[D1X] Pull out follow-backs for higher signal (#4719)

* Pull out follow-backs for higher signal

* Gate it

* Fix early gate check

---------

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

3 files changed, 25 insertions, 6 deletions

diff --git a/src/state/queries/notifications/feed.ts b/src/state/queries/notifications/feed.ts
index 13ca3ffde..17ee90929 100644
--- a/src/state/queries/notifications/feed.ts
+++ b/src/state/queries/notifications/feed.ts
@@ -26,6 +26,7 @@ import {
   useQueryClient,
 } from '@tanstack/react-query'
 
+import {useGate} from '#/lib/statsig/statsig'
 import {useAgent} from '#/state/session'
 import {useModerationOpts} from '../../preferences/moderation-opts'
 import {STALE} from '..'
@@ -56,6 +57,7 @@ export function useNotificationFeedQuery(opts?: {enabled?: boolean}) {
   const unreads = useUnreadNotificationsApi()
   const enabled = opts?.enabled !== false
   const lastPageCountRef = useRef(0)
+  const gate = useGate()
 
   const query = useInfiniteQuery<
     FeedPage,
@@ -81,6 +83,7 @@ export function useNotificationFeedQuery(opts?: {enabled?: boolean}) {
             queryClient,
             moderationOpts,
             fetchAdditionalData: true,
+            shouldUngroupFollowBacks: () => gate('ungroup_follow_backs'),
           })
         ).page
       }
diff --git a/src/state/queries/notifications/unread.tsx b/src/state/queries/notifications/unread.tsx
index 7bb325ea9..b5f7d0d60 100644
--- a/src/state/queries/notifications/unread.tsx
+++ b/src/state/queries/notifications/unread.tsx
@@ -8,6 +8,7 @@ import {useQueryClient} from '@tanstack/react-query'
 import EventEmitter from 'eventemitter3'
 
 import BroadcastChannel from '#/lib/broadcast'
+import {useGate} from '#/lib/statsig/statsig'
 import {logger} from '#/logger'
 import {useAgent, useSession} from '#/state/session'
 import {resetBadgeCount} from 'lib/notifications/notifications'
@@ -47,6 +48,7 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
   const agent = useAgent()
   const queryClient = useQueryClient()
   const moderationOpts = useModerationOpts()
+  const gate = useGate()
 
   const [numUnread, setNumUnread] = React.useState('')
 
@@ -149,6 +151,7 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
             // only fetch subjects when the page is going to be used
             // in the notifications query, otherwise skip it
             fetchAdditionalData: !!invalidate,
+            shouldUngroupFollowBacks: () => gate('ungroup_follow_backs'),
           })
           const unreadCount = countUnread(page)
           const unreadCountStr =
@@ -189,7 +192,7 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
         }
       },
     }
-  }, [setNumUnread, queryClient, moderationOpts, agent])
+  }, [setNumUnread, queryClient, moderationOpts, agent, gate])
   checkUnreadRef.current = api.checkUnread
 
   return (
diff --git a/src/state/queries/notifications/util.ts b/src/state/queries/notifications/util.ts
index ade98b317..2f2c242d8 100644
--- a/src/state/queries/notifications/util.ts
+++ b/src/state/queries/notifications/util.ts
@@ -30,6 +30,7 @@ export async function fetchPage({
   queryClient,
   moderationOpts,
   fetchAdditionalData,
+  shouldUngroupFollowBacks,
 }: {
   agent: BskyAgent
   cursor: string | undefined
@@ -37,6 +38,7 @@ export async function fetchPage({
   queryClient: QueryClient
   moderationOpts: ModerationOpts | undefined
   fetchAdditionalData: boolean
+  shouldUngroupFollowBacks?: () => boolean
 }): Promise<{page: FeedPage; indexedAt: string | undefined}> {
   const res = await agent.listNotifications({
     limit,
@@ -51,7 +53,7 @@ export async function fetchPage({
   )
 
   // group notifications which are essentially similar (follows, likes on a post)
-  let notifsGrouped = groupNotifications(notifs)
+  let notifsGrouped = groupNotifications(notifs, {shouldUngroupFollowBacks})
 
   // we fetch subjects of notifications (usually posts) now instead of lazily
   // in the UI to avoid relayouts
@@ -109,6 +111,7 @@ export function shouldFilterNotif(
 
 export function groupNotifications(
   notifs: AppBskyNotificationListNotifications.Notification[],
+  options?: {shouldUngroupFollowBacks?: () => boolean},
 ): FeedNotification[] {
   const groupedNotifs: FeedNotification[] = []
   for (const notif of notifs) {
@@ -123,10 +126,20 @@ export function groupNotifications(
           notif.reasonSubject === groupedNotif.notification.reasonSubject &&
           notif.author.did !== groupedNotif.notification.author.did
         ) {
-          groupedNotif.additional = groupedNotif.additional || []
-          groupedNotif.additional.push(notif)
-          grouped = true
-          break
+          const nextIsFollowBack =
+            notif.reason === 'follow' && notif.author.viewer?.following
+          const prevIsFollowBack =
+            groupedNotif.notification.reason === 'follow' &&
+            groupedNotif.notification.author.viewer?.following
+          const shouldUngroup =
+            (nextIsFollowBack || prevIsFollowBack) &&
+            options?.shouldUngroupFollowBacks?.()
+          if (!shouldUngroup) {
+            groupedNotif.additional = groupedNotif.additional || []
+            groupedNotif.additional.push(notif)
+            grouped = true
+            break
+          }
         }
       }
     }