feat(packages/excalidraw): state tracking, api hook, and others (#10870)

packages/common/src/appEventBus.test.ts

@@ -0,0 +1,74 @@
+import { AppEventBus } from "./appEventBus";
+
+type TestEvents = {
+  initialize: [api: number];
+  pointerUp: [pointerId: string];
+  viewState: [zoom: number];
+};
+
+const behavior = {
+  initialize: { cardinality: "once", replay: "last" },
+  pointerUp: { cardinality: "many", replay: "none" },
+  viewState: { cardinality: "many", replay: "last" },
+} as const;
+
+const flushMicrotasks = async () => Promise.resolve();
+
+describe("AppEventBus", () => {
+  it("replays once events to late callback and Promise subscribers", async () => {
+    const bus = new AppEventBus<TestEvents, typeof behavior>(behavior);
+    bus.emit("initialize", 42);
+
+    const calls: number[] = [];
+    bus.on("initialize", (value) => {
+      calls.push(value);
+    });
+
+    expect(calls).toEqual([]);
+    await flushMicrotasks();
+    expect(calls).toEqual([42]);
+
+    await expect(bus.on("initialize")).resolves.toBe(42);
+  });
+
+  it("does not replay stream events to late subscribers", async () => {
+    const bus = new AppEventBus<TestEvents, typeof behavior>(behavior);
+    bus.emit("pointerUp", "first");
+
+    const calls: string[] = [];
+    bus.on("pointerUp", (pointerId) => {
+      calls.push(pointerId);
+    });
+
+    await flushMicrotasks();
+    expect(calls).toEqual([]);
+
+    bus.emit("pointerUp", "second");
+    expect(calls).toEqual(["second"]);
+  });
+
+  it("replays replay-last stream events and stays subscribed", async () => {
+    const bus = new AppEventBus<TestEvents, typeof behavior>(behavior);
+    bus.emit("viewState", 1);
+
+    const calls: number[] = [];
+    bus.on("viewState", (zoom) => {
+      calls.push(zoom);
+    });
+
+    await flushMicrotasks();
+    expect(calls).toEqual([1]);
+
+    bus.emit("viewState", 2);
+    expect(calls).toEqual([1, 2]);
+  });
+
+  it("throws when emitting a once event twice", () => {
+    const bus = new AppEventBus<TestEvents, typeof behavior>(behavior);
+    bus.emit("initialize", 1);
+
+    expect(() => {
+      bus.emit("initialize", 2);
+    }).toThrow('Event "initialize" can only be emitted once');
+  });
+});