api: Add stream/update event

Fixes: zulip#182

lib/api/model/events.dart

@@ -40,7 +40,7 @@ sealed class Event {
         switch (json['op'] as String) {
           case 'create': return ChannelCreateEvent.fromJson(json);
           case 'delete': return ChannelDeleteEvent.fromJson(json);
-          // TODO(#182): case 'update': …
+          case 'update': return ChannelUpdateEvent.fromJson(json);
           default: return UnexpectedEvent.fromJson(json);
         }
       case 'subscription':
@@ -379,8 +379,73 @@ class ChannelDeleteEvent extends ChannelEvent {
   Map<String, dynamic> toJson() => _$ChannelDeleteEventToJson(this);
 }
 
-// TODO(#182) ChannelUpdateEvent, for a [ChannelEvent] with op `update`:
-//   https://zulip.com/api/get-events#stream-update
+/// A [ChannelEvent] with op `update`: https://zulip.com/api/get-events#stream-update
+@JsonSerializable(fieldRename: FieldRename.snake)
+class ChannelUpdateEvent extends ChannelEvent {
+  @override
+  String get op => 'update';
+
+  final int streamId;
+  final String name;
+
+  /// The name of the channel property, or null if we don't recognize it.
+  @JsonKey(unknownEnumValue: JsonKey.nullForUndefinedEnumValue)
+  final ChannelPropertyName? property;
+
+  /// The new value, or null if we don't recognize the property.
+  ///
+  /// This will have the type appropriate for [property]; for example,
+  /// if the property is boolean, then `value is bool` will always be true.
+  /// This invariant is enforced by [ChannelUpdateEvent.fromJson].
+  @JsonKey(readValue: _readValue)
+  final Object? value;
+
+  final String? renderedDescription;
+  final bool? historyPublicToSubscribers;
+  final bool? isWebPublic;
+
+  ChannelUpdateEvent({
+    required super.id,
+    required this.streamId,
+    required this.name,
+    required this.property,
+    required this.value,
+    this.renderedDescription,
+    this.historyPublicToSubscribers,
+    this.isWebPublic,
+  });
+
+  /// [value], with a check that its type corresponds to [property]
+  /// (e.g., `value as bool`).
+  static Object? _readValue(Map<dynamic, dynamic> json, String key) {
+    final value = json['value'];
+    switch (ChannelPropertyName.fromRawString(json['property'] as String)) {
+      case ChannelPropertyName.name:
+      case ChannelPropertyName.description:
+        return value as String;
+      case ChannelPropertyName.firstMessageId:
+        return value as int?;
+      case ChannelPropertyName.inviteOnly:
+        return value as bool;
+      case ChannelPropertyName.messageRetentionDays:
+        return value as int?;
+      case ChannelPropertyName.channelPostPolicy:
+        return ChannelPostPolicy.fromInt(value as int?);
+      case ChannelPropertyName.canRemoveSubscribersGroup:
+      case ChannelPropertyName.canRemoveSubscribersGroupId:
+      case ChannelPropertyName.streamWeeklyTraffic:
+        return value as int?;
+      case null:
+        return null;
+    }
+  }
+
+  factory ChannelUpdateEvent.fromJson(Map<String, dynamic> json) =>
+    _$ChannelUpdateEventFromJson(json);
+
+  @override
+  Map<String, dynamic> toJson() => _$ChannelUpdateEventToJson(this);
+}
 
 /// A Zulip event of type `subscription`.
 ///

lib/api/model/model.dart

@@ -391,6 +391,45 @@ enum ChannelPostPolicy {
     .map((key, value) => MapEntry(value, key));
 }
 
+/// The name of the [ZulipStream] properties that gets updated through [ChannelUpdateEvent.property].
+///
+/// In Zulip event-handling code (for [ChannelUpdateEvent]),
+/// we switch exhaustively on a value of this type
+/// to ensure that every property change in [ZulipStream] responds to the event.
+///
+/// Fields on [ZulipStream] not present here:
+///   streamId, dateCreated
+/// Each of those is immutable on any given channel, and there is no
+/// [ChannelUpdateEvent] that updates them.
+///
+/// Other fields on [ZulipStream] not present here:
+///   renderedDescription, historyPublicToSubscribers, isWebPublic
+/// Each of those are updated through separate fields of [ChannelUpdateEvent]
+/// with the same names.
+@JsonEnum(fieldRename: FieldRename.snake, alwaysCreate: true)
+enum ChannelPropertyName {
+  name,
+  description,
+  firstMessageId,
+  inviteOnly,
+  messageRetentionDays,
+  @JsonValue('stream_post_policy')
+  channelPostPolicy,
+  canRemoveSubscribersGroup,
+  canRemoveSubscribersGroupId, // TODO(Zulip-6): remove, replaced by canRemoveSubscribersGroup
+  streamWeeklyTraffic;
+
+  /// Get a [ChannelPropertyName] from a raw, snake-case string we recognize, else null.
+  ///
+  /// Example:
+  ///   'invite_only' -> ChannelPropertyName.inviteOnly
+  static ChannelPropertyName? fromRawString(String raw) => _byRawString[raw];
+
+  // _$…EnumMap is thanks to `alwaysCreate: true` and `fieldRename: FieldRename.snake`
+  static final _byRawString = _$ChannelPropertyNameEnumMap
+    .map((key, value) => MapEntry(value, key));
+}
+
 /// As in `subscriptions` in the initial snapshot.
 ///
 /// For docs, search for "subscriptions:"

