Backend Architect

# System Architecture Specification

## High-Level Architecture
**Architecture Pattern**: Microservices with event-driven communication
**Communication Pattern**: REST for synchronous, Event bus for async
**Data Pattern**: CQRS with Event Sourcing for complex domains
**Deployment Pattern**: Container orchestration with Kubernetes

## Service Decomposition
### Core Services
**User Service**: Authentication, user management, profiles
- Database: PostgreSQL with user data encryption
- APIs: REST endpoints for user operations
- Events: User created, updated, deleted events

**Product Service**: Product catalog, inventory management
- Database: PostgreSQL with read replicas
- Cache: Redis for frequently accessed products
- APIs: GraphQL for flexible product queries

**Order Service**: Order processing, payment integration
- Database: PostgreSQL with ACID compliance
- Queue: RabbitMQ for order processing pipeline
- APIs: REST with webhook callbacks

-- E-commerce Database Schema Design

-- Users table with proper indexing and security
CREATE TABLE users (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    email VARCHAR(255) UNIQUE NOT NULL,
    password_hash VARCHAR(255) NOT NULL, -- bcrypt hashed
    first_name VARCHAR(100) NOT NULL,
    last_name VARCHAR(100) NOT NULL,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
    deleted_at TIMESTAMP WITH TIME ZONE NULL -- Soft delete
);

-- Indexes for performance
CREATE INDEX idx_users_email ON users(email) WHERE deleted_at IS NULL;
CREATE INDEX idx_users_created_at ON users(created_at);

-- Products table with proper normalization
CREATE TABLE products (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name VARCHAR(255) NOT NULL,
    description TEXT,
    price DECIMAL(10,2) NOT NULL CHECK (price >= 0),
    category_id UUID REFERENCES categories(id),
    inventory_count INTEGER DEFAULT 0 CHECK (inventory_count >= 0),
    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
    updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
    is_active BOOLEAN DEFAULT true
);

-- Optimized indexes for common queries
CREATE INDEX idx_products_category ON products(category_id) WHERE is_active = true;
CREATE INDEX idx_products_price ON products(price) WHERE is_active = true;
CREATE INDEX idx_products_name_search ON products USING gin(to_tsvector('english', name));

// Express.js API Architecture with proper error handling

const express = require('express');
const helmet = require('helmet');
const rateLimit = require('express-rate-limit');
const { authenticate, authorize } = require('./middleware/auth');

const app = express();

// Security middleware
app.use(helmet({
  contentSecurityPolicy: {
    directives: {
      defaultSrc: ["'self'"],
      styleSrc: ["'self'", "'unsafe-inline'"],
      scriptSrc: ["'self'"],
      imgSrc: ["'self'", "data:", "https:"],
    },
  },
}));

// Rate limiting
const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // limit each IP to 100 requests per windowMs
  message: 'Too many requests from this IP, please try again later.',
  standardHeaders: true,
  legacyHeaders: false,
});
app.use('/api', limiter);

// API Routes with proper validation and error handling
app.get('/api/users/:id', 
  authenticate,
  async (req, res, next) => {
    try {
      const user = await userService.findById(req.params.id);
      if (!user) {
        return res.status(404).json({
          error: 'User not found',
          code: 'USER_NOT_FOUND'
        });
      }
      
      res.json({
        data: user,
        meta: { timestamp: new Date().toISOString() }
      });
    } catch (error) {
      next(error);
    }
  }
);