Nav pill slide animation (#39)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/shell/BottomBar.test.tsx

@@ -0,0 +1,282 @@
+import { fireEvent, render, screen, within } from '@testing-library/react'
+import { MemoryRouter } from 'react-router'
+import { afterEach, beforeEach, describe, expect, it, vi, type Mock } from 'vitest'
+import App from '../App.tsx'
+import { declaredStyle } from '../test/cssRules.ts'
+import { mockViewport } from '../test/matchMedia.ts'
+import styles from './BottomBar.module.css'
+
+const MOBILE = 390
+const SPRING = 'cubic-bezier(.34, 1.4, .64, 1)'
+
+// jsdom does no layout, so lay the bar out here: items sit side by side from
+// 6 px in, inactive items 48 px wide and the active one (icon + label) 110 px.
+function layOut(element: HTMLElement): { left: number; width: number } {
+  const bar = element.parentElement!
+  const items = Array.from(bar.querySelectorAll<HTMLElement>(`.${styles.item}`))
+  let left = 6
+  for (const item of items) {
+    const width = item.getAttribute('aria-current') === 'page' ? 110 : 48
+    if (item === element) return { left, width }
+    left += width
+  }
+  return { left: 0, width: 0 }
+}
+
+// jsdom paints nothing either, so bounding boxes come from the laid-out
+// offsets with the bar at the viewport's left edge. A test mid-slide sets
+// where the pill is drawn and how far each item is still translated.
+let drawnPill: { left: number; width: number } | null
+let translated: Map<Element, number>
+
+function box(left: number, width: number): DOMRect {
+  return { left, width, x: left, right: left + width, top: 0, y: 0, bottom: 0, height: 0 } as DOMRect
+}
+
+let animate: Mock<Element['animate']>
+
+beforeEach(() => {
+  drawnPill = null
+  translated = new Map()
+  // jsdom has no Web Animations API.
+  animate = vi.fn<Element['animate']>(() => ({ cancel: vi.fn() }) as unknown as Animation)
+  Element.prototype.animate = animate
+  vi.spyOn(Element.prototype, 'getBoundingClientRect').mockImplementation(function (this: Element) {
+    if (!(this instanceof HTMLElement)) return box(0, 0)
+    if (this.classList.contains(styles.pill!)) {
+      return drawnPill
+        ? box(drawnPill.left, drawnPill.width)
+        : box(parseFloat(this.style.left), parseFloat(this.style.width))
+    }
+    if (this.classList.contains(styles.item!)) {
+      return box(this.offsetLeft + (translated.get(this) ?? 0), this.offsetWidth)
+    }
+    return box(0, 0)
+  })
+  vi.spyOn(HTMLElement.prototype, 'offsetLeft', 'get').mockImplementation(function (this: HTMLElement) {
+    return layOut(this).left
+  })
+  vi.spyOn(HTMLElement.prototype, 'offsetWidth', 'get').mockImplementation(function (this: HTMLElement) {
+    return layOut(this).width
+  })
+})
+
+afterEach(() => {
+  vi.restoreAllMocks()
+  Reflect.deleteProperty(Element.prototype, 'animate')
+  Reflect.deleteProperty(window, 'matchMedia')
+})
+
+function renderAt(path: string, reducedMotion = false) {
+  mockViewport(MOBILE, { reducedMotion })
+  render(
+    <MemoryRouter initialEntries={[path]}>
+      <App />
+    </MemoryRouter>,
+  )
+}
+
+function nav() {
+  return screen.getByRole('navigation', { name: 'Primary' })
+}
+
+function pill(): HTMLElement {
+  return nav().querySelector<HTMLElement>(`.${styles.pill}`)!
+}
+
+function link(name: string): HTMLElement {
+  return within(nav()).getByRole('link', { name })
+}
+
+function runningOn(element: Element): Animation[] {
+  return animate.mock.contexts
+    .map((target, i) => ({ target, animation: animate.mock.results[i]!.value as Animation }))
+    .filter(({ target }) => target === element)
+    .map(({ animation }) => animation)
+}
+
+function animationsOf(element: Element) {
+  return animate.mock.contexts
+    .map((target, i) => ({ target, args: animate.mock.calls[i]! }))
+    .filter(({ target }) => target === element)
+    .map(({ args }) => ({ keyframes: args[0], options: args[1] as KeyframeAnimationOptions }))
+}
+
+describe('BottomBar', () => {
+  it('places the pill on the active item without animating on first render', () => {
+    renderAt('/plan')
+    expect(pill().style.left).toBe('54px')
+    expect(pill().style.width).toBe('110px')
+    expect(pill()).toBeVisible()
+    expect(animate).not.toHaveBeenCalled()
+  })
+
+  it('hides the pill when no item is active', () => {
+    renderAt('/onboarding')
+    expect(pill()).not.toBeVisible()
+  })
+
+  it('slides the pill from the old item to the new one over 420 ms on the spring curve', () => {
+    renderAt('/')
+    fireEvent.click(link('Quick'))
+
+    expect(animationsOf(pill())).toEqual([
+      {
+        keyframes: [
+          { left: '6px', width: '110px' },
+          { left: '150px', width: '110px' },
+        ],
+        options: { duration: 420, easing: SPRING },
+      },
+    ])
+    expect(pill().style.left).toBe('150px')
+    expect(pill().style.width).toBe('110px')
+  })
+
+  it('FLIPs every item that moved from its old left to its new one with the same timing', () => {
+    renderAt('/')
+    fireEvent.click(link('Quick'))
+
+    // Home shrinks from 110 to 48 px, so Plan and Discover shift 62 px left
+    // and Quick grows in place; Settings ends where it started.