lib/model/channel.dart

@@ -199,6 +199,51 @@ class ChannelStoreImpl with ChannelStore {
           streamsByName.remove(stream.name);
           subscriptions.remove(stream.streamId);
         }
+
+      case ChannelUpdateEvent():
+        final ChannelUpdateEvent(:streamId, name: String streamName) = event;
+        assert(identical(streams[streamId], streamsByName[streamName]));
+        assert(subscriptions[streamId] == null
+          || identical(subscriptions[streamId], streams[streamId]));
+
+        final channel = streams[streamId];
+        if (channel == null) return;
+
+        if (event.renderedDescription != null) {
+          channel.renderedDescription = event.renderedDescription!;
+        }
+        if (event.historyPublicToSubscribers != null) {
+          channel.historyPublicToSubscribers = event.historyPublicToSubscribers!;
+        }
+        if (event.isWebPublic != null) {
+          channel.isWebPublic = event.isWebPublic!;
+        }
+
+        if (event.property == null) {
+          // unrecognized property; do nothing
+          return;
+        }
+        switch (event.property!) {
+          case ChannelPropertyName.name:
+            channel.name = event.value as String;
+            streamsByName.remove(streamName);
+            streamsByName[channel.name] = channel;
+          case ChannelPropertyName.description:
+            channel.description = event.value as String;
+          case ChannelPropertyName.firstMessageId:
+            channel.firstMessageId = event.value as int?;
+          case ChannelPropertyName.inviteOnly:
+            channel.inviteOnly = event.value as bool;
+          case ChannelPropertyName.messageRetentionDays:
+            channel.messageRetentionDays = event.value as int?;
+          case ChannelPropertyName.channelPostPolicy:
+            channel.channelPostPolicy = event.value as ChannelPostPolicy;
+          case ChannelPropertyName.canRemoveSubscribersGroup:
+          case ChannelPropertyName.canRemoveSubscribersGroupId:
+            channel.canRemoveSubscribersGroup = event.value as int?;
+          case ChannelPropertyName.streamWeeklyTraffic:
+            channel.streamWeeklyTraffic = event.value as int?;
+        }
     }
   }
 

test/example_data.dart

@@ -650,6 +650,37 @@ ReactionEvent reactionEvent(Reaction reaction, ReactionOp op, int messageId) {
   );
 }
 
+ChannelUpdateEvent channelUpdateEvent(
+  ZulipStream stream, {
+  required ChannelPropertyName property,
+  required Object? value,
+}) {
+  switch (property) {
+    case ChannelPropertyName.name:
+    case ChannelPropertyName.description:
+      assert(value is String);
+    case ChannelPropertyName.firstMessageId:
+      assert(value is int?);
+    case ChannelPropertyName.inviteOnly:
+      assert(value is bool);
+    case ChannelPropertyName.messageRetentionDays:
+      assert(value is int?);
+    case ChannelPropertyName.channelPostPolicy:
+      assert(value is ChannelPostPolicy);
+    case ChannelPropertyName.canRemoveSubscribersGroup:
+    case ChannelPropertyName.canRemoveSubscribersGroupId:
+    case ChannelPropertyName.streamWeeklyTraffic:
+      assert(value is int?);
+  }
+  return ChannelUpdateEvent(
+    id: 1,
+    streamId: stream.streamId,
+    name: stream.name,
+    property: property,
+    value: value,
+  );
+}
+
 ////////////////////////////////////////////////////////////////
 // The entire per-account or global state.
 //

test/model/channel_test.dart

@@ -56,6 +56,17 @@ void main() {
 
       await store.addSubscription(eg.subscription(stream1));
       checkUnified(store);
+
+      await store.handleEvent(eg.channelUpdateEvent(store.streams[stream1.streamId]!,
+        property: ChannelPropertyName.name, value: 'new stream',
+      ));
+      checkUnified(store);
+
+      await store.handleEvent(eg.channelUpdateEvent(store.streams[stream1.streamId]!,
+        property: ChannelPropertyName.channelPostPolicy,
+        value: ChannelPostPolicy.administrators,
+      ));
+      checkUnified(store);
     });
   });