fix: Lazy unloading should not leave dangling connections (#2004)

- Closes #1992

tests/components-lib/lazy-load-controller.test.ts

@@ -0,0 +1,203 @@
+import {
+  afterAll,
+  afterEach,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+} from 'vitest';
+import { LazyLoadController } from '../../src/components-lib/lazy-load-controller';
+import { LazyUnloadCondition } from '../../src/config/schema/common/media-actions';
+import {
+  callIntersectionHandler,
+  callVisibilityHandler,
+  createLitElement,
+  getMockIntersectionObserver,
+  IntersectionObserverMock,
+} from '../test-utils';
+
+// @vitest-environment jsdom
+describe('LazyLoadController', () => {
+  beforeAll(() => {
+    vi.stubGlobal('IntersectionObserver', IntersectionObserverMock);
+  });
+
+  afterAll(() => {
+    vi.unstubAllGlobals();
+  });
+
+  beforeEach(() => {
+    vi.spyOn(global.document, 'addEventListener');
+    vi.spyOn(global.document, 'removeEventListener');
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('should be loaded by default', () => {
+    const controller = new LazyLoadController(createLitElement());
+    expect(controller.isLoaded()).toBe(true);
+  });
+
+  it('should not be loaded by default when lazy load is set to true', () => {
+    const controller = new LazyLoadController(createLitElement(), true);
+    expect(controller.isLoaded()).toBe(false);
+  });
+
+  it('should add controller to host', () => {
+    const host = createLitElement();
+    const controller = new LazyLoadController(host);
+    expect(host.addController).toBeCalledWith(controller);
+  });
+
+  it('should remove controller from host', () => {
+    const host = createLitElement();
+    const controller = new LazyLoadController(host);
+    controller.removeController();
+    expect(host.removeController).toBeCalledWith(controller);
+  });
+
+  it('should remove handlers and listeners on destroy', () => {
+    const controller = new LazyLoadController(createLitElement(), true, [
+      'unselected',
+      'hidden',
+    ]);
+    controller.hostConnected();
+
+    const listener = vi.fn();
+    controller.addListener(listener);
+
+    controller.destroy();
+
+    expect(getMockIntersectionObserver()?.disconnect).toBeCalled();
+    expect(global.document.removeEventListener).toBeCalledWith(
+      'visibilitychange',
+      expect.anything(),
+    );
+    expect(controller.isLoaded()).toBe(false);
+
+    callVisibilityHandler(true);
+    callIntersectionHandler(true);
+    expect(listener).not.toBeCalled();
+  });
+
+  describe('should lazy load', () => {
+    it('should load when both visible and intersecting', () => {
+      const controller = new LazyLoadController(createLitElement(), true);
+      controller.hostConnected();
+
+      expect(controller.isLoaded()).toBe(false);
+
+      callVisibilityHandler(true);
+      expect(controller.isLoaded()).toBe(false);
+
+      callIntersectionHandler(true);
+      expect(controller.isLoaded()).toBe(true);
+    });
+  });
+
+  describe('should lazy unload', () => {
+    it('should unload on DOM disconnection', () => {
+      const controller = new LazyLoadController(createLitElement());
+      controller.hostConnected();
+
+      expect(controller.isLoaded()).toBe(true);
+
+      controller.hostDisconnected();
+
+      expect(controller.isLoaded()).toBe(false);
+
+      // Should also stop observing.
+      expect(getMockIntersectionObserver()?.disconnect).toBeCalled();
+      expect(global.document.removeEventListener).toBeCalledWith(
+        'visibilitychange',
+        expect.anything(),
+      );
+    });
+
+    describe('should lazy unload when not visible', () => {
+      it.each([
+        [[], true],
+        [['unselected' as const], true],
+        [['hidden' as const], false],
+        [['unselected' as const, 'hidden' as const], false],
+      ])(
+        'when unload conditions are: %s',
+        (unloadConditions: LazyUnloadCondition[], shouldBeLoaded: boolean) => {
+          const controller = new LazyLoadController(
+            createLitElement(),
+            true,
+            unloadConditions,
+          );
+          controller.hostConnected();
+
+          callIntersectionHandler(true);
+          callVisibilityHandler(true);
+          expect(controller.isLoaded()).toBe(true);
+
+          callVisibilityHandler(false);
+          expect(controller.isLoaded()).toBe(shouldBeLoaded);
+        },
+      );
+    });
+
+    describe('should lazy unload when not intersecting', () => {
+      it.each([
+        [[], true],
+        [['unselected' as const], false],
+        [['hidden' as const], true],
+        [['unselected' as const, 'hidden' as const], false],
+      ])(
+        'when unload conditions are: %s',
+        (unloadConditions: LazyUnloadCondition[], shouldBeLoaded: boolean) => {
+          const controller = new LazyLoadController(
+            createLitElement(),
+            true,
+            unloadConditions,
+          );
+          controller.hostConnected();
+
+          callIntersectionHandler(true);
+          callVisibilityHandler(true);
+          expect(controller.isLoaded()).toBe(true);
+
+          callIntersectionHandler(false);
+          expect(controller.isLoaded()).toBe(shouldBeLoaded);
+        },
+      );
+    });
+  });
+
+  it('should call listeners', () => {
+    const listener = vi.fn();
+    const controller = new LazyLoadController(createLitElement(), true, [
+      'unselected',
+      'hidden',
+    ]);
+    controller.hostConnected();
+    controller.addListener(listener);
+
+    expect(controller.isLoaded()).toBe(false);
+
+    callIntersectionHandler(true);
+    callVisibilityHandler(true);
+    expect(listener).toHaveBeenLastCalledWith(true);
+    expect(listener).toBeCalledTimes(1);
+
+    callIntersectionHandler(false);
+    expect(listener).toHaveBeenLastCalledWith(false);
+    expect(listener).toBeCalledTimes(2);
+
+    callIntersectionHandler(true);
+    expect(listener).toHaveBeenLastCalledWith(true);
+    expect(listener).toBeCalledTimes(3);
+
+    controller.removeListener(listener);
+
+    callIntersectionHandler(false);
+    expect(listener).toBeCalledTimes(3);
+  });
+});