feat: finish the host-metrics plugin, move host status into core (B16)

plugins/host-metrics/tests/frontend/summary-store.test.ts

@@ -0,0 +1,56 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { createMetricsSummaryStore } from "../../src/frontend/summary-store";
+import type { HostMetricsApi } from "../../src/frontend/host-metrics-api";
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+function fakeApi() {
+  return {
+    registerViewer: vi.fn(async () => ({
+      success: true,
+      viewerSessionId: "v1",
+    })),
+    unregisterViewer: vi.fn(async () => undefined),
+    heartbeat: vi.fn(async () => true),
+    getMetrics: vi.fn(async () => ({ cpu: { percent: 5 } })),
+  };
+}
+
+const flush = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+describe("metrics summary store", () => {
+  it("holds one viewer per host while anything watches it", async () => {
+    const api = fakeApi();
+    const store = createMetricsSummaryStore(api as unknown as HostMetricsApi);
+    const listener = vi.fn();
+
+    const first = store.watch(7, listener);
+    const second = store.watch(7, vi.fn());
+    await flush();
+
+    expect(api.registerViewer).toHaveBeenCalledOnce();
+    expect(store.get(7)).toEqual({ cpu: { percent: 5 } });
+    expect(listener).toHaveBeenCalled();
+
+    first();
+    expect(api.unregisterViewer).not.toHaveBeenCalled();
+    second();
+    expect(api.unregisterViewer).toHaveBeenCalledWith(7, "v1");
+    expect(store.get(7)).toBeNull();
+  });
+
+  it("registers again when the server dropped the viewer", async () => {
+    vi.useFakeTimers();
+    const api = fakeApi();
+    const store = createMetricsSummaryStore(api as unknown as HostMetricsApi);
+    store.watch(7, vi.fn());
+    await vi.advanceTimersByTimeAsync(0);
+
+    api.heartbeat.mockResolvedValueOnce(false);
+    await vi.advanceTimersByTimeAsync(30_000);
+    expect(api.registerViewer).toHaveBeenCalledTimes(2);
+    store.dispose();
+  });
+});