pact-coding-standards

PACT Coding Standards

Clean code principles for the Code phase of PACT. This skill provides essential coding guidelines and links to detailed patterns for implementation.

Core Principles

1. Single Responsibility Principle

Each function, class, or module should have exactly one reason to change.

// BAD: Multiple responsibilities
class UserManager {
  createUser(data) { }
  validateEmail(email) { }
  sendWelcomeEmail(user) { }
  generateReport() { }
  updateUserPreferences(userId, prefs) { }
}

// GOOD: Single responsibility each
class UserService {
  createUser(data) { }
  updateUser(userId, data) { }
}

class EmailValidator {
  validate(email) { }
}

class NotificationService {
  sendWelcomeEmail(user) { }
}

class UserReportGenerator {
  generate(criteria) { }
}

2. DRY (Don't Repeat Yourself)

Extract duplicated logic into reusable functions.

// BAD: Duplicated validation logic
function createUser(data) {
  if (!data.email || !data.email.includes('@')) {
    throw new Error('Invalid email');
  }
  // ...
}

function updateUser(id, data) {
  if (data.email && !data.email.includes('@')) {
    throw new Error('Invalid email');
  }
  // ...
}

// GOOD: Extracted validation
function validateEmail(email) {
  if (!email || !email.includes('@')) {
    throw new ValidationError('Invalid email format');
  }
}

function createUser(data) {
  validateEmail(data.email);
  // ...
}

function updateUser(id, data) {
  if (data.email) {
    validateEmail(data.email);
  }
  // ...
}

3. KISS (Keep It Simple, Stupid)

Choose the simplest solution that works.

// BAD: Over-engineered
class ConfigurationFactoryBuilderManager {
  static getInstance() {
    return new ConfigurationFactoryBuilder()
      .withDefaults()
      .withEnvironment()
      .build()
      .getConfiguration();
  }
}

// GOOD: Simple and direct
const config = {
  port: process.env.PORT || 3000,
  dbUrl: process.env.DATABASE_URL,
  debug: process.env.NODE_ENV !== 'production'
};

4. Defensive Programming

Validate inputs, handle edge cases, and fail gracefully.

function processOrder(order) {
  // Guard clauses
  if (!order) {
    throw new ValidationError('Order is required');
  }

  if (!order.items || order.items.length === 0) {
    throw new ValidationError('Order must have at least one item');
  }

  if (order.total < 0) {
    throw new ValidationError('Order total cannot be negative');
  }

  // Safe property access
  const customerEmail = order.customer?.email ?? '[email protected]';

  // Proceed with valid data
  return {
    id: generateOrderId(),
    items: order.items.map(item => ({
      ...item,
      price: Math.max(0, item.price)  // Ensure non-negative
    })),
    total: order.total,
    customerEmail
  };
}

---

Naming Conventions

Functions

// Use verb + noun pattern
function getUser(id) { }           // Retrieval
function createOrder(data) { }     // Creation
function updateProfile(id, data) { } // Mutation
function deleteComment(id) { }     // Deletion
function validateEmail(email) { }  // Validation
function calculateTotal(items) { } // Calculation
function formatDate(date) { }      // Transformation
function isActive(user) { }        // Boolean check
function hasPermission(user, action) { } // Boolean check
function canEdit(user, resource) { }     // Boolean check

Variables

// Descriptive nouns
const userCount = 42;               // Not: n, count, uc
const activeUsers = users.filter(); // Not: arr, filtered
const maxRetryAttempts = 3;         // Not: max, retries

// Boolean variables
const isActive = true;              // is/has/can/should prefix
const hasPermission = false;
const canEdit = user.role === 'admin';
const shouldRetry = attempts < maxRetryAttempts;

// Collections are plural
const users = [];                   // Not: userList, userArray
const orderItems = [];              // Not: items (too generic)

// Maps/objects describe content
const userById = {};                // Not: userMap
const priceByProductId = {};        // Describes key-value relationship

Constants

// SCREAMING_SNAKE_CASE for true constants
const MAX_RETRY_ATTEMPTS = 3;
const DEFAULT_PAGE_SIZE = 20;
const API_BASE_URL = 'https://api.example.com';

// Configuration objects
const CONFIG = Object.freeze({
  database: {
    host: process.env.DB_HOST,
    port: parseInt(process.env.DB_PORT, 10)
  }
});

Classes

// PascalCase, noun-based
class UserRepository { }     // Not: UsersRepo, UserRepo
class OrderService { }       // Not: OrdersService
class EmailValidator { }     // Not: ValidateEmail
class PaymentGateway { }     // Not: PaymentGatewayService

// Interface names (TypeScript)
interface Cacheable { }      // Adjective for capabilities
interface UserRepository { } // Noun for contracts

---

Error Handling

Fail Fast, Recover Gracefully

async function createUser(data) {
  // Validate early
  if (!data.email) {
    throw new ValidationError('Email is required');
  }

  if (!isValidEmail(data.email)) {
    throw new ValidationError('Invalid email format');
  }

