// ✅ GOOD: Descriptive names
const marketSearchQuery = "election";
const isUserAuthenticated = true;
const totalRevenue = 1000;

// ❌ BAD: Unclear names
const q = "election";
const flag = true;
const x = 1000;

Function Naming

// ✅ GOOD: Verb-noun pattern
async function fetchMarketData(marketId: string) {}
function calculateSimilarity(a: number[], b: number[]) {}
function isValidEmail(email: string): boolean {}

// ❌ BAD: Unclear or noun-only
async function market(id: string) {}
function similarity(a, b) {}
function email(e) {}

Immutability Pattern (CRITICAL)

// ✅ ALWAYS use spread operator
const updatedUser = {
  ...user,
  name: "New Name",
};

const updatedArray = [...items, newItem];

// ❌ NEVER mutate directly
user.name = "New Name"; // BAD
items.push(newItem); // BAD

Error Handling

// ✅ GOOD: Comprehensive error handling
async function fetchData(url: string) {
  try {
    const response = await fetch(url);

    if (!response.ok) {
      throw new Error(`HTTP ${response.status}: ${response.statusText}`);
    }

    return await response.json();
  } catch (error) {
    console.error("Fetch failed:", error);
    throw new Error("Failed to fetch data");
  }
}

// ❌ BAD: No error handling
async function fetchData(url) {
  const response = await fetch(url);
  return response.json();
}

Async/Await Best Practices

// ✅ GOOD: Parallel execution when possible
const [users, markets, stats] = await Promise.all([fetchUsers(), fetchMarkets(), fetchStats()]);

// ❌ BAD: Sequential when unnecessary
const users = await fetchUsers();
const markets = await fetchMarkets();
const stats = await fetchStats();

Type Safety

// ✅ GOOD: Proper types
interface Market {
  id: string;
  name: string;
  status: "active" | "resolved" | "closed";
  created_at: Date;
}

function getMarket(id: string): Promise<Market> {
  // Implementation
}

// ❌ BAD: Using 'any'
function getMarket(id: any): Promise<any> {
  // Implementation
}

React Best Practices

Component Structure

// ✅ GOOD: Functional component with types
interface ButtonProps {
  children: React.ReactNode
  onClick: () => void
  disabled?: boolean
  variant?: 'primary' | 'secondary'
}

export function Button({
  children,
  onClick,
  disabled = false,
  variant = 'primary'
}: ButtonProps) {
  return (
    <button
      onClick={onClick}
      disabled={disabled}
      className={`btn btn-${variant}`}
    >
      {children}
    </button>
  )
}

// ❌ BAD: No types, unclear structure
export function Button(props) {
  return <button onClick={props.onClick}>{props.children}</button>
}

Custom Hooks

// ✅ GOOD: Reusable custom hook
export function useDebounce<T>(value: T, delay: number): T {
  const [debouncedValue, setDebouncedValue] = useState<T>(value);

  useEffect(() => {
    const handler = setTimeout(() => {
      setDebouncedValue(value);
    }, delay);

    return () => clearTimeout(handler);
  }, [value, delay]);

  return debouncedValue;
}

// Usage
const debouncedQuery = useDebounce(searchQuery, 500);

State Management

// ✅ GOOD: Proper state updates
const [count, setCount] = useState(0);

// Functional update for state based on previous state
setCount((prev) => prev + 1);

// ❌ BAD: Direct state reference
setCount(count + 1); // Can be stale in async scenarios

Conditional Rendering

// ✅ GOOD: Clear conditional rendering
{isLoading && <Spinner />}
{error && <ErrorMessage error={error} />}
{data && <DataDisplay data={data} />}

// ❌ BAD: Ternary hell
{isLoading ? <Spinner /> : error ? <ErrorMessage error={error} /> : data ? <DataDisplay data={data} /> : null}

API Design Standards

REST API Conventions

GET    /api/markets              # List all markets
GET    /api/markets/:id          # Get specific market
POST   /api/markets              # Create new market
PUT    /api/markets/:id          # Update market (full)
PATCH  /api/markets/:id          # Update market (partial)
DELETE /api/markets/:id          # Delete market

# Query parameters for filtering
GET /api/markets?status=active&limit=10&offset=0

Response Format

// ✅ GOOD: Consistent response structure
interface ApiResponse<T> {
  success: boolean;
  data?: T;
  error?: string;
  meta?: {
    total: number;
    page: number;
    limit: number;
  };
}

// Success response
return NextResponse.json({
  success: true,
  data: markets,
  meta: { total: 100, page: 1, limit: 10 },
});

// Error response
return NextResponse.json(
  {
    success: false,
    error: "Invalid request",
  },
  { status: 400 },
);

Input Validation

import { z } from "zod";

