autocomplete: Support @-wildcard in user-mention autocomplete

The implementation logic is similar to the zulip-mobile implementation:
  https://github.com/zulip/zulip-mobile/blob/a115df1f71c9dc31e9b41060a8d57b51c017d786/src/autocomplete/WildcardMentionItem.js

Fixes: #234

assets/l10n/app_ar.arb

@@ -1,3 +1,6 @@
 {
-
+  "notifyChannel": "إخطار القناة",
+  "notifyStream": "إخطار الدفق",
+  "notifyRecipients": "إخطار المستلمين",
+  "notifyTopic": "إخطار الموضوع"
 }

assets/l10n/app_en.arb

@@ -580,6 +580,22 @@
   "@manyPeopleTyping": {
     "description": "Text to display when there are multiple users typing."
   },
+  "notifyChannel": "Notify channel",
+  "@notifyChannel": {
+    "description": "Description for \"@all\", \"@everyone\", \"@channel\", and \"@stream\" wildcard mentions in a channel or topic narrow."
+  },
+  "notifyStream": "Notify stream",
+  "@notifyStream": {
+    "description": "Description for \"@all\", \"@everyone\", and \"@stream\" wildcard mentions in a stream or topic narrow."
+  },
+  "notifyRecipients": "Notify recipients",
+  "@notifyRecipients": {
+    "description": "Description for \"@all\" and \"@everyone\" wildcard mentions in a DM narrow."
+  },
+  "notifyTopic": "Notify topic",
+  "@notifyTopic": {
+    "description": "Description for \"@topic\" wildcard mention in a channel or topic narrow."
+  },
   "messageIsEditedLabel": "EDITED",
   "@messageIsEditedLabel": {
     "description": "Label for an edited message. (Use ALL CAPS for cased alphabets: Latin, Greek, Cyrillic, etc.)"

lib/generated/l10n/zulip_localizations.dart

@@ -859,6 +859,30 @@ abstract class ZulipLocalizations {
   /// **'Several people are typing…'**
   String get manyPeopleTyping;
 
+  /// Description for "@all", "@everyone", "@channel", and "@stream" wildcard mentions in a channel or topic narrow.
+  ///
+  /// In en, this message translates to:
+  /// **'Notify channel'**
+  String get notifyChannel;
+
+  /// Description for "@all", "@everyone", and "@stream" wildcard mentions in a stream or topic narrow.
+  ///
+  /// In en, this message translates to:
+  /// **'Notify stream'**
+  String get notifyStream;
+
+  /// Description for "@all" and "@everyone" wildcard mentions in a DM narrow.
+  ///
+  /// In en, this message translates to:
+  /// **'Notify recipients'**
+  String get notifyRecipients;
+
+  /// Description for "@topic" wildcard mention in a channel or topic narrow.
+  ///
+  /// In en, this message translates to:
+  /// **'Notify topic'**
+  String get notifyTopic;
+
   /// Label for an edited message. (Use ALL CAPS for cased alphabets: Latin, Greek, Cyrillic, etc.)
   ///
   /// In en, this message translates to:

lib/generated/l10n/zulip_localizations_ar.dart

@@ -461,6 +461,18 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get manyPeopleTyping => 'Several people are typing…';
 
+  @override
+  String get notifyChannel => 'إخطار القناة';
+
+  @override
+  String get notifyStream => 'إخطار الدفق';
+
+  @override
+  String get notifyRecipients => 'إخطار المستلمين';
+
+  @override
+  String get notifyTopic => 'إخطار الموضوع';
+
   @override
   String get messageIsEditedLabel => 'EDITED';
 

lib/generated/l10n/zulip_localizations_en.dart

@@ -461,6 +461,18 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get manyPeopleTyping => 'Several people are typing…';
 
+  @override
+  String get notifyChannel => 'Notify channel';
+
+  @override
+  String get notifyStream => 'Notify stream';
+
+  @override
+  String get notifyRecipients => 'Notify recipients';
+
+  @override
+  String get notifyTopic => 'Notify topic';
+
   @override
   String get messageIsEditedLabel => 'EDITED';
 

lib/generated/l10n/zulip_localizations_ja.dart

@@ -461,6 +461,18 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get manyPeopleTyping => 'Several people are typing…';
 
