Modular Monolithic

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┌─────────────────────────────────────┐
│           API Gateway               │
├─────────────────────────────────────┤
│  ┌─────────┐  ┌─────────┐  ┌─────── │
│  │Product  │  │Order    │  │Payment │
│  │Module   │  │Module   │  │Module  │
│  └─────────┘  └─────────┘  └─────── │
│  ┌─────────┐  ┌─────────┐  ┌─────── │
│  │User     │  │Inventory│  │Shipping│
│  │Module   │  │Module   │  │Module  │
│  └─────────┘  └─────────┘  └─────── │
├─────────────────────────────────────┤
│           Event Bus                 │
├─────────────────────────────────────┤
│         Shared Kernel               │
└─────────────────────────────────────┘

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# 모듈러 모놀리틱 E-커머스 플랫폼 구현 예시

from abc import ABC, abstractmethod
from typing import Dict, List, Optional, Any
from dataclasses import dataclass, field
from datetime import datetime
from enum import Enum
import uuid
import asyncio
from collections import defaultdict

# =============================================================================
# 공유 커널 (Shared Kernel) - 공통 기능
# =============================================================================

class DomainEvent:
    """도메인 이벤트 기본 클래스"""
    def __init__(self, event_type: str, data: Dict[str, Any]):
        self.event_id = str(uuid.uuid4())
        self.event_type = event_type
        self.data = data
        self.timestamp = datetime.now()

class EventBus:
    """이벤트 버스 - 모듈 간 비동기 통신"""
    def __init__(self):
        self._subscribers: Dict[str, List[callable]] = defaultdict(list)
    
    def subscribe(self, event_type: str, handler: callable):
        """이벤트 구독"""
        self._subscribers[event_type].append(handler)
    
    async def publish(self, event: DomainEvent):
        """이벤트 발행"""
        handlers = self._subscribers.get(event.event_type, [])
        for handler in handlers:
            try:
                if asyncio.iscoroutinefunction(handler):
                    await handler(event)
                else:
                    handler(event)
            except Exception as e:
                print(f"Error handling event {event.event_type}: {e}")

class ModuleInterface(ABC):
    """모듈 인터페이스 - 모든 모듈이 구현해야 하는 기본 인터페이스"""
    
    @abstractmethod
    def get_name(self) -> str:
        pass
    
    @abstractmethod
    async def initialize(self, event_bus: EventBus):
        pass

# =============================================================================
# 상품 모듈 (Product Module)
# =============================================================================

@dataclass
class Product:
    """상품 엔티티"""
    id: str
    name: str
    description: str
    price: float
    category: str
    stock: int = 0
    created_at: datetime = field(default_factory=datetime.now)

class ProductRepository:
    """상품 리포지토리"""
    def __init__(self):
        self._products: Dict[str, Product] = {}
    
    def save(self, product: Product) -> Product:
        self._products[product.id] = product
        return product
    
    def find_by_id(self, product_id: str) -> Optional[Product]:
        return self._products.get(product_id)
    
    def find_all(self) -> List[Product]:
        return list(self._products.values())
    
    def find_by_category(self, category: str) -> List[Product]:
        return [p for p in self._products.values() if p.category == category]

class ProductService:
    """상품 도메인 서비스"""
    def __init__(self, repository: ProductRepository, event_bus: EventBus):
        self.repository = repository
        self.event_bus = event_bus
    
    async def create_product(self, name: str, description: str, price: float, 
                           category: str, stock: int) -> Product:
        """상품 생성"""
        product = Product(
            id=str(uuid.uuid4()),
            name=name,
            description=description,
            price=price,
            category=category,
            stock=stock
        )
        
        saved_product = self.repository.save(product)
        
