fix: forget remembered entities after a while

TODO.md

@@ -3,6 +3,6 @@
 - ✔ React UI
 - ❌ Multiple rooms
 - ❌ Send relevant entity URIs to client; cache and use instead of full transfer
-- ❌ Forget remembered entities after a while
+- ✔ Forget remembered entities after a while
 - ❌ Optimize informed and Packer::pack: don't use .map on immutables
 - ❌ Optimize Damaging::tick

server/traits/informed.trait.js

@@ -1,3 +1,5 @@
+import {performance} from 'perf_hooks';
+
 import * as I from 'immutable';
 import immutablediff from 'immutablediff';
 
@@ -103,7 +105,9 @@ export class Informed extends decorate(Trait) {
         if (!(uuid in this._rememberedEntities)) {
           continue;
         }
-        const rememberedEntity = this._rememberedEntities[uuid];
+        const rememberedEntity = this._rememberedEntities[uuid].entity;
+        // Reset remembrance timeout.
+        this._rememberedEntities[uuid].rememberFor = 60;
         // Take a diff from what the client remembers to now.
         const currentState = state.getIn(
           ['room', 'layers', layerId, 'entityList', uuid]
@@ -163,7 +167,11 @@ export class Informed extends decorate(Trait) {
         if (!remembered) {
           return;
         }
-        this._rememberedEntities[uuid] = remembered;
+        this._rememberedEntities[uuid] = {
+          entity: remembered,
+          // Remember entities for one minute.
+          rememeberFor: 60,
+        };
         // Add overrides.
         const overrides = this.entityOverrides(
           removal.get('path'),
@@ -255,4 +263,14 @@ export class Informed extends decorate(Trait) {
     };
   }
 
+  tick(elapsed) {
+    const rememberedEntities = this._rememberedEntities;
+    for (const uuid in rememberedEntities) {
+      const rememberFor = rememberedEntities[uuid].rememberFor -= elapsed;
+      if (rememberFor <= 0) {
+        delete rememberedEntities[uuid];
+      }
+    }
+  }
+
 }