// ✅ GOOD: Schema validation
const CreateMarketSchema = z.object({
  name: z.string().min(1).max(200),
  description: z.string().min(1).max(2000),
  endDate: z.string().datetime(),
  categories: z.array(z.string()).min(1),
});

export async function POST(request: Request) {
  const body = await request.json();

  try {
    const validated = CreateMarketSchema.parse(body);
    // Proceed with validated data
  } catch (error) {
    if (error instanceof z.ZodError) {
      return NextResponse.json(
        {
          success: false,
          error: "Validation failed",
          details: error.errors,
        },
        { status: 400 },
      );
    }
  }
}

File Organization

Project Structure

src/
├── app/                    # Next.js App Router
│   ├── api/               # API routes
│   ├── markets/           # Market pages
│   └── (auth)/           # Auth pages (route groups)
├── components/            # React components
│   ├── ui/               # Generic UI components
│   ├── forms/            # Form components
│   └── layouts/          # Layout components
├── hooks/                # Custom React hooks
├── lib/                  # Utilities and configs
│   ├── api/             # API clients
│   ├── utils/           # Helper functions
│   └── constants/       # Constants
├── types/                # TypeScript types
└── styles/              # Global styles

File Naming

components/Button.tsx          # PascalCase for components
hooks/useAuth.ts              # camelCase with 'use' prefix
lib/formatDate.ts             # camelCase for utilities
types/market.types.ts         # camelCase with .types suffix

Comments & Documentation

When to Comment

// ✅ GOOD: Explain WHY, not WHAT
// Use exponential backoff to avoid overwhelming the API during outages
const delay = Math.min(1000 * Math.pow(2, retryCount), 30000);

// Deliberately using mutation here for performance with large arrays
items.push(newItem);

// ❌ BAD: Stating the obvious
// Increment counter by 1
count++;

// Set name to user's name
name = user.name;

JSDoc for Public APIs

/**
 * Searches markets using semantic similarity.
 *
 * @param query - Natural language search query
 * @param limit - Maximum number of results (default: 10)
 * @returns Array of markets sorted by similarity score
 * @throws {Error} If OpenAI API fails or Redis unavailable
 *
 * @example
 * ```typescript
 * const results = await searchMarkets('election', 5)
 * console.log(results[0].name) // "Trump vs Biden"
 * ```
 */
export async function searchMarkets(query: string, limit: number = 10): Promise<Market[]> {
  // Implementation
}

Performance Best Practices

Memoization

import { useMemo, useCallback } from "react";

// ✅ GOOD: Memoize expensive computations
const sortedMarkets = useMemo(() => {
  return markets.sort((a, b) => b.volume - a.volume);
}, [markets]);

// ✅ GOOD: Memoize callbacks
const handleSearch = useCallback((query: string) => {
  setSearchQuery(query);
}, []);

Lazy Loading

import { lazy, Suspense } from 'react'

// ✅ GOOD: Lazy load heavy components
const HeavyChart = lazy(() => import('./HeavyChart'))

export function Dashboard() {
  return (
    <Suspense fallback={<Spinner />}>
      <HeavyChart />
    </Suspense>
  )
}

Database Queries

// ✅ GOOD: Select only needed columns
const { data } = await supabase.from("markets").select("id, name, status").limit(10);

// ❌ BAD: Select everything
const { data } = await supabase.from("markets").select("*");

Testing Standards

Test Structure (AAA Pattern)

test("calculates similarity correctly", () => {
  // Arrange
  const vector1 = [1, 0, 0];
  const vector2 = [0, 1, 0];

  // Act
  const similarity = calculateCosineSimilarity(vector1, vector2);

  // Assert
  expect(similarity).toBe(0);
});

Test Naming

// ✅ GOOD: Descriptive test names
test("returns empty array when no markets match query", () => {});
test("throws error when OpenAI API key is missing", () => {});
test("falls back to substring search when Redis unavailable", () => {});

// ❌ BAD: Vague test names
test("works", () => {});
test("test search", () => {});

Code Smell Detection

Watch for these anti-patterns:

1. Long Functions

// ❌ BAD: Function > 50 lines
function processMarketData() {
  // 100 lines of code
}

// ✅ GOOD: Split into smaller functions
function processMarketData() {
  const validated = validateData();
  const transformed = transformData(validated);
  return saveData(transformed);
}

2. Deep Nesting

// ❌ BAD: 5+ levels of nesting
if (user) {
  if (user.isAdmin) {
    if (market) {
      if (market.isActive) {
        if (hasPermission) {
          // Do something
        }
      }
    }
  }
}

// ✅ GOOD: Early returns
if (!user) return;
if (!user.isAdmin) return;
if (!market) return;
if (!market.isActive) return;
if (!hasPermission) return;

// Do something

3. Magic Numbers

// ❌ BAD: Unexplained numbers
if (retryCount > 3) {
}
setTimeout(callback, 500);

// ✅ GOOD: Named constants
const MAX_RETRIES = 3;
const DEBOUNCE_DELAY_MS = 500;

if (retryCount > MAX_RETRIES) {
}
setTimeout(callback, DEBOUNCE_DELAY_MS);

Remember: Code quality is not negotiable. Clear, maintainable code enables rapid development and confident refactoring.