Prefetch visible post threads after a bounded reading dwell

1 files changed, 27 insertions, 6 deletions

diff --git a/src/features/messages.js b/src/features/messages.js
index 53f6c99..759b155 100644
--- a/src/features/messages.js
+++ b/src/features/messages.js
@@ -32,6 +32,7 @@ import { saveInbox } from '../dm-inbox.js';
 import { loadMediaIndex, saveMediaIndex, wipeMediaIndex } from '../media-cache.js';
 import { mergeFeedWindow } from '../feed-window.js';
 import { createThreadStore } from '../thread-cache.js';
+import { createThreadPrefetch } from '../thread-prefetch.js';
 import { createFeedCache, FEED_CACHE_POSTS, FEED_SEED_POSTS } from '../feed-cache.js';
 import { POPULAR_RELAYS, FIREHOSE_RELAYS, popularCandidates } from '../popular-feed.js';
 import { makeSearcher, resultRows, fallbackAvatar, warmSearch, punkImageUrl, punkSmallUrl, primalCache } from '../recipient-search.js';
@@ -8841,10 +8842,12 @@ export function messagesFeature(ctx) {
     const flagged = !pending && !(ui.revealed && ui.revealed.has(ev.id)) ? reportsOn(ev) : null;
     if (flagged) return foldedRow(ev, flagged);
     const openable = open && !pending;
+    if (openable) threadPrefetch.watch(ev);
     if (!pending) watchZaps([ev.id]);
     return h('div', {
       class: 'row note-post',
       'data-zap-post': ev.id,
+      'data-thread-prefetch': openable ? ev.id : undefined,
       'data-focus-note': focus ? '1' : undefined,
       style: 'padding:10px 0'
         + (openable ? ';cursor:pointer' : '')
@@ -8888,6 +8891,18 @@ export function messagesFeature(ctx) {
   // ---- thread view: a note in its conversation ----------------------------
   const threadCache = new Map(); // root id -> { status, root, replies }
   const threadStore = createThreadStore();
+  const threadPrefetch = createThreadPrefetch({
+    key: rootIdOf,
+    cached: (ev) => threadCache.has(rootIdOf(ev)),
+    load: (ev) => threadFor(ev, true).loading,
+  });
+  function trimPrefetchedThreads() {
+    const idle = [...new Set(threadCache.values())].filter((c) => c.prefetched
+      && c.status === 'ready' && ui.noteThread?.rootId !== c.rootId);
+    for (const c of idle.slice(0, Math.max(0, idle.length - 12))) {
+      for (const [id, entry] of threadCache) if (entry === c) threadCache.delete(id);
+    }
+  }
   const persistThread = (c) => {
     if (!c.root) return;
     const faces = {};
@@ -8959,13 +8974,18 @@ export function messagesFeature(ctx) {
     const marked = es.find((x) => x[3] === 'root');
     return (marked || es[0] || [])[1] || ev.id;
   }
-  function threadFor(seed) {
+  function threadFor(seed, prefetch = false) {
     const requestedRootId = rootIdOf(seed);
     let c = threadCache.get(requestedRootId) || [...new Set(threadCache.values())]
       .find((c) => c.replies.some((e) => e.id === seed.id || e.id === requestedRootId));
     if (c) {
       threadCache.set(requestedRootId, c);
-      c.focusId = seed.id;
+      if (!prefetch) {
+        c.focusId = seed.id;
+        const wasPrefetched = c.prefetched;
+        c.prefetched = false;
+        if (wasPrefetched && c.status === 'ready') persistThread(c);
+      }
       if (seed.id === c.rootId) c.root ||= seed;
       else if (!c.replies.some((ev) => ev.id === seed.id)) {
         c.replies = [...c.replies, seed].sort((a, b) => a.created_at - b.created_at);
@@ -8992,14 +9012,14 @@ export function messagesFeature(ctx) {
     }
     for (const q of stored?.quotes || []) if (!quoted.get(q.id)?.ev) quoted.set(q.id, { status: 'ready', ev: q, at: Date.now() });
     const rootId = stored?.rootId || requestedRootId;
-    c = { status: stored ? 'ready' : 'loading', rootId, focusId: seed.id,
+    c = { status: stored ? 'ready' : 'loading', rootId, focusId: seed.id, prefetched: prefetch,
       root: stored?.root || (seed.id === rootId ? seed : null), replies: stored?.replies || [], counts: stored?.counts || {} };
     if (seed.id !== rootId && !c.replies.some((e) => e.id === seed.id)) c.replies.push(seed);
     c.replies.sort((a, b) => a.created_at - b.created_at);
     threadCache.set(requestedRootId, c);
     threadCache.set(rootId, c);
     if (ui.noteThread?.focusId === seed.id) ui.noteThread.rootId = rootId;
-    (async () => {
+    c.loading = (async () => {
       // Where a thread lives: the reply's author, the people it tags (the
       // root's author is usually first among them), the relay hints on its
       // e tags, and ours. The reply author's relays alone missed roots
@@ -9052,7 +9072,7 @@ export function messagesFeature(ctx) {
         .filter((e) => e && e.id !== c.rootId && !seen.has(e.id) && seen.add(e.id))
         .sort((a, b) => a.created_at - b.created_at);
       c.status = 'ready';
-      persistThread(c);
+      if (!c.prefetched) persistThread(c);
       if (ui.noteThread && ui.noteThread.rootId === c.rootId) {
         renderThreadStable();
         // The inline reply box may have MOVED on this render (it slots under
@@ -9068,7 +9088,7 @@ export function messagesFeature(ctx) {
     })().catch(() => {
       c.status = 'ready';
       if (ui.noteThread && ui.noteThread.rootId === c.rootId) renderThreadStable();
-    });
+    }).finally(trimPrefetchedThreads);
     return c;
   }
   function openNoteThread(ev) {
@@ -13250,6 +13270,7 @@ export function messagesFeature(ctx) {
       clearTimeout(feedAheadTimer); feedAheadTimer = null;
       for (const c of feedStates.values()) c.stopped = true;
       feedStates.clear();
+      threadPrefetch.stop();
       threadCache.clear();
       follows = null; followsAt = 0; feed = null; relayLists = null;
       mutes = null; mutesAt = 0;