        # 상품 생성 이벤트 발행
        event = DomainEvent("ProductCreated", {
            "product_id": saved_product.id,
            "name": saved_product.name,
            "price": saved_product.price,
            "stock": saved_product.stock
        })
        await self.event_bus.publish(event)
        
        return saved_product
    
    def get_product(self, product_id: str) -> Optional[Product]:
        """상품 조회"""
        return self.repository.find_by_id(product_id)
    
    def get_products_by_category(self, category: str) -> List[Product]:
        """카테고리별 상품 조회"""
        return self.repository.find_by_category(category)

class ProductModule(ModuleInterface):
    """상품 모듈"""
    def __init__(self):
        self.repository = ProductRepository()
        self.service = None
        self.event_bus = None
    
    def get_name(self) -> str:
        return "ProductModule"
    
    async def initialize(self, event_bus: EventBus):
        self.event_bus = event_bus
        self.service = ProductService(self.repository, event_bus)
        
        # 재고 업데이트 이벤트 구독
        event_bus.subscribe("StockUpdated", self._handle_stock_update)
    
    async def _handle_stock_update(self, event: DomainEvent):
        """재고 업데이트 이벤트 처리"""
        product_id = event.data.get("product_id")
        new_stock = event.data.get("new_stock")
        
        product = self.repository.find_by_id(product_id)
        if product:
            product.stock = new_stock
            self.repository.save(product)

# =============================================================================
# 주문 모듈 (Order Module)
# =============================================================================

class OrderStatus(Enum):
    PENDING = "pending"
    CONFIRMED = "confirmed"
    PROCESSING = "processing"
    SHIPPED = "shipped"
    DELIVERED = "delivered"
    CANCELLED = "cancelled"

@dataclass
class OrderItem:
    """주문 항목"""
    product_id: str
    product_name: str
    quantity: int
    unit_price: float
    
    @property
    def total_price(self) -> float:
        return self.quantity * self.unit_price

@dataclass
class Order:
    """주문 엔티티"""
    id: str
    customer_id: str
    items: List[OrderItem]
    status: OrderStatus = OrderStatus.PENDING
    created_at: datetime = field(default_factory=datetime.now)
    updated_at: datetime = field(default_factory=datetime.now)
    
    @property
    def total_amount(self) -> float:
        return sum(item.total_price for item in self.items)

class OrderRepository:
    """주문 리포지토리"""
    def __init__(self):
        self._orders: Dict[str, Order] = {}
    
    def save(self, order: Order) -> Order:
        order.updated_at = datetime.now()
        self._orders[order.id] = order
        return order
    
    def find_by_id(self, order_id: str) -> Optional[Order]:
        return self._orders.get(order_id)
    
    def find_by_customer(self, customer_id: str) -> List[Order]:
        return [o for o in self._orders.values() if o.customer_id == customer_id]

class OrderService:
    """주문 도메인 서비스"""
    def __init__(self, repository: OrderRepository, event_bus: EventBus):
        self.repository = repository
        self.event_bus = event_bus
    
    async def create_order(self, customer_id: str, items: List[Dict]) -> Order:
        """주문 생성"""
        order_items = []
        for item_data in items:
            order_item = OrderItem(
                product_id=item_data["product_id"],
                product_name=item_data["product_name"],
                quantity=item_data["quantity"],
                unit_price=item_data["unit_price"]
            )
            order_items.append(order_item)
        
        order = Order(
            id=str(uuid.uuid4()),
            customer_id=customer_id,
            items=order_items
        )
        
        saved_order = self.repository.save(order)
        
        # 주문 생성 이벤트 발행
        event = DomainEvent("OrderCreated", {
            "order_id": saved_order.id,
            "customer_id": saved_order.customer_id,
            "total_amount": saved_order.total_amount,
            "items": [{"product_id": item.product_id, "quantity": item.quantity} 
                     for item in saved_order.items]
        })
        await self.event_bus.publish(event)
        
        return saved_order
    
    async def update_order_status(self, order_id: str, status: OrderStatus):
        """주문 상태 업데이트"""
        order = self.repository.find_by_id(order_id)
        if order:
            old_status = order.status
            order.status = status
            self.repository.save(order)
            
