allow sending emoji/stickers from emote packs

lib/models/content/content.dart

@@ -16,6 +16,7 @@ import "package:nexus/models/content/server_acl.dart";
 import "package:nexus/models/content/topic.dart";
 import "package:nexus/models/content/sticker.dart";
 import "package:nexus/models/content/history_visibility.dart";
+import "package:nexus/models/content/image_pack.dart";
 
 class const Content({final String? parseError, final StackTrace? stackTrace}) {
   factory Content.fromJson(Map<String, dynamic> json) => const Content();
@@ -61,5 +62,7 @@ enum EventType(
   tombstone("m.room.tombstone", Content.fromJson),
   reaction("m.reaction", ReactionContent.fromJson),
   pinnedEvents("m.room.pinned_events", PinnedEventsContent.fromJson),
+  imagePack("m.room.image_pack", ImagePackContent.fromJson),
+  legacyImagePack("im.ponies.room_emotes", ImagePackContent.fromJson),
   message("m.room.message", MessageContent.fromJson),
 }

lib/models/content/image_pack.dart

@@ -0,0 +1,68 @@
+import "package:fast_immutable_collections/fast_immutable_collections.dart";
+import "package:freezed_annotation/freezed_annotation.dart";
+import "package:nexus/models/content/content.dart";
+import "package:nexus/models/info/image.dart";
+part "image_pack.freezed.dart";
+part "image_pack.g.dart";
+
+/// An image pack (MSC2545), from a room's state.
+@freezed
+sealed class ImagePackContent extends Content with _$ImagePackContent {
+  ImagePackContent._();
+  factory ImagePackContent({
+    @Default(IMap.empty()) IMap<String, PackImage> images,
+    PackInfo? pack,
+  }) = _ImagePackContent;
+
+  IMap<String, PackImage> imagesFor(ImageUsage usage) => images.where(
+    (_, image) => switch ((image.usage, pack?.usage ?? const .empty())) {
+      (final usages, _) when usages.isNotEmpty => usages.contains(usage),
+      (_, final packUsages) when packUsages.isNotEmpty => packUsages.contains(
+        usage,
+      ),
+      _ => true,
+    },
+  );
+
+  factory ImagePackContent.fromJson(Map<String, Object?> json) =>
+      _$ImagePackContentFromJson(json);
+}
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const PackImage({
+  required final Uri url,
+  final String? body,
+  final ImageInfo? info,
+  @JsonKey(fromJson: ImageUsage.setFromJson)
+  final ISet<ImageUsage> usage = const .empty(),
+}) with _$PackImage {
+  Map<String, Object?> toJson() => _$PackImageToJson(this);
+
+  factory PackImage.fromJson(Map<String, Object?> json) =>
+      _$PackImageFromJson(json);
+}
+
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const PackInfo({
+  final String? displayName,
+  final Uri? avatarUrl,
+  final String? attribution,
+  @JsonKey(fromJson: ImageUsage.setFromJson)
+  final ISet<ImageUsage> usage = const .empty(),
+}) with _$PackInfo {
+  Map<String, Object?> toJson() => _$PackInfoToJson(this);
+
+  factory PackInfo.fromJson(Map<String, Object?> json) =>
+      _$PackInfoFromJson(json);
+}
+
+enum ImageUsage {
+  emoticon,
+  sticker;
+
+  /// Ignores usages we don't know about.
+  static ISet<ImageUsage> setFromJson(List<dynamic>? json) =>
+      ISet(values.where((value) => json?.contains(value.name) ?? false));
+}

lib/models/content/reaction.dart

@@ -11,11 +11,15 @@ sealed class ReactionContent extends Content with _$ReactionContent {
 
   factory ReactionContent({
     @JsonKey(readValue: ReactionContent.keyJsonFromJson) String? key,
+
+    /// For custom emoji reactions
+    @JsonKey(name: "com.beeper.reaction.shortcode") String? shortcode,
   }) = _ReactionContent;
 
   @override
   Map<String, dynamic> toJson() => {
     "m.relates_to": {"key": key},
+    "com.beeper.reaction.shortcode": ?shortcode,
   };
 
   factory ReactionContent.fromJson(Map<String, Object?> json) =>