FIX: handle correctly the case when several subscribers call trackStatus() on the user model (#17497)

app/assets/javascripts/discourse/app/models/user.js

@@ -1180,23 +1180,37 @@ User.reopenClass(Singleton, {
 
 // user status tracking
 User.reopen(Evented, {
+  _subscribersCount: 0,
   _clearStatusTimerId: null,
 
   // always call stopTrackingStatus() when done with a user
   trackStatus() {
-    this.addObserver("status", this, "_statusChanged");
+    if (this._subscribersCount === 0) {
+      this.addObserver("status", this, "_statusChanged");
 
-    this.appEvents.on("user-status:changed", this, this._updateStatus);
+      this.appEvents.on("user-status:changed", this, this._updateStatus);
 
-    if (this.status && this.status.ends_at) {
-      this._scheduleStatusClearing(this.status.ends_at);
+      if (this.status && this.status.ends_at) {
+        this._scheduleStatusClearing(this.status.ends_at);
+      }
     }
+
+    this._subscribersCount++;
   },
 
   stopTrackingStatus() {
-    this.removeObserver("status", this, "_statusChanged");
-    this.appEvents.off("user-status:changed", this, this._updateStatus);
-    this._unscheduleStatusClearing();
+    if (this._subscribersCount === 0) {
+      return;
+    }
+
+    if (this._subscribersCount === 1) {
+      // the last subscriber is unsubscribing
+      this.removeObserver("status", this, "_statusChanged");
+      this.appEvents.off("user-status:changed", this, this._updateStatus);
+      this._unscheduleStatusClearing();
+    }
+
+    this._subscribersCount--;
   },
 
   _statusChanged(sender, key) {

app/assets/javascripts/discourse/tests/unit/models/user-test.js

@@ -5,13 +5,7 @@ import PreloadStore from "discourse/lib/preload-store";
 import sinon from "sinon";
 import { settled } from "@ember/test-helpers";
 
-module("Unit | Model | user", function (hooks) {
-  hooks.afterEach(function () {
-    if (this.clock) {
-      this.clock.restore();
-    }
-  });
-
+module("Unit | Model | user", function () {
   test("staff", function (assert) {
     let user = User.create({ id: 1, username: "eviltrout" });
 
@@ -112,6 +106,29 @@ module("Unit | Model | user", function (hooks) {
     assert.ok(spyMomentGuess.notCalled);
   });
 
+  test("subsequent calls to trackStatus and stopTrackingStatus increase and decrease subscribers counter", function (assert) {
+    const user = User.create();
+    assert.equal(user._subscribersCount, 0);
+
+    user.trackStatus();
+    assert.equal(user._subscribersCount, 1);
+
+    user.trackStatus();
+    assert.equal(user._subscribersCount, 2);
+
+    user.stopTrackingStatus();
+    assert.equal(user._subscribersCount, 1);
+
+    user.stopTrackingStatus();
+    assert.equal(user._subscribersCount, 0);
+  });
+
+  test("attempt to stop tracking status if status wasn't tracked doesn't throw", function (assert) {
+    const user = User.create();
+    user.stopTrackingStatus();
+    assert.ok(true);
+  });
+
   test("clears statuses of several users correctly when receiving status updates via appEvents", function (assert) {
     const status1 = {
       description: "user1 status",