Paginate notifications

src/lib/components/Notifications.svelte

@@ -7,12 +7,27 @@
   import {
     notificationsStore,
     markNotificationsSeen,
+    loadMoreNotifications,
     type Notification,
   } from "$lib/notifications.svelte";
   import { summarize } from "$lib/seo";
   import * as nip19 from "@nostr/tools/nip19";
 
+  const PAGE = 5;
+
   const items = $derived(notificationsStore.items);
+  // Visible slice; "Show more" reveals another page from what is loaded and
+  // fetches older ones once the loaded list runs out.
+  let shown = $state(PAGE);
+  const visible = $derived(items?.slice(0, shown) ?? null);
+  const hasMore = $derived(
+    !!items && (items.length > shown || !notificationsStore.done),
+  );
+
+  async function showMore() {
+    if (items && items.length <= shown) await loadMoreNotifications();
+    shown += PAGE;
+  }
 
   // Unread threshold frozen when the list first shows, so new items keep their
   // mark while on screen even though they are counted as seen right away.
@@ -20,7 +35,13 @@
 
   $effect(() => {
     if (!items) return;
-    if (openedAt === null) openedAt = untrack(() => notificationsStore.seenAt);
+    if (openedAt === null) {
+      const seenAt = untrack(() => notificationsStore.seenAt);
+      openedAt = seenAt;
+      // Every new item is visible at once; the page size is only a floor
+      const unread = items.filter((n) => n.createdAt > seenAt).length;
+      shown = Math.max(PAGE, unread);
+    }
     markNotificationsSeen();
   });
 
@@ -86,7 +107,7 @@
     </p>
   {:else}
     <ul class="divide-y divide-neutral-100 dark:divide-neutral-800">
-      {#each items as n (n.id)}
+      {#each visible ?? [] as n (n.id)}
         {@const unread = n.createdAt > (openedAt ?? 0)}
         {@const name = authorName(n.pubkey)}
         {@const picture = authorPicture(n.pubkey)}
@@ -163,5 +184,18 @@
         </li>
       {/each}
     </ul>
+    {#if hasMore}
+      {@const busy = notificationsStore.loadingMore}
+      <div class="flex justify-center py-6">
+        <button
+          onclick={showMore}
+          disabled={busy}
+          aria-busy={busy}
+          class="rounded border border-neutral-200 px-6 py-1.5 text-sm font-medium text-neutral-700 hover:bg-neutral-50 disabled:opacity-50 dark:border-neutral-700 dark:text-neutral-300 dark:hover:bg-neutral-800"
+        >
+          {busy ? "Loading…" : "Show more"}
+        </button>
+      </div>
+    {/if}
   {/if}
 </section>

src/lib/forum/notifications.ts

@@ -20,7 +20,13 @@ export type Notification = {
   title?: string; // thread title, filled by fetchThreadTitles
 };
 
-export const NOTIFICATIONS_LIMIT = 50;
+export const NOTIFICATIONS_PAGE = 20;
+const CURSOR_HEADROOM = 10; // boundary events re-read at the inclusive cursor
+
+export type NotificationPage = {
+  items: Notification[];
+  done: boolean; // no older notifications left
+};
 
 // Classify an event that p-tags the user. Own events and anything that is
 // neither a discussion reply nor a chat message yield null.
@@ -69,23 +75,32 @@ export async function fetchThreadTitles(
   }
 }
 