+  @override
+  String get notifyChannel => 'Notify channel';
+
+  @override
+  String get notifyStream => 'Notify stream';
+
+  @override
+  String get notifyRecipients => 'Notify recipients';
+
+  @override
+  String get notifyTopic => 'Notify topic';
+
   @override
   String get messageIsEditedLabel => 'EDITED';
 

lib/model/autocomplete.dart

@@ -423,8 +423,8 @@ class MentionAutocompleteView extends AutocompleteView<MentionAutocompleteQuery,
 
   factory MentionAutocompleteView.init({
     required PerAccountStore store,
-    required Narrow narrow,
     required MentionAutocompleteQuery query,
+    required Narrow narrow,
   }) {
     final view = MentionAutocompleteView._(
       store: store,
@@ -492,8 +492,6 @@ class MentionAutocompleteView extends AutocompleteView<MentionAutocompleteQuery,
     required String? topic,
     required PerAccountStore store,
   }) {
-    // TODO(#234): give preference to "all", "everyone" or "stream"
-
     // TODO(#618): give preference to subscribed users first
 
     if (streamId != null) {
@@ -598,9 +596,45 @@ class MentionAutocompleteView extends AutocompleteView<MentionAutocompleteQuery,
     return userAName.compareTo(userBName); // TODO(i18n): add locale-aware sorting
   }
 
+  List<WildcardMentionAutocompleteResult> get wildcardMentionResults {
+    final isChannelWildcardAvailable = store.account.zulipFeatureLevel >= 247; // TODO(server-9)
+    final isChannelOrTopicNarrow = narrow is ChannelNarrow || narrow is TopicNarrow;
+
+    final wildcardMentions = <WildcardMentionAutocompleteResult>[];
+    // Only one of the (all, everyone, channel, stream) channel wildcards are
+    // shown.
+    if (query.testWildcard(Wildcard.all)) {
+      wildcardMentions.add(WildcardMentionAutocompleteResult(
+        wildcard: Wildcard.all));
+    } else if (query.testWildcard(Wildcard.everyone)) {
+      wildcardMentions.add(WildcardMentionAutocompleteResult(
+        wildcard: Wildcard.everyone));
+    } else if (isChannelOrTopicNarrow) {
+      if (query.testWildcard(Wildcard.channel) && isChannelWildcardAvailable) {
+        wildcardMentions.add(WildcardMentionAutocompleteResult(
+          wildcard: Wildcard.channel));
+      } else if (query.testWildcard(Wildcard.stream)) {
+        wildcardMentions.add(WildcardMentionAutocompleteResult(
+          wildcard: Wildcard.stream));
+      }
+    }
+
+    final isTopicWildcardAvailable = store.account.zulipFeatureLevel >= 224; // TODO(sever-8)
+    if (isChannelOrTopicNarrow
+        && isTopicWildcardAvailable
+        && query.testWildcard(Wildcard.topic)) {
+      wildcardMentions.add(WildcardMentionAutocompleteResult(
+        wildcard: Wildcard.topic));
+    }
+    return wildcardMentions;
+  }
+
   @override
   Future<List<MentionAutocompleteResult>?> computeResults() async {
     final results = <MentionAutocompleteResult>[];
+    // Give priority to wildcard mentions.
+    results.addAll(wildcardMentionResults);
+
     if (await filterCandidates(filter: _testUser,
         candidates: sortedUsers, results: results)) {
       return null;
@@ -625,6 +659,9 @@ class MentionAutocompleteView extends AutocompleteView<MentionAutocompleteQuery,
   }
 }
 
+// The available user wildcard mention options.
+enum Wildcard { all, everyone, channel, stream, topic }
+
 /// A query the user has entered into some form of autocomplete.
 ///
 /// Subclasses correspond to different types of autocomplete interaction
@@ -694,9 +731,12 @@ class MentionAutocompleteQuery extends ComposeAutocompleteQuery {
     return MentionAutocompleteView.init(store: store, narrow: narrow, query: this);
   }
 
+  bool testWildcard(Wildcard wildcard) {
+    return wildcard.name.contains(raw.toLowerCase());
+  }
+
   bool testUser(User user, AutocompleteDataCache cache) {
     // TODO(#236) test email too, not just name
-
     if (!user.isActive) return false;
 
     return _testName(user, cache);
@@ -778,9 +818,13 @@ class UserMentionAutocompleteResult extends MentionAutocompleteResult {
   final int userId;
 }
 
