autocomplete [nfc]: Factor out generic AutocompleteView

The mechanism of query and results is generic to the idea of
autocomplete in general, it's not specific to autocomplete on
@-mentions vs. topics vs. anything else.

Author: Khader-1

lib/model/autocomplete.dart

@@ -8,7 +8,7 @@ import 'narrow.dart';
 import 'store.dart';
 
 extension ComposeContentAutocomplete on ComposeContentController {
-  AutocompleteIntent? autocompleteIntent() {
+  AutocompleteIntent<MentionAutocompleteQuery>? autocompleteIntent() {
     if (!selection.isValid || !selection.isNormalized) {
       // We don't require [isCollapsed] to be true because we've seen that
       // autocorrect and even backspace involve programmatically expanding the
@@ -68,8 +68,8 @@ final RegExp mentionAutocompleteMarkerRegex = (() {
     unicode: true);
 })();
 
-/// The content controller's recognition that the user might want autocomplete UI.
-class AutocompleteIntent {
+/// The text controller's recognition that the user might want autocomplete UI.
+class AutocompleteIntent<QueryT extends AutocompleteQuery> {
   AutocompleteIntent({
     required this.syntaxStart,
     required this.query,
@@ -91,7 +91,7 @@ class AutocompleteIntent {
   // that use a custom/subclassed [TextEditingValue], so that's not convenient.
   final int syntaxStart;
 
-  final MentionAutocompleteQuery query; // TODO other autocomplete query types
+  final QueryT query;
 
   /// The [TextEditingValue] whose text [syntaxStart] refers to.
   final TextEditingValue textEditingValue;
@@ -151,21 +151,90 @@ class AutocompleteViewManager {
   // void dispose() { … }
 }
 
-/// A view-model for a mention-autocomplete interaction.
+/// A view-model for an autocomplete interaction.
 ///
 /// The owner of one of these objects must call [dispose] when the object
 /// will no longer be used, in order to free resources on the [PerAccountStore].
 ///
 /// Lifecycle:
-///  * Create with [init].
+///  * Create an instance of a concrete subtype.
 ///  * Add listeners with [addListener].
 ///  * Use the [query] setter to start a search for a query.
 ///  * On reassemble, call [reassemble].
 ///  * When the object will no longer be used, call [dispose] to free
 ///    resources on the [PerAccountStore].
-class MentionAutocompleteView extends ChangeNotifier {
+abstract class AutocompleteView<QueryT extends AutocompleteQuery, ResultT extends AutocompleteResult, CandidateT> extends ChangeNotifier {
+  AutocompleteView({required this.store});
+
+  final PerAccountStore store;
+
+  Iterable<CandidateT> getSortedItemsToTest(QueryT query);
+
+  ResultT? testItem(QueryT query, CandidateT item);
+
+  QueryT? get query => _query;
+  QueryT? _query;
+  set query(QueryT? query) {
+    _query = query;
+    if (query != null) {
+      _startSearch(query);
+    }
+  }
+
+  /// Called when the app is reassembled during debugging, e.g. for hot reload.
+  ///
+  /// This will redo the search from scratch for the current query, if any.
+  void reassemble() {
+    if (_query != null) {
+      _startSearch(_query!);
+    }
+  }
+
+  Iterable<ResultT> get results => _results;
+  List<ResultT> _results = [];
+
+  Future<void> _startSearch(QueryT query) async {
+    final newResults = await _computeResults(query);
+    if (newResults == null) {
+      // Query was old; new search is in progress. Or, no listeners to notify.
+      return;
+    }
+
+    _results = newResults;
+    notifyListeners();
+  }
+
+  Future<List<ResultT>?> _computeResults(QueryT query) async {
+    final List<ResultT> results = [];
+    final Iterable<CandidateT> data = getSortedItemsToTest(query);
+
+    final iterator = data.iterator;
+    bool isDone = false;
+    while (!isDone) {
+      // CPU perf: End this task; enqueue a new one for resuming this work
+      await Future(() {});
+
+      if (query != _query || !hasListeners) { // false if [dispose] has been called.
+        return null;
+      }
+
+      for (int i = 0; i < 1000; i++) {
+        if (!iterator.moveNext()) {
+          isDone = true;
+          break;
+        }
+        final CandidateT item = iterator.current;
+        final result = testItem(query, item);
+        if (result != null) results.add(result);
+      }
+    }
+    return results;
+  }
+}
+
+class MentionAutocompleteView extends AutocompleteView<MentionAutocompleteQuery, MentionAutocompleteResult, User> {
   MentionAutocompleteView._({
-    required this.store,
+    required super.store,
     required this.narrow,
     required this.sortedUsers,
   });
@@ -183,6 +252,9 @@ class MentionAutocompleteView extends ChangeNotifier {
     return view;
   }
 
