docs/specs/frontend/37-4-app-integration.md

Spec 37.4: App Integration

Status: READY FOR IMPLEMENTATION Phase: 4 of 5 Depends On: Spec 37.3 (Interactive Components) Goal: Wire all components together into a working application

---

Deliverables

By the end of this phase, you will have:

1. Complete App.tsx with full user flow
2. Integration tests for the complete workflow
3. Error handling for all states
4. Working end-to-end flow (with mocked API)

---

Step 1: App Integration Tests

Create src/App.test.tsx:

import { describe, it, expect, vi } from 'vitest'
import { render, screen, waitFor } from '@testing-library/react'
import userEvent from '@testing-library/user-event'
import { server } from './mocks/server'
import { errorHandlers } from './mocks/handlers'
import App from './App'

describe('App Integration', () => {
  describe('Initial Render', () => {
    it('renders main heading', () => {
      render(<App />)

      expect(
        screen.getByRole('heading', { name: /stroke lesion segmentation/i })
      ).toBeInTheDocument()
    })

    it('renders case selector', async () => {
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })
    })

    it('renders run button', () => {
      render(<App />)

      expect(
        screen.getByRole('button', { name: /run segmentation/i })
      ).toBeInTheDocument()
    })

    it('shows placeholder viewer message', () => {
      render(<App />)

      expect(
        screen.getByText(/select a case and run segmentation/i)
      ).toBeInTheDocument()
    })
  })

  describe('Run Button State', () => {
    it('disables run button when no case selected', async () => {
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      expect(
        screen.getByRole('button', { name: /run segmentation/i })
      ).toBeDisabled()
    })

    it('enables run button when case selected', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')

      expect(
        screen.getByRole('button', { name: /run segmentation/i })
      ).toBeEnabled()
    })
  })

  describe('Segmentation Flow', () => {
    it('shows processing state when running', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      expect(screen.getByText(/processing/i)).toBeInTheDocument()
    })

    it('displays metrics after successful segmentation', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByText('0.847')).toBeInTheDocument()
      })

      expect(screen.getByText('15.32 mL')).toBeInTheDocument()
      expect(screen.getByText(/12\.5s/)).toBeInTheDocument()
    })

    it('displays viewer after successful segmentation', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(document.querySelector('canvas')).toBeInTheDocument()
      })
    })

    it('hides placeholder after successful segmentation', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByText('0.847')).toBeInTheDocument()
      })

      expect(
        screen.queryByText(/select a case and run segmentation/i)
      ).not.toBeInTheDocument()
    })
  })

  describe('Error Handling', () => {
    it('shows error when segmentation fails', async () => {
      server.use(errorHandlers.segmentServerError)
      const user = userEvent.setup()

      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByRole('alert')).toBeInTheDocument()
      })

      expect(screen.getByText(/segmentation failed/i)).toBeInTheDocument()
    })

    it('allows retry after error', async () => {
      server.use(errorHandlers.segmentServerError)
      const user = userEvent.setup()

      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByRole('alert')).toBeInTheDocument()
      })

      // Reset to success handler
      server.resetHandlers()

      // Retry
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByText('0.847')).toBeInTheDocument()
      })

      expect(screen.queryByRole('alert')).not.toBeInTheDocument()
    })
  })

  describe('Multiple Runs', () => {
    it('allows running segmentation on different cases', async () => {
      const user = userEvent.setup()
      render(<App />)

      await waitFor(() => {
        expect(screen.getByRole('combobox')).toBeInTheDocument()
      })

      // First case
      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0001')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByText('sub-stroke0001')).toBeInTheDocument()
      })

      // Second case
      await user.selectOptions(screen.getByRole('combobox'), 'sub-stroke0002')
      await user.click(screen.getByRole('button', { name: /run segmentation/i }))

      await waitFor(() => {
        expect(screen.getByText('sub-stroke0002')).toBeInTheDocument()
      })
    })
  })
})

---

Step 2: App Implementation

Replace src/App.tsx:

import { useState } from 'react'
import { Layout } from './components/Layout'
import { CaseSelector } from './components/CaseSelector'
import { NiiVueViewer } from './components/NiiVueViewer'
import { MetricsPanel } from './components/MetricsPanel'
import { useSegmentation } from './hooks/useSegmentation'

export default function App() {
  const [selectedCase, setSelectedCase] = useState<string | null>(null)
  const { result, isLoading, error, runSegmentation } = useSegmentation()

  const handleRunSegmentation = async () => {
    if (selectedCase) {
      await runSegmentation(selectedCase)
    }
  }

  return (
    <Layout>
      <div className="grid grid-cols-1 lg:grid-cols-3 gap-6">
        {/* Left Panel: Controls */}
        <div className="space-y-4">
          <CaseSelector
            selectedCase={selectedCase}
            onSelectCase={setSelectedCase}
          />