  // Check business rules
  const existing = await userRepo.findByEmail(data.email);
  if (existing) {
    throw new ConflictError('Email already registered');
  }

  // Proceed with operation
  try {
    const user = await userRepo.save(data);
    await emailService.sendWelcome(user.email);
    return user;
  } catch (error) {
    // Handle specific errors
    if (error instanceof DatabaseError) {
      logger.error('Database error creating user', { error, data });
      throw new ServiceError('Unable to create user, please try again');
    }
    throw error; // Re-throw unexpected errors
  }
}

Custom Error Classes

// Base application error
class AppError extends Error {
  constructor(message, code, statusCode = 500) {
    super(message);
    this.name = this.constructor.name;
    this.code = code;
    this.statusCode = statusCode;
    Error.captureStackTrace(this, this.constructor);
  }
}

// Specific error types
class ValidationError extends AppError {
  constructor(message, details = []) {
    super(message, 'VALIDATION_ERROR', 400);
    this.details = details;
  }
}

class NotFoundError extends AppError {
  constructor(resource, id) {
    super(`${resource} with id ${id} not found`, 'NOT_FOUND', 404);
    this.resource = resource;
    this.resourceId = id;
  }
}

class ConflictError extends AppError {
  constructor(message) {
    super(message, 'CONFLICT', 409);
  }
}

class UnauthorizedError extends AppError {
  constructor(message = 'Authentication required') {
    super(message, 'UNAUTHORIZED', 401);
  }
}

For comprehensive error patterns: See references/error-handling-patterns.md

---

Logging

Log Levels

Level	When to Use	Example
ERROR	Failures requiring attention	Database connection failed
WARN	Potentially harmful situations	Rate limit approaching
INFO	Normal operational events	User created, order placed
DEBUG	Detailed debugging info	Function parameters, intermediate values

Structured Logging

const logger = require('./logger');

// BAD: Unstructured logging
console.log('User created: ' + user.id);
console.log('Error: ' + error.message);

// GOOD: Structured logging
logger.info('User created', {
  userId: user.id,
  email: user.email,
  source: 'signup'
});

logger.error('Failed to process payment', {
  orderId: order.id,
  amount: order.total,
  error: error.message,
  errorCode: error.code,
  stack: error.stack
});

// Request logging middleware
app.use((req, res, next) => {
  const requestId = req.headers['x-request-id'] || uuidv4();
  req.requestId = requestId;

  logger.info('Request received', {
    requestId,
    method: req.method,
    path: req.path,
    userAgent: req.headers['user-agent'],
    ip: req.ip
  });

  res.on('finish', () => {
    logger.info('Request completed', {
      requestId,
      statusCode: res.statusCode,
      duration: Date.now() - req.startTime
    });
  });

  next();
});

---

Code Organization

File Size Guidelines

• Maximum file size: 500 lines
• Maximum function size: 50 lines
• Maximum line length: 100 characters

Module Structure

// 1. Imports (external first, then internal)
const express = require('express');
const { validate } = require('class-validator');

const { UserService } = require('../services/UserService');
const { logger } = require('../utils/logger');

// 2. Constants and configuration
const MAX_PAGE_SIZE = 100;
const DEFAULT_PAGE_SIZE = 20;

// 3. Main exports (class, function, or router)
class UserController {
  constructor(userService) {
    this.userService = userService;
  }

  async getUsers(req, res, next) {
    // Implementation
  }
}

// 4. Helper functions (private to module)
function validatePagination(page, limit) {
  // Implementation
}

// 5. Export statement
module.exports = { UserController };

---

Code Quality Checklist

Before completing CODE phase:

Structure

• Functions under 50 lines
• Files under 500 lines
• Single responsibility per function/class
• No deeply nested code (max 3 levels)

Naming

• Descriptive variable names
• Consistent naming conventions
• No abbreviations (except common ones: id, url, api)
• Boolean variables have is/has/can prefix

Error Handling

• All async operations have error handling
• Errors include relevant context
• No silent failures
• User-facing errors are friendly

Documentation

• Complex logic has comments
• Public APIs have JSDoc/docstrings
• No commented-out code
• No TODO comments without tickets

Quality

• No magic numbers (use named constants)
• No duplicate code
• Consistent code style
• Logging at appropriate levels

---

Scripts

Lint Check Script

A helper script is available at scripts/lint-check.sh to run project linters.

# From within the skill directory:
chmod +x scripts/lint-check.sh

# Run
./scripts/lint-check.sh

---

Detailed References

For comprehensive coding guidance:

• Clean Code Principles: references/clean-code-principles.md

  • SOLID principles in depth
  • Code smells and refactoring
  • Function design guidelines
  • Comment best practices

• Error Handling Patterns: references/error-handling-patterns.md

  • Error handling by language
  • Global error handlers
  • Retry strategies
  • Circuit breaker patterns