Share eager media pager loading across feed, profile, and grid

1 files changed, 47 insertions, 27 deletions

diff --git a/src/features/messages.js b/src/features/messages.js
index c273d32..59dc966 100644
--- a/src/features/messages.js
+++ b/src/features/messages.js
@@ -11512,7 +11512,7 @@ export function messagesFeature(ctx) {
   // time, no waiting on avatars, pictures and link cards (the grid shows
   // none of that), and the feed's own page of posts left as it was.
   let mediaCrawling = null;
-  function crawlMedia(c = feedNow()) {
+  function crawlMedia(c = feedNow(), kind = mediaMode === 'videos' ? 'videos' : 'images') {
     const def = feedDef(c.id);
     if (!def || !feedHasQuery(def)) return Promise.resolve();
     if (def.curated) return loadOlderFeed(); // a curated feed pages its own way
@@ -11522,7 +11522,6 @@ export function messagesFeature(ctx) {
       scheduleRepaint();
       // Clips are rare (one post in a hundred, on a busy relay), so a crawl
       // keeps reading pages until it has found a few, or read several.
-      const kind = mediaMode === 'videos' ? 'videos' : 'images';
       const had = r[kind].size;
       for (let pass = 0; pass < 5 && r[kind].size - had < 6; pass++) {
         const from = [r.until, c.notes.at(-1)?.created_at].filter(Boolean);
@@ -12824,9 +12823,7 @@ export function messagesFeature(ctx) {
       else if (pager.profile) markSeen(slide._ev);
       playSlide(slide);
       pagerCounts(slide);
-      // near the end: ask the feed for more, the pager picks them up
-      if (pagerSource()) pagerFeedAhead();
-      else { const gs = pagerGroups(); if (gs.indexOf(slide.closest('.mp-group')) >= gs.length - 3) crawlMedia().catch(() => {}); }
+      pagerLoadAhead();
     };
     pager.io = new IntersectionObserver((entries) => {
       for (const e of entries) {
@@ -12844,6 +12841,7 @@ export function messagesFeature(ctx) {
     if (first) pagerShow(first);
     pager.anchor = first; // the slide meant to be on screen, from the first moment
     pager.screenH = scroller.clientHeight;
+    pagerLoadAhead();
     // the clip on screen's seek bar, every frame (timeupdate comes a few times a second)
     if (video) {
       const p = pager;
@@ -12866,33 +12864,55 @@ export function messagesFeature(ctx) {
     };
     window.addEventListener('resize', pager.onResize);
     // new posts land in the feed while the pager is open; counts move
-    pager.tick = setInterval(() => { if (pager) { growPager(); pagerFeedAhead(); if (el.classList.contains('show')) pagerCounts(pager.cur); } }, 1500);
+    pager.tick = setInterval(() => { if (pager) { growPager(); pagerLoadAhead(); if (el.classList.contains('show')) pagerCounts(pager.cur); } }, 1500);
   }
-  // A pager opened from the feed walks the feed's own posts, which page in
-  // ten at a time as the feed is scrolled. Swiping is the scrolling here:
-  // with only a few posts left below the one on screen (PAGER_AHEAD), the feed pages on
-  // (the posts it holds, then older ones from the relays) until there are
-  // more — several pages if those posts carry none. A page that brings
-  // nothing (the feed busy, or at its end) stops it; the tick tries again.
-  // how many posts ahead to keep: clips are fewer and further between
-  // (more pages to find the next) and each is watched a while, so further
-  const PAGER_AHEAD = { images: 4, videos: 6 };
-  let pagerFeeding = false;
-  async function pagerFeedAhead() {
-    const src = pagerSource();
-    if (pagerFeeding || !src) return;
-    pagerFeeding = true;
+  // All media pagers build the same buffer, retaining the source's ordering
+  // and filters. The furthest post reached never moves back when we wrap,
+  // so pending refills continue while the reader circles through older items.
+  const PAGER_INITIAL = 30, PAGER_AHEAD = 20;
+  function pagerLoadSource(p) {
+    const src = pagerSource(p);
+    if (src) return {
+      more: src.more, done: src.done,
+      progress: () => src.c.shown + ':' + src.c.notes.length,
+    };
+    // A profile cache can be replaced while refreshing; never fall back
+    // to another source in that gap. The next timer tick will try again.
+    if (p.profile || p.fromFeed) return { more: async () => {}, done: () => true, progress: () => '' };
+    const c = feedNow(), r = mediaIndex(c.id);
+    const curated = feedDef(c.id)?.curated;
+    return {
+      more: () => crawlMedia(c, p.kind),
+      done: () => c.stopped || (curated ? c.end && c.shown >= c.notes.length : !!r.end),
+      progress: () => [r.until, r[p.kind].size, c.shown, c.notes.length].join(':'),
+    };
+  }
+  async function pagerLoadAhead() {
+    const p = pager;
+    if (!p) return;
+    const groups = pagerGroups();
+    const slide = p.cur || p.anchor;
+    p.furthest = Math.max(p.furthest ?? -1, groups.indexOf(slide && slide.closest('.mp-group')));
+    if (p.loadingAhead || Date.now() < (p.retryAheadAt || 0)) return;
+    p.loadingAhead = true;
+    let stalled = false;
     try {
-      const c = src.c;
-      for (let pages = 0; pages < 8 && pager && pagerSource(); pages++) {
-        const gs = pagerGroups();
-        if (gs.length - 1 - gs.indexOf(pager.cur && pager.cur.closest('.mp-group')) > (PAGER_AHEAD[pager.kind] || 4)) break;
-        const shown = c.shown, held = c.notes.length;
+      // Bound each run; the timer resumes if sparse media needs more pages.
+      for (let pages = 0; pages < 8 && pager === p; pages++) {
+        if (pagerGroups().length >= Math.max(PAGER_INITIAL, p.furthest + 1 + PAGER_AHEAD)) break;
+        const src = pagerLoadSource(p);
+        if (src.done()) break;
+        const before = src.progress();
         await src.more();
+        if (pager !== p) return;
         growPager();
-        if (c.shown === shown && c.notes.length === held) break;
+        if (src.progress() === before) { stalled = true; break; }
       }
-    } catch {} finally { pagerFeeding = false; }
+    } catch { stalled = true; } finally {
+      p.loadingAhead = false;
+      // An empty or busy source gets a breather, never concurrent requests.
+      p.retryAheadAt = Date.now() + (stalled ? 10000 : 1500);
+    }
   }
   // Slides for feed items the pager doesn't have yet: into their post's row
   // (a quote fetched late joins its post), a new post appended below (never