model: Add makeTopicKeyedMap for case-insensitive-but-preserving topic maps

Author: chrisbobbe

lib/model/channel.dart

@@ -1,3 +1,5 @@
+import 'dart:collection';
+
 import 'package:flutter/foundation.dart';
 
 import '../api/model/events.dart';
@@ -369,3 +371,21 @@ class ChannelStoreImpl with ChannelStore {
     }
   }
 }
+
+/// A [Map] with [TopicName] keys and [V] values.
+///
+/// When one of these is created by [makeTopicKeyedMap],
+/// key equality is done case-insensitively; see there.
+///
+/// This type should only be used for maps created by [makeTopicKeyedMap].
+/// It would be nice to enforce that.
+typedef TopicKeyedMap<V> = Map<TopicName, V>;
+
+/// Make a case-insensitive, case-preserving [TopicName]-keyed [LinkedHashMap].
+///
+/// The equality function is [TopicName.isSameAs],
+/// and the hash code is [String.hashCode] of [TopicName.canonicalize].
+TopicKeyedMap<V> makeTopicKeyedMap<V>() => LinkedHashMap<TopicName, V>(
+  equals: (a, b) => a.isSameAs(b),
+  hashCode: (k) => k.canonicalize().hashCode,
+);

test/model/channel_test.dart

@@ -7,7 +7,9 @@ import 'package:zulip/api/model/model.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/model/channel.dart';
 
+import '../api/model/model_checks.dart';
 import '../example_data.dart' as eg;
+import '../stdlib_checks.dart';
 import 'test_store.dart';
 
 void main() {
@@ -411,4 +413,30 @@ void main() {
         .equals(UserTopicVisibilityPolicy.none);
     });
   });
+
+  group('makeTopicKeyedMap', () {
+    test('"a" equals "A"', () {
+      final map = makeTopicKeyedMap<int>()
+        ..[eg.t('a')] = 1
+        ..[eg.t('A')] = 2;
+      check(map)
+        ..[eg.t('a')].equals(2)
+        ..[eg.t('A')].equals(2)
+        ..entries.which((it) => it.single
+          ..key.apiName.equals('a')
+          ..value.equals(2));
+    });
+
+    test('"A" equals "a"', () {
+      final map = makeTopicKeyedMap<int>()
+        ..[eg.t('A')] = 1
+        ..[eg.t('a')] = 2;
+      check(map)
+        ..[eg.t('A')].equals(2)
+        ..[eg.t('a')].equals(2)
+        ..entries.which((it) => it.single
+          ..key.apiName.equals('A')
+          ..value.equals(2));
+    });
+  });
 }

test/stdlib_checks.dart

@@ -16,6 +16,11 @@ extension ListChecks<T> on Subject<List<T>> {
   Subject<T> operator [](int index) => has((l) => l[index], '[$index]');
 }
 
+extension MapEntryChecks<K, V> on Subject<MapEntry<K, V>> {
+  Subject<K> get key => has((e) => e.key, 'key');
+  Subject<V> get value => has((e) => e.value, 'value');
+}
+
 extension NullableMapChecks<K, V> on Subject<Map<K, V>?> {
   void deepEquals(Map<Object?, Object?>? expected) {
     if (expected == null) {