Include follow-based suggestions in interstitial (#4889)

src/components/FeedInterstitials.tsx

···
   const {currentAccount} = useSession()
   const userActionSnapshot = userActionHistory.useActionHistorySnapshot()
   const dids = React.useMemo(() => {
-    const {likes, follows, seen} = userActionSnapshot
+    const {likes, follows, followSuggestions, seen} = userActionSnapshot
     const likeDids = likes
       .map(l => new AtUri(l))
       .map(uri => uri.host)
       .filter(did => !follows.includes(did))
+    let suggestedDids: string[] = []
+    if (followSuggestions.length > 0) {
+      suggestedDids = [
+        // It's ok if these will pick the same item (weighed by its frequency)
+        followSuggestions[Math.floor(Math.random() * followSuggestions.length)],
+        followSuggestions[Math.floor(Math.random() * followSuggestions.length)],
+        followSuggestions[Math.floor(Math.random() * followSuggestions.length)],
+        followSuggestions[Math.floor(Math.random() * followSuggestions.length)],
+      ]
+    }
     const seenDids = seen
       .sort(sortSeenPosts)
       .map(l => new AtUri(l.uri))
       .map(uri => uri.host)
-    return [...new Set([...likeDids, ...seenDids])].filter(
+    return [...new Set([...suggestedDids, ...likeDids, ...seenDids])].filter(
       did => did !== currentAccount?.did,
     )
   }, [userActionSnapshot, currentAccount])

src/state/queries/profile.ts

···
   logContext: LogEvents['profile:follow']['logContext'] &
     LogEvents['profile:unfollow']['logContext'],
 ) {
+  const agent = useAgent()
   const queryClient = useQueryClient()
   const did = profile.did
   const initialFollowingUri = profile.viewer?.following
···
       updateProfileShadow(queryClient, did, {
         followingUri: finalFollowingUri,
       })
+
+      if (finalFollowingUri) {
+        agent.app.bsky.graph
+          .getSuggestedFollowsByActor({
+            actor: did,
+          })
+          .then(res => {
+            const dids = res.data.suggestions
+              .filter(a => !a.viewer?.following)
+              .map(a => a.did)
+              .slice(0, 8)
+            userActionHistory.followSuggestion(dids)
+          })
+      }
     },
   })
 

src/state/userActionHistory.ts

···
 
 const LIKE_WINDOW = 100
 const FOLLOW_WINDOW = 100
+const FOLLOW_SUGGESTION_WINDOW = 100
 const SEEN_WINDOW = 100
 
 export type SeenPost = {
···
    * The last 100 DIDs the user has followed
    */
   follows: string[]
+  /*
+   * The last 100 DIDs of suggested follows based on last follows
+   */
+  followSuggestions: string[]
   /**
    * The last 100 post URIs the user has seen from the Discover feed only
    */
···
 const userActionHistory: UserActionHistory = {
   likes: [],
   follows: [],
+  followSuggestions: [],
   seen: [],
 }
 
···
     .concat(dids)
     .slice(-FOLLOW_WINDOW)
 }
+
+export function followSuggestion(dids: string[]) {
+  userActionHistory.followSuggestions = userActionHistory.followSuggestions
+    .concat(dids)
+    .slice(-FOLLOW_SUGGESTION_WINDOW)
+}
+
 export function unfollow(dids: string[]) {
   userActionHistory.follows = userActionHistory.follows.filter(
     uri => !dids.includes(uri),