feat: Add basic queue implementation

Author: HazAT

packages/core/src/queue.ts

@@ -0,0 +1,27 @@
+export class Queue<T> {
+  private queue: Set<Promise<T>> = new Set();
+
+  public add(task: Promise<T>): Promise<T> {
+    this.queue.add(task);
+    task.then(() => this.queue.delete(task));
+    return task;
+  }
+
+  public length(): number {
+    return this.queue.size;
+  }
+
+  public drain(timeout?: number): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const capturedSetTimeout = setTimeout(() => {
+        if (timeout && timeout > 0) {
+          reject('Drain timeout reached');
+        }
+      }, timeout);
+      Promise.all(this.queue.values()).then(() => {
+        clearTimeout(capturedSetTimeout);
+        resolve();
+      });
+    });
+  }
+}

packages/core/test/lib/queue.test.ts

@@ -0,0 +1,72 @@
+import { Queue } from '../../src/queue';
+
+describe('Queue', () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  test('add()', () => {
+    const q = new Queue<void>();
+    const p = new Promise<void>(resolve => setTimeout(resolve, 1));
+    q.add(p);
+    expect(q.length()).toBe(1);
+  });
+
+  test('resolved promises should not show up in queue length', async () => {
+    expect.assertions(2);
+    const q = new Queue<void>();
+    const p = new Promise<void>(resolve => setTimeout(resolve, 1));
+    q.add(p).then(() => {
+      expect(q.length()).toBe(0);
+    });
+    expect(q.length()).toBe(1);
+    jest.runAllTimers();
+  });
+
+  test('receive promise result outside and from queue', async () => {
+    expect.assertions(4);
+    const q = new Queue<string>();
+    const p = new Promise<string>(resolve =>
+      setTimeout(() => {
+        resolve('test');
+      }, 1),
+    );
+    q.add(p).then(result => {
+      expect(q.length()).toBe(0);
+      expect(result).toBe('test');
+    });
+    expect(q.length()).toBe(1);
+    p.then(result => {
+      expect(result).toBe('test');
+    });
+    jest.runAllTimers();
+  });
+
+  test('drain()', async () => {
+    expect.assertions(2);
+    const q = new Queue<void>();
+    for (let i = 0; i < 5; i++) {
+      const p = new Promise<void>(resolve => setTimeout(resolve, 1));
+      q.add(p);
+    }
+    expect(q.length()).toBe(5);
+    q.drain().then(() => {
+      expect(q.length()).toBe(0);
+    });
+    jest.runAllTimers();
+  });
+
+  test('drain() with timeout', async () => {
+    expect.assertions(2);
+    const q = new Queue<void>();
+    for (let i = 0; i < 5; i++) {
+      const p = new Promise<void>(resolve => setTimeout(resolve, 100));
+      q.add(p);
+    }
+    expect(q.length()).toBe(5);
+    q.drain(50).catch(e => {
+      expect(e).toBeTruthy();
+    });
+    jest.runAllTimers();
+  });
+});