api: Implement TopicName.isSameAs(other) and .unresolve()

Author: chrisbobbe

lib/api/model/model.dart

@@ -669,6 +669,14 @@ extension type const TopicName(String _value) {
   //   https://github.com/zulip/zulip/blob/1fac99733/web/shared/src/resolved_topic.ts
   static const resolvedTopicPrefix = '✔ ';
 
+  /// Pattern for an arbitrary resolved-topic prefix.
+  ///
+  /// These always begin with [resolvedTopicPrefix]
+  /// but can be weird and go on longer, like "✔ ✔✔ ".
+  // This is RESOLVED_TOPIC_PREFIX_RE in web:
+  //   https://github.com/zulip/zulip/blob/1fac99733/web/shared/src/resolved_topic.ts#L4-L12
+  static final resolvedTopicPrefixRegexp = RegExp(r'^✔ [ ✔]*');
+
   /// The string this topic is identified by in the Zulip API.
   ///
   /// This should be used in constructing HTTP requests to the server,
@@ -687,6 +695,14 @@ extension type const TopicName(String _value) {
   /// The key to use for "same topic as" comparisons.
   String canonicalize() => apiName.toLowerCase();
 
+  /// A [TopicName] with [resolvedTopicPrefixRegexp] stripped if present.
+  TopicName unresolve() =>
+    TopicName(_value.replaceFirst(resolvedTopicPrefixRegexp, ''));
+
+  /// Whether [this] and [other] have the same canonical form,
+  /// using [canonicalize].
+  bool isSameAs(TopicName other) => canonicalize() == other.canonicalize();
+
   TopicName.fromJson(this._value);
 
   String toJson() => apiName;

test/api/model/model_test.dart

@@ -126,6 +126,43 @@ void main() {
     // MessageEditState group.
   });
 
+  group('TopicName', () {
+    test('unresolve', () {
+      void doCheck(TopicName input, TopicName expected) {
+        final output = input.unresolve();
+        check(output).apiName.equals(expected.apiName);
+      }
+
+      doCheck(eg.t('some topic'),       eg.t('some topic'));
+      doCheck(eg.t('Some Topic'),       eg.t('Some Topic'));
+      doCheck(eg.t('✔ some topic'),     eg.t('some topic'));
+      doCheck(eg.t('✔ Some Topic'),     eg.t('Some Topic'));
+
+      doCheck(eg.t('Some ✔ Topic'),     eg.t('Some ✔ Topic'));
+      doCheck(eg.t('✔ Some ✔ Topic'),   eg.t('Some ✔ Topic'));
+
+      doCheck(eg.t('✔ ✔✔✔ some topic'), eg.t('some topic'));
+      doCheck(eg.t('✔ ✔ ✔✔some topic'), eg.t('some topic'));
+    });
+
+    test('isSameAs', () {
+      void doCheck(TopicName topicA, TopicName topicB, bool expected) {
+        check(topicA.isSameAs(topicB)).equals(expected);
+      }
+
+      doCheck(eg.t('some topic'),   eg.t('some topic'),   true);
+      doCheck(eg.t('SOME TOPIC'),   eg.t('SOME TOPIC'),   true);
+      doCheck(eg.t('Some Topic'),   eg.t('sOME tOPIC'),   true);
+      doCheck(eg.t('✔ a'),          eg.t('✔ a'),          true);
+
+      doCheck(eg.t('✔ some topic'), eg.t('some topic'),   false);
+      doCheck(eg.t('SOME TOPIC'),   eg.t('✔ SOME TOPIC'), false);
+      doCheck(eg.t('✔ Some Topic'), eg.t('sOME tOPIC'),   false);
+
+      doCheck(eg.t('✔ a'),          eg.t('✔ b'),          false);
+    });
+  });
+
   group('DmMessage', () {
     final Map<String, dynamic> baseJson = Map.unmodifiable(deepToJson(
       eg.dmMessage(from: eg.otherUser, to: [eg.selfUser]),