-// TODO(#233): // class UserGroupMentionAutocompleteResult extends MentionAutocompleteResult {
+class WildcardMentionAutocompleteResult extends MentionAutocompleteResult {
+  WildcardMentionAutocompleteResult({required this.wildcard});
+
+  final Wildcard wildcard;
+}
 
-// TODO(#234): // class WildcardMentionAutocompleteResult extends MentionAutocompleteResult {
+// TODO(#233): // class UserGroupMentionAutocompleteResult extends MentionAutocompleteResult {
 
 /// An autocomplete interaction for choosing a topic for a message.
 class TopicAutocompleteView extends AutocompleteView<TopicAutocompleteQuery, TopicAutocompleteResult> {

lib/model/compose.dart

@@ -1,6 +1,7 @@
 import 'dart:math';
 
 import '../api/model/model.dart';
+import 'autocomplete.dart';
 import 'internal_link.dart';
 import 'narrow.dart';
 import 'store.dart';
@@ -101,18 +102,33 @@ String wrapWithBacktickFence({required String content, String? infoString}) {
   return resultBuffer.toString();
 }
 
-/// An @-mention, like @**Chris Bobbe|13313**.
+/// An @user-mention, like @**Chris Bobbe|13313**.
 ///
 /// To omit the user ID part ("|13313") whenever the name part is unambiguous,
 /// pass a Map of all users we know about. This means accepting a linear scan
 /// through all users; avoid it in performance-sensitive codepaths.
-String mention(User user, {bool silent = false, Map<int, User>? users}) {
+String userMention(User user, {bool silent = false, Map<int, User>? users}) {
   bool includeUserId = users == null
     || users.values.where((u) => u.fullName == user.fullName).take(2).length == 2;
 
   return '@${silent ? '_' : ''}**${user.fullName}${includeUserId ? '|${user.userId}' : ''}**';
 }
 
+/// An @wildcard-mention, like @**channel**.
+String wildcardMention(Wildcard wildcard, {
+  required PerAccountStore store,
+}) {
+  final isChannelWildcardAvailable = store.account.zulipFeatureLevel >= 247; // TODO(server-9)
+  assert(isChannelWildcardAvailable || wildcard != Wildcard.channel);
+  final isTopicWildcardAvailable = store.account.zulipFeatureLevel >= 224; // TODO(sever-8)
+  assert(isTopicWildcardAvailable || wildcard != Wildcard.topic);
+
+  final name = wildcard == Wildcard.stream && isChannelWildcardAvailable
+    ? Wildcard.channel.name
+    : wildcard.name;
+  return '@**$name**';
+}
+
 /// https://spec.commonmark.org/0.30/#inline-link
 ///
 /// The "link text" is made by enclosing [visibleText] in square brackets.
@@ -145,7 +161,7 @@ String quoteAndReplyPlaceholder(PerAccountStore store, {
     SendableNarrow.ofMessage(message, selfUserId: store.selfUserId),
     nearMessageId: message.id);
   // See note in [quoteAndReply] about asking `mention` to omit the |<id> part.
-  return '${mention(sender!, silent: true)} ${inlineLink('said', url)}: ' // TODO(i18n) ?
+  return '${userMention(sender!, silent: true)} ${inlineLink('said', url)}: ' // TODO(i18n) ?
     '*(loading message ${message.id})*\n'; // TODO(i18n) ?
 }
 
@@ -169,6 +185,6 @@ String quoteAndReply(PerAccountStore store, {
     // Could ask `mention` to omit the |<id> part unless the mention is ambiguous…
     // but that would mean a linear scan through all users, and the extra noise
     // won't much matter with the already probably-long message link in there too.
-    return '${mention(sender!, silent: true)} ${inlineLink('said', url)}:\n' // TODO(i18n) ?
+    return '${userMention(sender!, silent: true)} ${inlineLink('said', url)}:\n' // TODO(i18n) ?
       '${wrapWithBacktickFence(content: rawContent, infoString: 'quote')}';
 }

lib/widgets/autocomplete.dart

@@ -1,8 +1,11 @@
 import 'package:flutter/material.dart';
 
