Merge pull request #7536 from hayaksi1/fix/3434-mention-suggestion-ranking

Rank the mention suggestions by how well they match what was typed

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/messagecomposer/suggestions/SuggestionsProcessor.kt

@@ -115,9 +115,10 @@ class SuggestionsProcessor(
                 .filterUpTo(MAX_BATCH_ITEMS) { member ->
                     isJoinedMemberAndNotSelf(member) && memberMatchesQuery(member, query)
                 }
+                .sortedBy { member -> matchRank(member, query) }
                 .map(ResolvedSuggestion::Member)
 
-            if ("room".contains(query) && canSendRoomMention) {
+            if ("room".startsWith(query, ignoreCase = true) && canSendRoomMention) {
                 listOf(ResolvedSuggestion.AtRoom) + matchingMembers
             } else {
                 matchingMembers
@@ -125,6 +126,18 @@ class SuggestionsProcessor(
         }
     }
 
+    /**
+     * Members whose display name starts with the query come first, then members whose user id
+     * localpart starts with it, then the remaining matches on any other part of the name or id.
+     */
+    private fun matchRank(member: RoomMember, query: String): Int {
+        return when {
+            member.displayName?.startsWith(query, ignoreCase = true) == true -> 0
+            member.userId.extractedDisplayName.startsWith(query, ignoreCase = true) -> 1
+            else -> 2
+        }
+    }
+
     companion object {
         // We don't want to retrieve thousands of members
         private const val MAX_BATCH_ITEMS = 100

features/messages/impl/src/test/kotlin/io/element/android/features/messages/impl/messagecomposer/suggestions/SuggestionsProcessorTest.kt

@@ -383,6 +383,48 @@ class SuggestionsProcessorTest {
         )
     }
 
+    @Test
+    fun `processing Mention suggestion returns the members matching the start of the query first`() = runTest {
+        val matchingOnAnyPart = aRoomMember(userId = UserId("@carol:server.org"), displayName = "Not Alice")
+        val matchingOnUserIdStart = aRoomMember(userId = UserId("@alicia:server.org"), displayName = null)
+        val matchingOnDisplayNameStart = aRoomMember(userId = UserId("@zoe:server.org"), displayName = "Alice")
+        val result = suggestionsProcessor.process(
+            suggestion = aMentionSuggestion("ali"),
+            roomMembersState = RoomMembersState.Ready(
+                persistentListOf(matchingOnAnyPart, matchingOnUserIdStart, matchingOnDisplayNameStart)
+            ),
+            roomAliasSuggestions = emptyList(),
+            currentUserId = A_USER_ID_2,
+            canSendRoomMention = { false },
+            isInThread = false,
+        )
+        assertThat(result).isEqualTo(
+            listOf(
+                ResolvedSuggestion.Member(matchingOnDisplayNameStart),
+                ResolvedSuggestion.Member(matchingOnUserIdStart),
+                ResolvedSuggestion.Member(matchingOnAnyPart),
+            )
+        )
+    }
+
+    @Test
+    fun `processing Mention suggestion returns room ignoring the case of the query`() = runTest {
+        val aRoomMember = aRoomMember(userId = UserId("@alice:server.org"), displayName = "alice")
+        val result = suggestionsProcessor.process(
+            suggestion = aMentionSuggestion("RO"),
+            roomMembersState = RoomMembersState.Ready(persistentListOf(aRoomMember)),
+            roomAliasSuggestions = emptyList(),
+            currentUserId = A_USER_ID_2,
+            canSendRoomMention = { true },
+            isInThread = false,
+        )
+        assertThat(result).isEqualTo(
+            listOf(
+                ResolvedSuggestion.AtRoom,
+            )
+        )
+    }
+
     @Test
     fun `processing Mention suggestion with return matching display name but not room if not allowed`() = runTest {
         val aRoomMember = aRoomMember(userId = UserId("@alice:server.org"), displayName = "ro")