PERF: Ignore repeated PresenceChannel leave/join calls (#19638)

If a consumer is calling leave or join on a channel repeatedly, that should not trigger additional HTTP requests

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

@@ -66,15 +66,19 @@ class PresenceChannel extends EmberObject.extend(Evented) {
     }
 
     this.setProperties({ activeOptions });
+    if (!this.present) {
       await this.presenceService._enter(this);
       this.set("present", true);
     }
+  }
 
   // Mark the current user as leaving this channel
   async leave() {
+    if (this.present) {
       await this.presenceService._leave(this);
       this.set("present", false);
     }
+  }
 
   async subscribe(initialData = null) {
     if (this.subscribed) {

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

@@ -292,6 +292,39 @@ acceptance("Presence - Entering and Leaving", function (needs) {
     );
   });
 
+  test("join should be a no-op if already present", async function (assert) {
+    const presenceService = this.container.lookup("service:presence");
+    const channel = presenceService.getChannel("/test/ch1");
+
+    await channel.enter();
+    assert.strictEqual(requests.length, 1, "updated the server for enter");
+
+    await channel.enter();
+    assert.strictEqual(
+      requests.length,
+      1,
+      "does not update the server unnecessarily"
+    );
+  });
+
+  test("leave should be a no-op if not present", async function (assert) {
+    const presenceService = this.container.lookup("service:presence");
+    const channel = presenceService.getChannel("/test/ch1");
+
+    await channel.enter();
+    assert.strictEqual(requests.length, 1, "updated the server for enter");
+
+    await channel.leave();
+    assert.strictEqual(requests.length, 2, "updated the server for leave");
+
+    await channel.leave();
+    assert.strictEqual(
+      requests.length,
+      2,
+      "did not update the server unnecessarily"
+    );
+  });
+
   test("raises an error when entering a non-existent channel", async function (assert) {
     const presenceService = this.container.lookup("service:presence");
     const channel = presenceService.getChannel("/blah/does-not-exist");