Agent skill

coding-standards

React 19 and TypeScript coding standards for Portfolio Buddy 2. Use when: writing new components, reviewing code, refactoring, or ensuring consistency. Contains component patterns, TypeScript rules, and best practices.

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SKILL.md

Coding Standards - Portfolio Buddy 2

React 19 Patterns

Component Structure

typescript
// Good: Functional component with TypeScript
interface MetricsTableProps {
  data: Metric[]
  onSelect: (id: string) => void
}

export function MetricsTable({ data, onSelect }: MetricsTableProps) {
  // Hooks at top
  const [selected, setSelected] = useState<Set<string>>(new Set())

  // Derived state with useMemo
  const sortedData = useMemo(() =>
    data.sort((a, b) => b.sharpe - a.sharpe),
    [data]
  )

  // Event handlers with useCallback
  const handleSelect = useCallback((id: string) => {
    setSelected(prev => new Set(prev).add(id))
    onSelect(id)
  }, [onSelect])

  // Render
  return <div>...</div>
}

Hooks Rules

  1. Only at top level - No hooks in conditionals or loops
  2. Custom hooks start with use - useMetrics, usePortfolio, useSorting
  3. Dependencies array complete - All deps in useEffect/useMemo/useCallback
  4. Cleanup on unmount - Return cleanup function from useEffect

State Management

Portfolio Buddy 2 uses PLAIN REACT HOOKS ONLY:

  • Local UI state → useState
  • Derived state → useMemo
  • Stable callbacks → useCallback
  • DOM/value refs → useRef

NO global state libraries:

  • ❌ No TanStack Query
  • ❌ No Zustand
  • ❌ No Redux
  • ❌ No Jotai

Pattern: Props down, custom hooks for shared logic

typescript
// State management example
const [files, setFiles] = useState<File[]>([])
const [dateRange, setDateRange] = useState({ start: null, end: null })

// Derived state
const filteredData = useMemo(() =>
  filterByDateRange(files, dateRange),
  [files, dateRange]
)

// Stable callback
const handleUpload = useCallback((newFile: File) => {
  setFiles(prev => [...prev, newFile])
}, [])

TypeScript Standards

No any Types

typescript
// Bad
const data: any = fetchData()

// Good
interface TradeData {
  symbol: string
  date: Date
  pnl: number
}
const data: TradeData[] = fetchData()

Current Violations (Tech Debt):

  • usePortfolio.ts: 11 instances (trade/metrics types)
  • useMetrics.ts: 4 instances (sort comparisons)
  • dataUtils.ts: 1 instance (Metrics interface)
  • Total: 15 violations to fix (originally 16)

Strict Null Checks

typescript
// Bad
const value = data.find(x => x.id === id)
value.name // Could be undefined!

// Good
const value = data.find(x => x.id === id)
if (value) {
  value.name // Type-safe
}

// Or with optional chaining
const name = data.find(x => x.id === id)?.name

Type Inference When Obvious

typescript
// Redundant
const count: number = 5
const name: string = 'Portfolio Buddy'

// Better (TypeScript infers)
const count = 5
const name = 'Portfolio Buddy'

// Explicit when needed
const metrics: Metric[] = [] // Empty array needs type

Component Size Limits

Max 200 Lines Per Component

When component exceeds 200 lines:

  1. Extract sub-components
  2. Move logic to custom hooks
  3. Extract utilities to utils/

Current Violations

⚠️ MUST REFACTOR:

  • PortfolioSection.tsx: 591 lines (295% of limit)
    • Extract EquityChartSection
    • Extract PortfolioStats
    • Extract ContractControls
    • Keep only orchestration logic

Should refactor:

  • App.tsx: 351 lines (175% of limit)
    • Extract sections into components
  • MetricsTable.tsx: 242 lines (121% of limit)
    • Improved from 350 lines, still over limit

Refactoring Example

typescript
// Before: 591 lines in PortfolioSection
function PortfolioSection() {
  // Contract multiplier logic (50 lines)
  // Date filtering logic (40 lines)
  // Chart configuration (100 lines)
  // Statistics calculation (80 lines)
  // Rendering logic (300+ lines)
}

// After: Split into focused pieces
function PortfolioSection() {
  const portfolio = usePortfolio(files, dateRange)
  const contracts = useContractMultipliers(portfolio.strategies)

  return (
    <div>
      <ContractControls {...contracts} />
      <EquityChartSection data={portfolio.equity} />
      <PortfolioStats metrics={portfolio.metrics} />
    </div>
  )
}

File Organization

Actual Directory Structure

src/
├── components/
│   └── [AllComponents].tsx    (flat structure, no subdirs)
├── hooks/
│   ├── useContractMultipliers.ts
│   ├── useMetrics.ts
│   ├── usePortfolio.ts
│   └── useSorting.ts
├── utils/
│   └── dataUtils.ts           (metric calculations, parsing)
├── App.tsx
└── main.tsx

Note: No ui/ or charts/ subdirectories - components are flat in components/

Naming Conventions

  • Components: PascalCase - MetricsTable.tsx, CorrelationHeatmap.tsx
  • Hooks: camelCase with use prefix - useMetrics.ts, useSorting.ts
  • Utils: camelCase - calculateMetrics(), parseCSV()
  • Types/Interfaces: PascalCase - interface Metric, type Trade

Error Handling

Always Handle Errors

typescript
// Bad
const data = await supabase.storage.upload(file)

// Good
const { data, error } = await supabase.storage.upload(file)
if (error) {
  console.error('Upload failed:', error)
  toast.error('Failed to upload file')
  return
}

