support undoing a reaction

src/domain/session/room/timeline/ReactionsViewModel.js

@@ -86,7 +86,11 @@ class ReactionViewModel extends ViewModel {
         return this._annotation.count - other._annotation.count;
     }
 
-    react() {
+    toggleReaction() {
+        if (this.haveReacted) {
+            return this._parentEntry.redactReaction(this.key);
+        } else {
             return this._parentEntry.react(this.key);
         }
+    }
 }

src/domain/session/room/timeline/tiles/BaseMessageTile.js

@@ -123,7 +123,14 @@ export class BaseMessageTile extends SimpleTile {
     }
 
     react(key) {
-        this._room.sendEvent("m.reaction", this._entry.annotate(key));
+        return this._room.sendEvent("m.reaction", this._entry.annotate(key));
+    }
+
+    async redactReaction(key) {
+        const id = await this._entry.getOwnAnnotationId(this._room, key);
+        if (id) {
+            this._room.sendRedaction(id);
+        }
     }
 
     _updateReactions() {

src/matrix/room/BaseRoom.js

@@ -28,6 +28,7 @@ import {EventEntry} from "./timeline/entries/EventEntry.js";
 import {ObservedEventMap} from "./ObservedEventMap.js";
 import {DecryptionSource} from "../e2ee/common.js";
 import {ensureLogItem} from "../../logging/utils.js";
+import {ANNOTATION_RELATION_TYPE, getRelation} from "./timeline/relations.js";
 
 const EVENT_ENCRYPTED_TYPE = "m.room.encrypted";
 
@@ -451,6 +452,21 @@ export class BaseRoom extends EventEmitter {
         return observable;
     }
 
+    async getOwnAnnotationEventId(targetId, key) {
+        const txn = await this._storage.readWriteTxn([
+            this._storage.storeNames.timelineEvents,
+            this._storage.storeNames.timelineRelations,
+        ]);
+        const relations = await txn.timelineRelations.getForTargetAndType(this.id, targetId, ANNOTATION_RELATION_TYPE);
+        for (const relation of relations) {
+            const annotation = await txn.timelineEvents.getByEventId(this.id, relation.sourceEventId);
+            if (annotation.event.sender === this._user.id && getRelation(annotation.event).key === key) {
+                return annotation.event.event_id;
+            }
+        }
+        return null;
+    }
+
     async _readEventById(eventId) {
         let stores = [this._storage.storeNames.timelineEvents];
         if (this.isEncrypted) {

src/matrix/room/timeline/entries/EventEntry.js

@@ -130,4 +130,8 @@ export class EventEntry extends BaseEventEntry {
     get annotations() {
         return this._eventEntry.annotations;
     }
+
+    getOwnAnnotationId(room, key) {
+        return room.getOwnAnnotationEventId(this.id, key);
+    }
 }

src/matrix/room/timeline/entries/PendingEventEntry.js

@@ -85,4 +85,9 @@ export class PendingEventEntry extends BaseEventEntry {
     get relatedEventId() {
         return this._pendingEvent.relatedEventId;
     }
+
+    getOwnAnnotationId(_, key) {
+        // TODO: implement this once local reactions are implemented
+        return null;
+    }
 }

src/platform/web/ui/css/themes/element/timeline.css

@@ -217,6 +217,11 @@ only loads when the top comes into view*/
     grid-area: reactions;
 }
 
+.Timeline_messageReactions button.haveReacted {
+    background-color: green;
+    color: white;
+}
+
 .AnnouncementView {
     margin: 5px 0;
     padding: 5px 10%;

src/platform/web/ui/session/room/timeline/ReactionsView.js

@@ -32,12 +32,11 @@ class ReactionView extends TemplateView {
     render(t, vm) {
         const haveReacted = vm => vm.haveReacted;
         return t.button({
-            disabled: haveReacted,
             className: {haveReacted},
         }, [vm.key, " ", vm => `${vm.count}`]);
     }
 
     onClick() {
-        this.value.react();
+        this.value.toggleReaction();
     }
 }