+    for (const name of ['Plan', 'Discover']) {
+      expect(animationsOf(link(name))).toEqual([
+        {
+          keyframes: [{ transform: 'translateX(62px)' }, { transform: 'translateX(0)' }],
+          options: { duration: 420, easing: SPRING },
+        },
+      ])
+    }
+    expect(animationsOf(link('Quick'))).toEqual([
+      {
+        keyframes: [{ transform: 'translateX(62px)' }, { transform: 'translateX(0)' }],
+        options: { duration: 420, easing: SPRING },
+      },
+    ])
+    expect(animationsOf(link('Home'))).toEqual([])
+    expect(animationsOf(link('Settings'))).toEqual([])
+  })
+
+  it('fades the new label in over 220 ms ease-out after 120 ms', () => {
+    renderAt('/')
+    fireEvent.click(link('Discover'))
+
+    const label = within(link('Discover')).getByText('Discover')
+    expect(label).toHaveClass(styles.label!)
+    expect(animationsOf(label)).toEqual([
+      {
+        keyframes: [
+          { opacity: 0, transform: 'translateX(-4px)' },
+          { opacity: 1, transform: 'none' },
+        ],
+        options: { duration: 220, delay: 120, easing: 'ease-out', fill: 'backwards' },
+      },
+    ])
+  })
+
+  it('does not animate when the active item stays the same', () => {
+    renderAt('/plan')
+    fireEvent.click(link('Plan'))
+    expect(animate).not.toHaveBeenCalled()
+  })
+
+  it('jumps the pill to the new item with no animation under reduced motion', () => {
+    renderAt('/', true)
+    fireEvent.click(link('Settings'))
+
+    expect(link('Settings')).toHaveAttribute('aria-current', 'page')
+    expect(animate).not.toHaveBeenCalled()
+    expect(pill().style.left).toBe('198px')
+    expect(pill().style.width).toBe('110px')
+  })
+
+  it('re-places the pill when the viewport resizes', () => {
+    renderAt('/discover')
+    expect(pill().style.left).toBe('102px')
+    vi.spyOn(HTMLElement.prototype, 'offsetLeft', 'get').mockReturnValue(120)
+    vi.spyOn(HTMLElement.prototype, 'offsetWidth', 'get').mockReturnValue(96)
+    fireEvent(window, new Event('resize'))
+    expect(pill().style.left).toBe('120px')
+    expect(pill().style.width).toBe('96px')
+    expect(animate).not.toHaveBeenCalled()
+  })
+
+  it('starts a second slide from where the first one is on screen, not from its destination', () => {
+    renderAt('/')
+    fireEvent.click(link('Quick'))
+    const [firstPill] = runningOn(pill())
+    const firstPlan = runningOn(link('Plan'))[0]!
+
+    // Midway: the pill is drawn at 78 px on its way from 6 to 150, and Plan
+    // still carries 31 of its 62 px FLIP translation.
+    drawnPill = { left: 78, width: 110 }
+    translated.set(link('Plan'), 31)
+    animate.mockClear()
+    fireEvent.click(link('Settings'))
+
+    expect(firstPill!.cancel).toHaveBeenCalled()
+    expect(firstPlan.cancel).toHaveBeenCalled()
+    expect(animationsOf(pill())).toEqual([
+      {
+        keyframes: [
+          { left: '78px', width: '110px' },
+          { left: '198px', width: '110px' },
+        ],
+        options: { duration: 420, easing: SPRING },
+      },
+    ])
+    // Plan's layout does not move between Quick and Settings, so it only
+    // finishes the 31 px it had left. Settings moves 62 px left.
+    expect(animationsOf(link('Plan'))).toEqual([
+      {
+        keyframes: [{ transform: 'translateX(31px)' }, { transform: 'translateX(0)' }],
+        options: { duration: 420, easing: SPRING },
+      },
+    ])
+    expect(animationsOf(link('Settings'))).toEqual([
+      {
+        keyframes: [{ transform: 'translateX(62px)' }, { transform: 'translateX(0)' }],
+        options: { duration: 420, easing: SPRING },
+      },
+    ])
+  })
+
+  it('stops a running slide and places the pill on the active item when the viewport resizes', () => {
+    renderAt('/')
+    fireEvent.click(link('Quick'))
+    const slide = [pill(), link('Plan'), link('Discover'), link('Quick')].flatMap(runningOn)
+    expect(slide).toHaveLength(4)
+
+    animate.mockClear()
+    vi.spyOn(HTMLElement.prototype, 'offsetLeft', 'get').mockReturnValue(140)
+    vi.spyOn(HTMLElement.prototype, 'offsetWidth', 'get').mockReturnValue(96)
+    fireEvent(window, new Event('resize'))
+
+    for (const animation of slide) expect(animation.cancel).toHaveBeenCalled()
+    expect(animate).not.toHaveBeenCalled()
+    expect(pill().style.left).toBe('140px')
+    expect(pill().style.width).toBe('96px')
+  })
+
+  it('re-places the pill once the web fonts are ready', async () => {
+    let fontsReady!: () => void
+    const ready = new Promise<void>((resolve) => (fontsReady = resolve))
+    Object.defineProperty(document, 'fonts', { configurable: true, value: { ready } })
+    try {
+      renderAt('/discover')
+      vi.spyOn(HTMLElement.prototype, 'offsetWidth', 'get').mockReturnValue(124)
+      fontsReady()
+      await ready
+      expect(pill().style.width).toBe('124px')
+    } finally {
+      Reflect.deleteProperty(document, 'fonts')
+    }
+  })
+
+  it('crossfades the icon colour with a .2s colour transition', () => {
+    renderAt('/')
+    for (const item of within(nav()).getAllByRole('link')) {
+      expect(declaredStyle(item).transition).toBe('color .2s')
+    }
+  })
+})