          <button
            onClick={handleRunSegmentation}
            disabled={!selectedCase || isLoading}
            className="w-full bg-blue-600 hover:bg-blue-700 disabled:bg-gray-600
                       disabled:cursor-not-allowed text-white font-medium
                       py-3 px-4 rounded-lg transition-colors"
          >
            {isLoading ? 'Processing...' : 'Run Segmentation'}
          </button>

          {error && (
            <div role="alert" className="bg-red-900/50 text-red-300 p-3 rounded-lg">
              {error}
            </div>
          )}

          {result && <MetricsPanel metrics={result.metrics} />}
        </div>

        {/* Right Panel: Viewer */}
        <div className="lg:col-span-2">
          {result ? (
            <NiiVueViewer
              backgroundUrl={result.dwiUrl}
              overlayUrl={result.predictionUrl}
            />
          ) : (
            <div className="bg-gray-900 rounded-lg h-[500px] flex items-center justify-center">
              <p className="text-gray-400">
                Select a case and run segmentation to view results
              </p>
            </div>
          )}
        </div>
      </div>
    </Layout>
  )
}

---

Step 3: Run Tests

npm test
# Expected: ~45+ tests passing

---

Step 4: Visual Verification

npm run dev
# Open http://localhost:5173

Manual Test Checklist:

1. Page loads with header
2. Case selector shows "Loading cases..."
3. Case selector populates with 3 cases
4. Run button is disabled initially
5. Selecting a case enables run button
6. Clicking run shows "Processing..."
7. After completion, metrics panel appears
8. After completion, viewer shows (with demo image)
9. Selecting different case and running updates results

---

Step 5: Test Custom Render Utility (Optional Enhancement)

Create src/test/test-utils.tsx:

import type { ReactElement, ReactNode } from 'react'
import { render, RenderOptions } from '@testing-library/react'
import userEvent from '@testing-library/user-event'

// Wrapper for any providers (Router, Theme, etc.)
function AllTheProviders({ children }: { children: ReactNode }) {
  return <>{children}</>
}

function customRender(
  ui: ReactElement,
  options?: Omit<RenderOptions, 'wrapper'>
) {
  return {
    user: userEvent.setup(),
    ...render(ui, { wrapper: AllTheProviders, ...options }),
  }
}

// Re-export everything
export * from '@testing-library/react'
export { customRender as render }

Update tests to use custom render (optional):

import { render, screen, waitFor } from '../test/test-utils'
// Now `render` returns `{ user, ...result }`

---

Verification Checklist

# All tests pass
npm test
# Expected: ~45+ tests passing

# Build succeeds
npm run build
# Expected: dist/ folder created

# No TypeScript errors
npx tsc --noEmit
# Expected: No errors

• All integration tests pass
• Full flow works in browser
• Error states display correctly
• Loading states display correctly
• Results update on new runs

---

File Structure After This Phase

frontend/src/
├── components/
│   ├── __tests__/
│   │   ├── Layout.test.tsx
│   │   ├── MetricsPanel.test.tsx
│   │   ├── CaseSelector.test.tsx
│   │   └── NiiVueViewer.test.tsx
│   ├── Layout.tsx
│   ├── MetricsPanel.tsx
│   ├── CaseSelector.tsx
│   ├── NiiVueViewer.tsx
│   └── index.ts
├── api/
│   ├── __tests__/
│   │   └── client.test.ts
│   ├── client.ts
│   └── index.ts
├── hooks/
│   ├── __tests__/
│   │   └── useSegmentation.test.tsx
│   ├── useSegmentation.ts
│   └── index.ts
├── types/
│   └── index.ts
├── test/
│   ├── setup.ts
│   ├── fixtures.ts
│   └── test-utils.tsx
├── mocks/
│   ├── handlers.ts
│   └── server.ts
├── App.tsx
├── App.test.tsx
├── main.tsx
└── index.css

---

Next Phase

Once verification passes, proceed to Spec 37.5: E2E Tests & CI/CD