feat(components/core): add scroll shadow directive

libs/components/core/src/index.ts

@@ -94,6 +94,9 @@ export { SkyResizeObserverService } from './lib/modules/resize-observer/resize-o
 
 export { SkyScreenReaderLabelDirective } from './lib/modules/screen-reader-label/screen-reader-label.directive';
 
+export { SkyScrollShadowDirective } from './lib/modules/scroll-shadow/scroll-shadow.directive';
+export { SkyScrollShadowEventArgs } from './lib/modules/scroll-shadow/scroll-shadow-event-args';
+
 export { SkyScrollableHostService } from './lib/modules/scrollable-host/scrollable-host.service';
 
 export { SkyStackingContext } from './lib/modules/stacking-context/stacking-context';

libs/components/core/src/lib/modules/scroll-shadow/fixtures/scroll-shadow.component.fixture.html

@@ -0,0 +1,26 @@
+<div class="scroll-shadow-test-wrapper">
+  <div
+    class="scroll-shadow-test-header"
+    [ngStyle]="{
+'box-shadow': scrollShadow?.topShadow ?? 'none'
+}"
+  ></div>
+  <div
+    class="scroll-shadow-test-body"
+    (skyScrollShadow)="scrollShadowChange($event)"
+    [skyScrollShadowEnabled]="enabled"
+  >
+    <span
+      class="scroll-shadow-test-content"
+      [ngStyle]="{
+    'height.px': height
+  }"
+    ></span>
+  </div>
+  <div
+    class="scroll-shadow-test-footer"
+    [ngStyle]="{
+  'box-shadow': scrollShadow?.bottomShadow ?? 'none'
+}"
+  ></div>
+</div>

libs/components/core/src/lib/modules/scroll-shadow/fixtures/scroll-shadow.component.fixture.scss

@@ -0,0 +1,17 @@
+:is(.scroll-shadow-test-header, .scroll-shadow-test-footer) {
+  height: 100px;
+}
+
+.scroll-shadow-test-body {
+  overflow-y: scroll;
+  display: block;
+  max-height: calc(100vh - 200px);
+}
+
+.scroll-shadow-test-content {
+  display: block;
+}
+
+.scroll-shadow-test-wrapper {
+  max-height: 100vh;
+}

libs/components/core/src/lib/modules/scroll-shadow/fixtures/scroll-shadow.component.fixture.ts

@@ -0,0 +1,25 @@
+import { CommonModule } from '@angular/common';
+import { ChangeDetectorRef, Component, inject } from '@angular/core';
+
+import { SkyScrollShadowEventArgs } from '../scroll-shadow-event-args';
+import { SkyScrollShadowDirective } from '../scroll-shadow.directive';
+
+@Component({
+  selector: 'sky-scroll-shadow-fixture',
+  styleUrls: ['./scroll-shadow.component.fixture.scss'],
+  templateUrl: './scroll-shadow.component.fixture.html',
+  imports: [CommonModule, SkyScrollShadowDirective],
+  standalone: true,
+})
+export class ScrollShadowFixtureComponent {
+  public enabled = true;
+  public height = 400;
+  public scrollShadow: SkyScrollShadowEventArgs | undefined;
+
+  #changeDetector = inject(ChangeDetectorRef);
+
+  public scrollShadowChange(args: SkyScrollShadowEventArgs): void {
+    this.scrollShadow = args;
+    this.#changeDetector.markForCheck();
+  }
+}

libs/components/modals/src/lib/modules/modal/modal-scroll-shadow-event-args.ts → libs/components/core/src/lib/modules/scroll-shadow/scroll-shadow-event-args.ts

@@ -1,7 +1,7 @@
 /**
  * @internal
  */
-export interface SkyModalScrollShadowEventArgs {
+export interface SkyScrollShadowEventArgs {
   bottomShadow: string;
 
   topShadow: string;

libs/components/core/src/lib/modules/scroll-shadow/scroll-shadow.directive.spec.ts