Use Try-Catch for Parsing

typescript
// CSV parsing with error handling
try {
  const parsed = parseCSV(file)
  setData(parsed.data)
  if (parsed.errors.length > 0) {
    setErrors(parsed.errors)
  }
} catch (error) {
  console.error('Parse error:', error)
  toast.error('Invalid CSV format')
}

Error Boundaries

Current Status: No error boundaries implemented (tech debt)

Should add:

typescript
<ErrorBoundary fallback={<ErrorMessage />}>
  <PortfolioSection />
</ErrorBoundary>

Performance

Memoization

typescript
// Expensive calculations
const metrics = useMemo(
  () => calculateMetrics(portfolioData, riskFreeRate),
  [portfolioData, riskFreeRate]
)

// Large data transformations
const correlationMatrix = useMemo(
  () => buildCorrelationMatrix(selectedStrategies),
  [selectedStrategies]
)

Callback Stability

typescript
// Prevent child re-renders
const handleSort = useCallback((column: string) => {
  setSortColumn(column)
  setSortDirection(prev => prev === 'asc' ? 'desc' : 'asc')
}, [])

// Pass stable callback to children
<SortableHeader onSort={handleSort} />

Avoid Premature Optimization

  1. Build feature first
  2. Measure performance if issues arise
  3. Optimize based on profiling data
  4. Don't optimize without evidence

Chart.js Integration

Pattern for Chart Components

typescript
import { Line } from 'react-chartjs-2'
import { Chart as ChartJS, registerables } from 'chart.js'
import zoomPlugin from 'chartjs-plugin-zoom'

// Register plugins once
ChartJS.register(...registerables, zoomPlugin)

function EquityChart({ data }: { data: EquityData[] }) {
  const chartData = useMemo(() => ({
    labels: data.map(d => d.date),
    datasets: [{
      label: 'Equity',
      data: data.map(d => d.value),
      borderColor: 'rgb(75, 192, 192)',
    }]
  }), [data])

  const options = useMemo(() => ({
    responsive: true,
    plugins: {
      zoom: { enabled: true }
    }
  }), [])

  return <Line data={chartData} options={options} />
}

Chart Libraries

  • ✅ Use: Chart.js + react-chartjs-2
  • ❌ Don't use: Recharts (installed but unused, should remove)

Testing Standards

What to Test

  • ✅ Critical calculations (Sharpe, Sortino, correlation)
  • ✅ Data transformations (CSV parsing, metric calculations)
  • ✅ Error states and edge cases
  • ✅ Hook return values
  • ❌ UI implementation details (className, DOM structure)
  • ❌ Third-party library internals

Test Structure

typescript
describe('calculateMetrics', () => {
  it('calculates Sharpe ratio correctly', () => {
    const trades = mockTradeData()
    const result = calculateMetrics(trades, 0.02)
    expect(result.sharpe).toBeCloseTo(1.5, 2)
  })

  it('handles empty data gracefully', () => {
    const result = calculateMetrics([], 0.02)
    expect(result.sharpe).toBe(0)
  })
})

Current Status: No tests implemented (future work)

Import Organization

Order of Imports

typescript
// 1. React and external libraries
import { useState, useMemo, useCallback } from 'react'
import { Line } from 'react-chartjs-2'

// 2. Internal hooks
import { useMetrics } from '@/hooks/useMetrics'
import { usePortfolio } from '@/hooks/usePortfolio'

// 3. Utils and helpers
import { calculateMetrics, formatCurrency } from '@/utils/dataUtils'

// 4. Types
import type { Metric, Trade } from '@/types'

// 5. Styles (if any)
import './styles.css'

Code Comments

When to Comment

typescript
// Good: Explain WHY, not WHAT
// Annualize by multiplying by sqrt(252) trading days
const sharpe = (avgReturn / stdDev) * Math.sqrt(252)

// Bad: Obvious what the code does
// Calculate Sharpe ratio
const sharpe = (avgReturn / stdDev) * Math.sqrt(252)

JSDoc for Complex Functions

typescript
/**
 * Calculate Sortino Ratio using downside deviation
 * @param returns - Array of daily returns
 * @param riskFreeRate - Annual risk-free rate (e.g., 0.02 for 2%)
 * @param targetReturn - Target return threshold (default: 0)
 * @returns Annualized Sortino Ratio
 */
function calculateSortino(
  returns: number[],
  riskFreeRate: number,
  targetReturn = 0
): number {
  // Implementation
}

Git Commit Messages

Format

<type>: <subject>

<body>

Types

  • feat: New feature
  • fix: Bug fix
  • refactor: Code restructuring
  • perf: Performance improvement
  • docs: Documentation
  • test: Test additions/changes

Examples from Recent Commits

Fix Sortino Ratio calculation by annualizing downside deviation and correcting variance calculation

Refactor portfolio calculations and enhance Supabase client validation; add risk-free rate input and Sortino Ratio calculation

Enhance error handling and validation in Supabase data fetching; update MetricsTable and PortfolioSection to manage selectedTradeLists state

Code Review Checklist

Before submitting code:

  • TypeScript strict mode passes (no any unless documented as tech debt)
  • Component under 200 lines (or has refactor plan)
  • Error handling in place
  • Memoization for expensive calculations
  • Stable callbacks with useCallback
  • Proper TypeScript types (no any)
  • Imports organized by category
  • JSDoc on complex functions
  • Console.logs removed
  • Chart.js used (not Recharts)

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