autocomplete: Introduce a field for sorted users

This field will be used to maintain a list of sorted users based on the
most relevant autocomplete criteria in the upcoming commits.

Co-authored-by: Greg Price <[email protected]>

Author: sm-sayedi

lib/model/autocomplete.dart

@@ -178,6 +178,7 @@ class MentionAutocompleteView extends ChangeNotifier {
   @override
   void dispose() {
     store.autocompleteViewManager.unregisterMentionAutocomplete(this);
+    _sortedUsers = null;
     // We cancel in-progress computations by checking [hasListeners] between tasks.
     // After [super.dispose] is called, [hasListeners] returns false.
     // TODO test that logic (may involve detecting an unhandled Future rejection; how?)
@@ -201,6 +202,7 @@ class MentionAutocompleteView extends ChangeNotifier {
   /// This will redo the search from scratch for the current query, if any.
   void reassemble() {
     if (_query != null) {
+      _sortedUsers = null;
       _startSearch(_query!);
     }
   }
@@ -230,22 +232,43 @@ class MentionAutocompleteView extends ChangeNotifier {
     notifyListeners();
   }
 
+  List<User>? _sortedUsers;
+
+  List<User> sortByRelevance({required List<User> users}) {
+    return users; // TODO(#228) sort for most relevant first
+  }
+
+  void _sortUsers() {
+    final users = store.users.values.toList();
+    _sortedUsers = sortByRelevance(users: users);
+  }
+
   Future<List<MentionAutocompleteResult>?> _computeResults(MentionAutocompleteQuery query) async {
     final List<MentionAutocompleteResult> results = [];
-    final Iterable<User> users = store.users.values;
 
-    final iterator = users.iterator;
+    if (_sortedUsers == null) {
+      _sortUsers();
+    }
+
+    final sortedUsers = _sortedUsers!;
+    final iterator = sortedUsers.iterator;
     bool isDone = false;
     while (!isDone) {
       // CPU perf: End this task; enqueue a new one for resuming this work
       await Future(() {});
 
+      if (_sortedUsers != sortedUsers) {
+        // The list of users this loop has been working from has become stale.
+        // Abort so _startSearch can retry with the new list.
+        throw ConcurrentModificationError();
+      }
+
       if (query != _query || !hasListeners) { // false if [dispose] has been called.
         return null;
       }
 
       for (int i = 0; i < 1000; i++) {
-        if (!iterator.moveNext()) { // Can throw ConcurrentModificationError
+        if (!iterator.moveNext()) {
           isDone = true;
           break;
         }
@@ -256,7 +279,7 @@ class MentionAutocompleteView extends ChangeNotifier {
         }
       }
     }
-    return results; // TODO(#228) sort for most relevant first
+    return results;
   }
 }
 

lib/model/store.dart

@@ -447,16 +447,6 @@ class PerAccountStore extends ChangeNotifier with StreamStore {
           user.profileData = null;
         }
       }
-      // The following two lines will eventually not change [users], but are here to
-      // trigger a modification to the collection as only changing the properties
-      // of [user] does not signal a modification of [users] where needed.
-      //
-      // One example of this is [MentionAutocompleteView._computeResults] which
-      // throws a `ConcurrentModificationError` when there is a modification done
-      // to [users].
-      users[-1] = user;
-      users.remove(-1);
-
       autocompleteViewManager.handleRealmUserUpdateEvent(event);
       notifyListeners();
     } else if (event is StreamEvent) {