@@ -0,0 +1,180 @@
+import {
+  ComponentFixture,
+  TestBed,
+  fakeAsync,
+  tick,
+} from '@angular/core/testing';
+import { SkyAppTestUtility } from '@skyux-sdk/testing';
+
+import { ScrollShadowFixtureComponent } from './fixtures/scroll-shadow.component.fixture';
+
+// Wait for the next change detection cycle. This avoids having nested setTimeout() calls
+// and using the Jasmine done() function.
+function waitForMutationObserver(): Promise<void> {
+  return new Promise<void>((resolve) => {
+    setTimeout(() => resolve());
+  });
+}
+
+describe('Scroll shadow directive', () => {
+  function getScrollBody(): HTMLElement | null {
+    return document.querySelector<HTMLElement>('.scroll-shadow-test-body');
+  }
+
+  function getScrollFooter(): HTMLElement | null {
+    return document.querySelector<HTMLElement>('.scroll-shadow-test-footer');
+  }
+
+  function getScrollHeader(): HTMLElement | null {
+    return document.querySelector<HTMLElement>('.scroll-shadow-test-header');
+  }
+
+  function scrollElement(element: HTMLElement | null, yDistance: number): void {
+    if (element) {
+      element.scrollTop = yDistance;
+      SkyAppTestUtility.fireDomEvent(element, 'scroll');
+      fixture.detectChanges();
+    }
+  }
+
+  function validateShadow(
+    el: HTMLElement | null,
+    expectedAlpha?: number,
+  ): void {
+    if (!el) {
+      fail('Element not provided');
+      return;
+    }
+
+    const boxShadowStyle = getComputedStyle(el).boxShadow;
+
+    if (expectedAlpha) {
+      const rgbaMatch = boxShadowStyle.match(
+        /rgba\(0,\s*0,\s*0,\s*([0-9.]*)\)/,
+      );
+
+      if (!(rgbaMatch && rgbaMatch[1])) {
+        fail('No shadow found');
+      } else {
+        const alpha = parseFloat(rgbaMatch[1]);
+
+        expect(expectedAlpha).toBeCloseTo(alpha, 2);
+      }
+    } else {
+      expect(boxShadowStyle).toBe('none');
+    }
+  }
+
+  let fixture: ComponentFixture<ScrollShadowFixtureComponent>;
+  let cmp: ScrollShadowFixtureComponent;
+
+  beforeEach(fakeAsync(() => {
+    TestBed.configureTestingModule({
+      imports: [ScrollShadowFixtureComponent],
+    });
+
+    fixture = TestBed.createComponent(ScrollShadowFixtureComponent);
+    cmp = fixture.componentInstance;
+    fixture.detectChanges();
+    tick();
+    fixture.detectChanges();
+  }));
+
+  it('should not show a shadow when the body is not scrollable when disabled', async () => {
+    cmp.enabled = false;
+    fixture.detectChanges();
+    await waitForMutationObserver();
+    fixture.detectChanges();
+
+    validateShadow(getScrollFooter());
+    validateShadow(getScrollHeader());
+  });
+
+  it('should not show a shadow when the body is scrollable when disabled', async () => {
+    cmp.height = 800;
+    cmp.enabled = false;
+    fixture.detectChanges();
+    await waitForMutationObserver();
+    fixture.detectChanges();
+
+    validateShadow(getScrollFooter());
+    validateShadow(getScrollHeader());
+  });
+
+  it('should not show a shadow when the body is not scrollable', async () => {
+    await waitForMutationObserver();
+    fixture.detectChanges();
+
+    validateShadow(getScrollFooter());
+    validateShadow(getScrollHeader());
+  });
+
+  it('should progressively show a drop shadow as the modal content scrolls', async () => {
+    const headerEl = getScrollHeader();
+    const contentEl = getScrollBody();
+    const footerEl = getScrollFooter();
+
+    if (!contentEl) {
+      fail('Content element not found');
+      return;
+    }
+
+    cmp.height = 800;
+    fixture.detectChanges();
+    await waitForMutationObserver();
+    fixture.detectChanges();
+
+    scrollElement(contentEl, 0);
+    validateShadow(headerEl);
+    validateShadow(footerEl, 0.3);
+
+    scrollElement(contentEl, 15);
+    validateShadow(headerEl, 0.15);
+    validateShadow(footerEl, 0.3);
+
+    scrollElement(contentEl, 30);
+    validateShadow(headerEl, 0.3);
+    validateShadow(footerEl, 0.3);
+
+    scrollElement(contentEl, 31);
+    validateShadow(headerEl, 0.3);
+    validateShadow(footerEl, 0.3);
+
+    scrollElement(
+      contentEl,
+      contentEl.scrollHeight - 15 - contentEl.clientHeight,
+    );
+    validateShadow(headerEl, 0.3);
+    validateShadow(footerEl, 0.15);
+
+    scrollElement(contentEl, contentEl.scrollHeight - contentEl.clientHeight);
+    validateShadow(headerEl, 0.3);
+    validateShadow(footerEl);
+  });
+
+  it('should update the shadow on window resize', async () => {
+    const headerEl = getScrollHeader();
+    const contentEl = getScrollBody();
+    const footerEl = getScrollFooter();
+
+    if (!contentEl) {
+      fail('Content element not found');
+      return;
+    }
+
+    cmp.height = 800;
+    fixture.detectChanges();
+    await waitForMutationObserver();
+    fixture.detectChanges();
+
+    validateShadow(headerEl);
+    validateShadow(footerEl, 0.3);
+
+    spyOnProperty(Element.prototype, 'scrollTop').and.returnValue(15);
+    SkyAppTestUtility.fireDomEvent(window, 'resize');
+    fixture.detectChanges();
+
+    validateShadow(headerEl, 0.15);
+    validateShadow(footerEl, 0.3);
+  });
+});