-// Latest replies and mentions addressed to the user, newest first. Without
-// `groupId` every group the relay serves the caller counts.
+// One page of replies and mentions addressed to the user, newest first,
+// older than the cursor. Without `groupId` every group the relay serves the
+// caller counts.
 export async function fetchNotifications(
   q: Query,
   me: string,
-  groupId?: string,
-): Promise<Notification[]> {
+  req: { groupId?: string; until?: number; exclude?: Set<string> } = {},
+): Promise<NotificationPage> {
+  const n = NOTIFICATIONS_PAGE;
+  const exclude = req.exclude ?? new Set<string>();
   const events = await q({
     kinds: [1111, 9],
     "#p": [me],
-    ...(groupId ? { "#h": [groupId] } : {}),
-    limit: NOTIFICATIONS_LIMIT,
+    ...(req.groupId ? { "#h": [req.groupId] } : {}),
+    ...(req.until ? { until: req.until } : {}),
+    limit: n + CURSOR_HEADROOM,
   });
-  const items = events
+  const fresh = events
+    .filter((e) => !exclude.has(e.id))
     .map((e) => parseNotification(e, me))
-    .filter((n): n is Notification => n !== null)
+    .filter((x): x is Notification => x !== null)
     .sort((a, b) => b.createdAt - a.createdAt);
+  const items = fresh.slice(0, n);
+  // Finished only when everything fresh fits the page and the relay had
+  // nothing beyond the requested window
+  const done = fresh.length <= n && events.length < n + CURSOR_HEADROOM;
   await fetchThreadTitles(q, items);
-  return items;
+  return { items, done };
 }

src/lib/notifications.svelte.ts

@@ -6,14 +6,18 @@ import {
   fetchThreadTitles,
   parseNotification,
   type Notification,
+  type NotificationPage,
 } from "$lib/forum/notifications";
 
 export type { Notification };
 
 const SEEN_KEY = "notifications_seen";
+const scope = () => (MODE === "simple" ? GROUP_ID : undefined);
 
 let pubkey = $state<string | null>(null);
 let items = $state<Notification[] | null>(null);
+let done = $state(true);
+let loadingMore = $state(false);
 let seenAt = $state(0);
 let liveSub: { close(): void } | null = null;
 let req = 0; // supersedes an in-flight load on login/logout
@@ -33,6 +37,12 @@ export const notificationsStore = {
   get items() {
     return items;
   },
+  get done() {
+    return done;
+  },
+  get loadingMore() {
+    return loadingMore;
+  },
   get seenAt() {
     return seenAt;
   },
@@ -55,23 +65,24 @@ export async function startNotifications(pk: string) {
   pubkey = pk;
   seenAt = readSeen(pk);
   const current = ++req;
-  const scope = MODE === "simple" ? GROUP_ID : undefined;
+  const groupId = scope();
 
-  let result: Notification[] = [];
+  let result: NotificationPage = { items: [], done: true };
   try {
-    result = await fetchNotifications(queryForum, pk, scope);
+    result = await fetchNotifications(queryForum, pk, { groupId });
   } catch (e) {
     console.error("[notifications] load failed", e);
   }
   if (current !== req) return;
-  items = result;
-  for (const n of result) ensureProfile(n.pubkey);
+  items = result.items;
+  done = result.done;
+  for (const n of result.items) ensureProfile(n.pubkey);
 
   liveSub = subscribeForum(
     {
       kinds: [1111, 9],
       "#p": [pk],
-      ...(scope ? { "#h": [scope] } : {}),
+      ...(groupId ? { "#h": [groupId] } : {}),
       since: Math.floor(Date.now() / 1000),
     },
     {
@@ -97,9 +108,35 @@ export function stopNotifications() {
   liveSub = null;
   pubkey = null;
   items = null;
+  done = true;
+  loadingMore = false;
   seenAt = 0;
 }
 
+// Append the next page of older notifications.
+export async function loadMoreNotifications() {
+  const pk = pubkey;
+  const current = req;
+  if (!pk || !items || done || loadingMore) return;
+  loadingMore = true;
+  const oldest = items[items.length - 1];
+  try {
+    const next = await fetchNotifications(queryForum, pk, {
+      groupId: scope(),
+      until: oldest?.createdAt,
+      exclude: new Set(items.map((n) => n.id)),
+    });
+    if (current !== req || !items) return;
+    items = [...items, ...next.items];
+    done = next.done;
+    for (const n of next.items) ensureProfile(n.pubkey);
+  } catch (e) {
+    console.error("[notifications] failed to load more", e);
+  } finally {
+    if (current === req) loadingMore = false;
+  }
+}
+
 // Everything loaded so far counts as read.
 export function markNotificationsSeen() {
   if (!pubkey) return;