From 8f8813a19a52e20d242b5017e109da6805d4d4b3 Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Sat, 24 Sep 2022 15:16:02 -0700
Subject: [PATCH] Add PriorityTaskQueue

---
 src/common/{Idle.ts => TaskQueue.ts} | 65 +++++++++++++++++++++++++---
 1 file changed, 58 insertions(+), 7 deletions(-)
 rename src/common/{Idle.ts => TaskQueue.ts} (54%)

diff --git a/src/common/Idle.ts b/src/common/TaskQueue.ts
similarity index 54%
rename from src/common/Idle.ts
rename to src/common/TaskQueue.ts
index e05ad068..49e3f5ec 100644
--- a/src/common/Idle.ts
+++ b/src/common/TaskQueue.ts
@@ -3,16 +3,24 @@
  * @license MIT
  */
 
-/**
- * A queue of that runs tasks over several idle callbacks, trying to maintain the specified
- * frame rate. The tasks will run in the order they are enqueued, but they will run some time later,
- * and care should be taken to ensure they're non-urgent and will not introduce race conditions.
- */
-export class IdleTaskQueue {
+import { isNode } from 'common/Platform';
+
+interface ITaskQueue {
+}
+
+interface ITaskDeadline {
+  timeRemaining(): number;
+}
+type CallbackWithDeadline = (deadline: ITaskDeadline) => void;
+
+abstract class TaskQueue implements ITaskQueue {
   private _tasks: (() => void)[] = [];
   private _idleCallback?: number;
   private _i = 0;
 
+  protected abstract _requestCallback(callback: CallbackWithDeadline): number;
+  protected abstract _cancelCallback(identifier: number): void;
+
   /**
    * Adds a task to the queue which will run in a future idle callback.
    */
@@ -69,12 +77,55 @@ export class IdleTaskQueue {
   }
 }
 
+/**
+ * A queue of that runs tasks over several tasks via setTimeout, trying to maintain above 60 frames
+ * per second. The tasks will run in the order they are enqueued, but they will run some time later,
+ * and care should be taken to ensure they're non-urgent and will not introduce race conditions.
+ */
+export class PriorityTaskQueue extends TaskQueue {
+  protected _requestCallback(callback: CallbackWithDeadline): number {
+    return setTimeout(() => callback(this._createDeadline(16)));
+  }
+
+  protected _cancelCallback(identifier: number): void {
+    clearTimeout(identifier);
+  }
+
+  private _createDeadline(duration: number): ITaskDeadline {
+    const end = performance.now() + duration;
+    return {
+      timeRemaining: () => Math.max(0, end - performance.now())
+    };
+  }
+}
+
+class IdleTaskQueueInternal extends TaskQueue {
+  protected _requestCallback(callback: IdleRequestCallback): number {
+    return requestIdleCallback(callback);
+  }
+
+  protected _cancelCallback(identifier: number): void {
+    cancelIdleCallback(identifier);
+  }
+}
+
+/**
+ * A queue of that runs tasks over several idle callbacks, trying to respect the idle callback's
+ * deadline given by the environment. The tasks will run in the order they are enqueued, but they
+ * will run some time later, and care should be taken to ensure they're non-urgent and will not
+ * introduce race conditions.
+ *
+ * This reverts to a {@link PriorityTaskQueue} if the environment does not support idle callbacks.
+ */
+// eslint-disable-next-line @typescript-eslint/naming-convention
+export const IdleTaskQueue = (!isNode && 'requestIdleCallback' in window) ? IdleTaskQueueInternal : PriorityTaskQueue;
+
 /**
  * An object that tracks a single debounced task that will run on the next idle frame. When called
  * multiple times, only the last set task will run.
  */
 export class DebouncedIdleTask {
-  private _queue: IdleTaskQueue;
+  private _queue: IdleTaskQueueInternal | PriorityTaskQueue;
 
   constructor() {
     this._queue = new IdleTaskQueue();