FIX: ensure presence channels 'leave' correctly when the tab is backgrounded

Co-authored-by: David Taylor <david@taylorhq.com>

app/assets/javascripts/discourse/app/services/presence.js

@@ -266,6 +266,7 @@ export default class PresenceService extends Service {
     this._presentProxies = new Map();
     this._subscribedProxies = new Map();
     this._initialDataRequests = new Map();
+    this._previousPresentButInactiveChannels = new Set();
 
     if (this.currentUser) {
       window.addEventListener("beforeunload", this._beaconLeaveAll);
@@ -512,6 +513,7 @@ export default class PresenceService extends Service {
 
     try {
       const presentChannels = [];
+      const presentButInactiveChannels = new Set();
       const channelsToLeave = queue
         .filter((e) => e.type === "leave")
         .map((e) => e.channel);
@@ -524,11 +526,19 @@ export default class PresenceService extends Service {
         ) {
           presentChannels.push(channelName);
         } else {
-          channelsToLeave.push(channelName);
+          presentButInactiveChannels.add(channelName);
+          if (!this._previousPresentButInactiveChannels.has(channelName)) {
+            channelsToLeave.push(channelName);
+          }
         }
       }
+      this._previousPresentButInactiveChannels = presentButInactiveChannels;
 
-      if (queue.length === 0 && presentChannels.length === 0) {
+      if (
+        queue.length === 0 &&
+        presentChannels.length === 0 &&
+        channelsToLeave.length === 0
+      ) {
         return;
       }
 

app/assets/javascripts/discourse/tests/unit/services/presence-test.js

@@ -426,6 +426,43 @@ module("Unit | Service | presence | entering and leaving", function (hooks) {
     );
   });
 
+  test("updates the server presence after going idle", async function (assert) {
+    const presenceService = getOwner(this).lookup("service:presence");
+    presenceService.currentUser = currentUser();
+    const channel = presenceService.getChannel("/test/ch1");
+
+    await channel.enter();
+    requests.pop(); // Throw away this request
+
+    setTestPresence(false);
+
+    await presenceService._updateServer();
+    assert.strictEqual(
+      requests.length,
+      1,
+      "updated the server after going idle"
+    );
+    let request = requests.pop();
+    assert.true(
+      request.getAll("leave_channels[]").includes("/test/ch1"),
+      "left ch1"
+    );
+
+    // Go back online
+    setTestPresence(true);
+    await presenceService._updateServer();
+    assert.strictEqual(
+      requests.length,
+      1,
+      "updated the server after going back online"
+    );
+    request = requests.pop();
+    assert.true(
+      request.getAll("present_channels[]").includes("/test/ch1"),
+      "rejoined ch1"
+    );
+  });
+
   test("handles the onlyWhileActive flag", async function (assert) {
     const presenceService = getOwner(this).lookup("service:presence");
     presenceService.currentUser = currentUser();