feat: allow reactions to particles in stream

Closes #111

js/src/lib/firestore-particles.ts

@@ -12,6 +12,8 @@ import {
   serverTimestamp,
   where,
   Timestamp,
+  arrayUnion,
+  arrayRemove,
   type DocumentData,
   type FirestoreDataConverter,
   type QueryDocumentSnapshot,
@@ -21,7 +23,7 @@ import {
 } from "firebase/firestore";
 import { firestoreDb } from "@/firebase";
 import { isContainerType, ParticleSchema } from "@/api/types";
-import type { Particle, ParticleType, ParticlePropertiesMap } from "@/api/types";
+import type { Particle, ParticleType, ParticlePropertiesMap, Reactions } from "@/api/types";
 
 // --- Converter ---
 
@@ -87,6 +89,7 @@ const particleConverter: FirestoreDataConverter<Particle> = {
           created_at: (raw.created_at as Timestamp).toDate(),
           created_by_human_id: raw.created_by_human_id,
           updated_at: raw.updated_at ? (raw.updated_at as Timestamp).toDate() : undefined,
+          reactions: raw.reactions ?? undefined,
         });
       default:
         throw new Error(`Unknown particle type: ${type}`);
@@ -342,3 +345,18 @@ export async function updateStreamPlaybackMarker(
     updated_at: serverTimestamp(),
   });
 }
+
+export async function toggleParticleReaction(
+  docPath: string,
+  emoji: string,
+  humanId: string,
+  currentReactions?: Reactions,
+): Promise<void> {
+  const particleRef = typedDoc(docPath);
+  const field = `reactions.${emoji}`;
+  const alreadyReacted = currentReactions?.[emoji]?.includes(humanId) ?? false;
+  await updateDoc(particleRef, {
+    [field]: alreadyReacted ? arrayRemove(humanId) : arrayUnion(humanId),
+    updated_at: serverTimestamp(),
+  });
+}