+  final Narrow narrow;
+  final List<User> sortedUsers;
+
   static List<User> _usersByRelevance({
     required PerAccountStore store,
     required Narrow narrow,
@@ -279,6 +351,19 @@ class MentionAutocompleteView extends ChangeNotifier {
         streamId: streamId, senderId: userB.userId));
   }
 
+  @override
+  Iterable<User> getSortedItemsToTest(MentionAutocompleteQuery query) {
+    return sortedUsers;
+  }
+
+  @override
+  MentionAutocompleteResult? testItem(MentionAutocompleteQuery query, User item) {
+    if (query.testUser(item, store.autocompleteViewManager.autocompleteDataCache)) {
+      return UserMentionAutocompleteResult(userId: item.userId);
+    }
+    return null;
+  }
+
   /// Determines which of the two users is more recent in DM conversations.
   ///
   /// Returns a negative number if [userA] is more recent than [userB],
@@ -318,82 +403,44 @@ class MentionAutocompleteView extends ChangeNotifier {
     // TODO test that logic (may involve detecting an unhandled Future rejection; how?)
     super.dispose();
   }
+}
 
-  final PerAccountStore store;
-  final Narrow narrow;
-  final List<User> sortedUsers;
+abstract class AutocompleteQuery {
+  AutocompleteQuery(this.raw)
+    : _lowercaseWords = raw.toLowerCase().split(' ');
 
-  MentionAutocompleteQuery? get query => _query;
-  MentionAutocompleteQuery? _query;
-  set query(MentionAutocompleteQuery? query) {
-    _query = query;
-    if (query != null) {
-      _startSearch(query);
-    }
-  }
+  final String raw;
+  final List<String> _lowercaseWords;
 
-  /// Called when the app is reassembled during debugging, e.g. for hot reload.
+  /// Whether all of this query's words have matches in [words] that appear in order.
   ///
-  /// This will redo the search from scratch for the current query, if any.
-  void reassemble() {
-    if (_query != null) {
-      _startSearch(_query!);
-    }
-  }
-
-  Iterable<MentionAutocompleteResult> get results => _results;
-  List<MentionAutocompleteResult> _results = [];
-
-  Future<void> _startSearch(MentionAutocompleteQuery query) async {
-    final newResults = await _computeResults(query);
-    if (newResults == null) {
-      // Query was old; new search is in progress. Or, no listeners to notify.
-      return;
-    }
-
-    _results = newResults;
-    notifyListeners();
-  }
-
-  Future<List<MentionAutocompleteResult>?> _computeResults(MentionAutocompleteQuery query) async {
-    final List<MentionAutocompleteResult> results = [];
-    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 (query != _query || !hasListeners) { // false if [dispose] has been called.
-        return null;
+  /// A "match" means the word in [words] starts with the query word.
+  bool _testContainsQueryWords(List<String> words) {
+    // TODO(#237) test with diacritics stripped, where appropriate
+    int wordsIndex = 0;
+    int queryWordsIndex = 0;
+    while (true) {
+      if (queryWordsIndex == _lowercaseWords.length) {
+        return true;
+      }
+      if (wordsIndex == words.length) {
+        return false;
       }
 
