Sorts chats by the latest message in Discovery

app/src/main/java/com/vitorpamplona/amethyst/model/Channel.kt

@@ -108,10 +108,9 @@ class LiveActivitiesChannel(val address: ATag) : Channel(address.toTag()) {
 @Stable
 abstract class Channel(val idHex: String) {
     var creator: User? = null
-
     var updatedMetadataAt: Long = 0
-
     val notes = LargeCache<HexKey, Note>()
+    var lastNoteCreatedAt: Long = 0
 
     open fun id() = Hex.decode(idHex)
 
@@ -147,6 +146,10 @@ abstract class Channel(val idHex: String) {
 
     fun addNote(note: Note) {
         notes.put(note.idHex, note)
+
+        if ((note.createdAt() ?: 0) > lastNoteCreatedAt) {
+            lastNoteCreatedAt = note.createdAt() ?: 0
+        }
     }
 
     fun removeNote(note: Note) {

app/src/main/java/com/vitorpamplona/amethyst/ui/dal/DiscoverChatFeedFilter.kt

@@ -85,17 +85,15 @@ open class DiscoverChatFeedFilter(val account: Account) : AdditiveFeedFilter<Not
     }
 
     override fun sort(collection: Set<Note>): List<Note> {
-        val followingKeySet =
-            account.liveDiscoveryFollowLists.value?.users ?: account.liveKind3Follows.value.users
-
-        val counter = ParticipantListBuilder()
-        val participantCounts =
-            collection.associate { it to counter.countFollowsThatParticipateOn(it, followingKeySet) }
+        val lastNote =
+            collection.associateWith { note ->
+                LocalCache.getChannelIfExists(note.idHex)?.lastNoteCreatedAt ?: 0
+            }
 
         return collection
             .sortedWith(
                 compareBy(
-                    { participantCounts[it] },
+                    { lastNote[it] },
                     { it.createdAt() },
                     { it.idHex },
                 ),