+import '../generated/l10n/zulip_localizations.dart';
 import '../model/emoji.dart';
+import '../model/store.dart';
 import 'content.dart';
 import 'emoji.dart';
+import 'icons.dart';
 import 'store.dart';
 import '../model/autocomplete.dart';
 import '../model/compose.dart';
@@ -197,7 +200,9 @@ class ComposeAutocomplete extends AutocompleteField<ComposeAutocompleteQuery, Co
         }
         // TODO(i18n) language-appropriate space character; check active keyboard?
         //   (maybe handle centrally in `controller`)
-        replacementString = '${mention(store.users[userId]!, silent: query.silent, users: store.users)} ';
+        replacementString = '${userMention(store.users[userId]!, silent: query.silent, users: store.users)} ';
+      case WildcardMentionAutocompleteResult(:var wildcard):
+        replacementString = '${wildcardMention(wildcard, store: store)} ';
     }
 
     controller.value = intent.textEditingValue.replaced(
@@ -211,7 +216,8 @@ class ComposeAutocomplete extends AutocompleteField<ComposeAutocompleteQuery, Co
   @override
   Widget buildItem(BuildContext context, int index, ComposeAutocompleteResult option) {
     final child = switch (option) {
-      MentionAutocompleteResult() => _MentionAutocompleteItem(option: option),
+      MentionAutocompleteResult() => _MentionAutocompleteItem(
+        option: option, narrow: narrow),
       EmojiAutocompleteResult() => _EmojiAutocompleteItem(option: option),
     };
     return InkWell(
@@ -223,28 +229,62 @@ class ComposeAutocomplete extends AutocompleteField<ComposeAutocompleteQuery, Co
 }
 
 class _MentionAutocompleteItem extends StatelessWidget {
-  const _MentionAutocompleteItem({required this.option});
+  const _MentionAutocompleteItem({required this.option, required this.narrow});
 
   final MentionAutocompleteResult option;
+  final Narrow narrow;
 
   @override
   Widget build(BuildContext context) {
+    final store = PerAccountStoreWidget.of(context);
     Widget avatar;
-    String label;
+    Widget label;
     switch (option) {
       case UserMentionAutocompleteResult(:var userId):
-        avatar = Avatar(userId: userId, size: 32, borderRadius: 3);
-        label = PerAccountStoreWidget.of(context).users[userId]!.fullName;
+        avatar = Avatar(userId: userId, size: 32, borderRadius: 3); // web uses 21px
+        label = Text(store.users[userId]!.fullName);
+      case WildcardMentionAutocompleteResult(:var wildcard):
+        avatar = const Icon(ZulipIcons.three_person, size: 29); // web uses 19px
+        label = wildcardLabel(wildcard, context: context, store: store);
     }
 
     return Padding(
       padding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 8.0),
       child: Row(children: [
         avatar,
         const SizedBox(width: 8),
-        Text(label),
+        label,
       ]));
   }
+
+  Widget wildcardLabel(Wildcard wildcard, {
+    required BuildContext context,
+    required PerAccountStore store,
+  }) {
+    final isDmNarrow = narrow is DmNarrow;
+    final isChannelWildcardAvailable = store.account.zulipFeatureLevel >= 247; // TODO(server-9)
+    final localizations = ZulipLocalizations.of(context);
+    final description = switch (wildcard) {
+      Wildcard.all => isDmNarrow
+        ? localizations.notifyRecipients
+        : isChannelWildcardAvailable
+            ? localizations.notifyChannel
+            : localizations.notifyStream,
+      Wildcard.everyone => isDmNarrow
+        ? localizations.notifyRecipients
+        : isChannelWildcardAvailable
+            ? localizations.notifyChannel
+            : localizations.notifyStream,
+      Wildcard.channel => localizations.notifyChannel,
+      Wildcard.stream => isChannelWildcardAvailable
+        ? localizations.notifyChannel
+        : localizations.notifyStream,
+      Wildcard.topic => localizations.notifyTopic,
+    };
+    return Text.rich(TextSpan(text: '${wildcard.name} ', children: [
+      TextSpan(text: description, style: TextStyle(fontSize: 12,
+        color: Colors.black.withValues(alpha: 0.8)))]));
+  }
 }
 
 class _EmojiAutocompleteItem extends StatelessWidget {