id);
+      });
+      else detail = await load(item.notification_id);
       if (selected !== item || version !== loadVersion) return false;
       onDetail(detail);
       if (createPager && loadConversation && detail.conversation) {
@@ -433,6 +457,7 @@ function createNotificationReader({
 
   return {
     open,
+    prefetch,
     commentPager() {
       return conversationPager;
     },
@@ -516,7 +541,7 @@ function createNotificationReplier({
         if ((storage.getItem(keyFor(item)) || '') !== body) storage.removeItem(operationKeyFor(item));
         storage.setItem(keyFor(item), body);
       }
-      catch (_error) { /* Keep the editable textarea as the fallback. */ }
+      catch (_error) {}
     },
     async submit(item, body, attachment = null) {
       if (pending) return false;
@@ -542,15 +567,15 @@ function createNotificationReplier({
             return { queued:true };
           }
           try { storage.removeItem(keyFor(item)); storage.removeItem(operationKeyFor(item)); }
-          catch (_error) { /* Confirmed delivery is authoritative. */ }
+          catch (_error) {}
           onStatus('Reply posted. You can mark this update read when ready.');
           return delivery.confirmed[0];
         }
         const result = await post(item.notification_id, body, operationId);
         try { storage.removeItem(keyFor(item)); }
-        catch (_error) { /* The posted reply is still authoritative. */ }
+        catch (_error) {}
         try { storage.removeItem(operationKeyFor(item)); }
-        catch (_error) { /* A confirmed result no longer needs replay identity. */ }
+        catch (_error) {}
         onStatus('Reply posted. You can mark this update read when ready.');
         return result;
       } catch (error) {

frontend/update-triage-session.js

@@ -35,6 +35,12 @@
       .map(id => byIdentity.get(id));
   }
 
+  function nextAvailable() {
+    if (!running || !state) return null;
+    const candidates = available().filter(item => identity(item) !== state.current);
+    return candidates.find(item => state.identities.indexOf(identity(item)) > state.identities.indexOf(state.current)) || candidates[0] || null;
+  }
+
   function finish() {
     running = false;
     state = null;
@@ -94,6 +100,7 @@
     completeAndNext: advance,
     acceptCompleted: () => advance(false),
     keepUnreadAndNext: advance,
+    next: nextAvailable,
     items: () => state ? available().slice() : [],
     end: finish,
   };