-      for (int i = 0; i < 1000; i++) {
-        if (!iterator.moveNext()) {
-          isDone = true;
-          break;
-        }
-
-        final User user = iterator.current;
-        if (query.testUser(user, store.autocompleteViewManager.autocompleteDataCache)) {
-          results.add(UserMentionAutocompleteResult(userId: user.userId));
-        }
+      if (words[wordsIndex].startsWith(_lowercaseWords[queryWordsIndex])) {
+        queryWordsIndex++;
       }
+      wordsIndex++;
     }
-    return results;
   }
 }
 
-class MentionAutocompleteQuery {
-  MentionAutocompleteQuery(this.raw, {this.silent = false})
-    : _lowercaseWords = raw.toLowerCase().split(' ');
-
-  final String raw;
+class MentionAutocompleteQuery extends AutocompleteQuery {
+  MentionAutocompleteQuery(super.raw, {this.silent = false});
 
   /// Whether the user wants a silent mention (@_query, vs. @query).
   final bool silent;
 
-  final List<String> _lowercaseWords;
-
   bool testUser(User user, AutocompleteDataCache cache) {
     // TODO(#236) test email too, not just name
 
@@ -403,25 +450,7 @@ class MentionAutocompleteQuery {
   }
 
   bool _testName(User user, AutocompleteDataCache cache) {
-    // TODO(#237) test with diacritics stripped, where appropriate
-
-    final List<String> nameWords = cache.nameWordsForUser(user);
-
-    int nameWordsIndex = 0;
-    int queryWordsIndex = 0;
-    while (true) {
-      if (queryWordsIndex == _lowercaseWords.length) {
-        return true;
-      }
-      if (nameWordsIndex == nameWords.length) {
-        return false;
-      }
-
-      if (nameWords[nameWordsIndex].startsWith(_lowercaseWords[queryWordsIndex])) {
-        queryWordsIndex++;
-      }
-      nameWordsIndex++;
-    }
+    return _testContainsQueryWords(cache.nameWordsForUser(user));
   }
 
   @override
@@ -450,7 +479,9 @@ class AutocompleteDataCache {
   }
 }
 
-sealed class MentionAutocompleteResult {}
+class AutocompleteResult {}
+
+sealed class MentionAutocompleteResult extends AutocompleteResult {}
 
 class UserMentionAutocompleteResult extends MentionAutocompleteResult {
   UserMentionAutocompleteResult({required this.userId});

test/model/autocomplete_checks.dart

@@ -3,12 +3,12 @@ import 'package:zulip/model/autocomplete.dart';
 import 'package:zulip/widgets/compose_box.dart';
 
 extension ComposeContentControllerChecks on Subject<ComposeContentController> {
-  Subject<AutocompleteIntent?> get autocompleteIntent => has((c) => c.autocompleteIntent(), 'autocompleteIntent');
+  Subject<AutocompleteIntent<MentionAutocompleteQuery>?> get autocompleteIntent => has((c) => c.autocompleteIntent(), 'autocompleteIntent');
 }
 
-extension AutocompleteIntentChecks on Subject<AutocompleteIntent> {
+extension AutocompleteIntentChecks on Subject<AutocompleteIntent<AutocompleteQuery>> {
   Subject<int> get syntaxStart => has((i) => i.syntaxStart, 'syntaxStart');
-  Subject<MentionAutocompleteQuery> get query => has((i) => i.query, 'query');
+  Subject<AutocompleteQuery> get query => has((i) => i.query, 'query');
 }
 
 extension UserMentionAutocompleteResultChecks on Subject<UserMentionAutocompleteResult> {

test/widgets/compose_box_checks.dart

@@ -8,7 +8,7 @@ extension ComposeContentControllerChecks on Subject<ComposeContentController> {
 
 extension AutocompleteIntentChecks on Subject<AutocompleteIntent> {
   Subject<int> get syntaxStart => has((i) => i.syntaxStart, 'syntaxStart');
-  Subject<MentionAutocompleteQuery> get query => has((i) => i.query, 'query');
+  Subject<AutocompleteQuery> get query => has((i) => i.query, 'query');
 }
 
 extension UserMentionAutocompleteResultChecks on Subject<UserMentionAutocompleteResult> {