Group calling: Peek into a group call

ts/util/LatestQueue.ts

@@ -0,0 +1,69 @@
+// Copyright 2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+/**
+ * This class tries to enforce a state machine that looks something like this:
+ *
+ * .--------------------.  called   .-----------.  called  .---------------------.
+ * |                    | --------> |           | -------> |                     |
+ * | Nothing is running |           | 1 running |          | 1 running, 1 queued |
+ * |                    | <-------- |           | <------- |                     |
+ * '--------------------'   done    '-----------'   done   '---------------------'
+ *                                                             |           ^
+ *                                                             '-----------'
+ *                                                                called
+ *
+ * Most notably, if something is queued and the function is called again, we discard the
+ *   previously queued task completely.
+ */
+export class LatestQueue {
+  private isRunning: boolean;
+
+  private queuedTask?: () => Promise<void>;
+
+  private onceEmptyCallbacks: Array<() => unknown>;
+
+  constructor() {
+    this.isRunning = false;
+    this.onceEmptyCallbacks = [];
+  }
+
+  /**
+   * Does one of the following:
+   *
+   * 1. Runs the task immediately.
+   * 2. Enqueues the task, destroying any previously-enqueued task. In other words, 0 or 1
+   *    tasks will be enqueued at a time.
+   */
+  add(task: () => Promise<void>): void {
+    if (this.isRunning) {
+      this.queuedTask = task;
+    } else {
+      this.isRunning = true;
+      task().finally(() => {
+        this.isRunning = false;
+
+        const { queuedTask } = this;
+        if (queuedTask) {
+          this.queuedTask = undefined;
+          this.add(queuedTask);
+        } else {
+          try {
+            this.onceEmptyCallbacks.forEach(callback => {
+              callback();
+            });
+          } finally {
+            this.onceEmptyCallbacks = [];
+          }
+        }
+      });
+    }
+  }
+
+  /**
+   * Adds a callback to be called the first time the queue goes from "running" to "empty".
+   */
+  onceEmpty(callback: () => unknown): void {
+    this.onceEmptyCallbacks.push(callback);
+  }
+}

ts/util/lint/exceptions.json

@@ -14728,7 +14728,7 @@
     "rule": "React-createRef",
     "path": "ts/components/conversation/ConversationHeader.js",
     "line": "        this.menuTriggerRef = react_1.default.createRef();",
-    "lineNumber": 28,
+    "lineNumber": 29,
     "reasonCategory": "usageTrusted",
     "updated": "2020-08-28T16:12:19.904Z",
     "reasonDetail": "Used to reference popup menu"
@@ -14737,7 +14737,7 @@
     "rule": "React-createRef",
     "path": "ts/components/conversation/ConversationHeader.tsx",
     "line": "    this.menuTriggerRef = React.createRef();",
-    "lineNumber": 100,
+    "lineNumber": 101,
     "reasonCategory": "usageTrusted",
     "updated": "2020-05-20T20:10:43.540Z",
     "reasonDetail": "Used to reference popup menu"