            # 주문 상태 변경 이벤트 발행
            event = DomainEvent("OrderStatusChanged", {
                "order_id": order_id,
                "old_status": old_status.value,
                "new_status": status.value,
                "customer_id": order.customer_id
            })
            await self.event_bus.publish(event)

class OrderModule(ModuleInterface):
    """주문 모듈"""
    def __init__(self):
        self.repository = OrderRepository()
        self.service = None
        self.event_bus = None
    
    def get_name(self) -> str:
        return "OrderModule"
    
    async def initialize(self, event_bus: EventBus):
        self.event_bus = event_bus
        self.service = OrderService(self.repository, event_bus)
        
        # 결제 완료 이벤트 구독
        event_bus.subscribe("PaymentProcessed", self._handle_payment_processed)
    
    async def _handle_payment_processed(self, event: DomainEvent):
        """결제 완료 이벤트 처리"""
        order_id = event.data.get("order_id")
        if order_id:
            await self.service.update_order_status(order_id, OrderStatus.CONFIRMED)

# =============================================================================
# 결제 모듈 (Payment Module)
# =============================================================================

class PaymentStatus(Enum):
    PENDING = "pending"
    PROCESSING = "processing"
    SUCCESS = "success"
    FAILED = "failed"
    REFUNDED = "refunded"

@dataclass
class Payment:
    """결제 엔티티"""
    id: str
    order_id: str
    customer_id: str
    amount: float
    status: PaymentStatus = PaymentStatus.PENDING
    payment_method: str = "credit_card"
    created_at: datetime = field(default_factory=datetime.now)
    processed_at: Optional[datetime] = None

class PaymentRepository:
    """결제 리포지토리"""
    def __init__(self):
        self._payments: Dict[str, Payment] = {}
    
    def save(self, payment: Payment) -> Payment:
        self._payments[payment.id] = payment
        return payment
    
    def find_by_id(self, payment_id: str) -> Optional[Payment]:
        return self._payments.get(payment_id)
    
    def find_by_order_id(self, order_id: str) -> Optional[Payment]:
        for payment in self._payments.values():
            if payment.order_id == order_id:
                return payment
        return None

class PaymentService:
    """결제 도메인 서비스"""
    def __init__(self, repository: PaymentRepository, event_bus: EventBus):
        self.repository = repository
        self.event_bus = event_bus
    
    async def process_payment(self, order_id: str, customer_id: str, 
                            amount: float, payment_method: str = "credit_card") -> Payment:
        """결제 처리"""
        payment = Payment(
            id=str(uuid.uuid4()),
            order_id=order_id,
            customer_id=customer_id,
            amount=amount,
            payment_method=payment_method,
            status=PaymentStatus.PROCESSING
        )
        
        # 실제 결제 처리 로직 (외부 결제 게이트웨이 연동)
        # 여기서는 단순화하여 항상 성공으로 처리
        await asyncio.sleep(0.1)  # 결제 처리 시뮬레이션
        
        payment.status = PaymentStatus.SUCCESS
        payment.processed_at = datetime.now()
        
        saved_payment = self.repository.save(payment)
        
        # 결제 완료 이벤트 발행
        event = DomainEvent("PaymentProcessed", {
            "payment_id": saved_payment.id,
            "order_id": saved_payment.order_id,
            "customer_id": saved_payment.customer_id,
            "amount": saved_payment.amount,
            "status": saved_payment.status.value
        })
        await self.event_bus.publish(event)
        
        return saved_payment

class PaymentModule(ModuleInterface):
    """결제 모듈"""
    def __init__(self):
        self.repository = PaymentRepository()
        self.service = None
        self.event_bus = None
    
    def get_name(self) -> str:
        return "PaymentModule"
    
    async def initialize(self, event_bus: EventBus):
        self.event_bus = event_bus
        self.service = PaymentService(self.repository, event_bus)
        
        # 주문 생성 이벤트 구독
        event_bus.subscribe("OrderCreated", self._handle_order_created)
    
    async def _handle_order_created(self, event: DomainEvent):
        """주문 생성 이벤트 처리 - 자동 결제 처리"""
        order_id = event.data.get("order_id")
        customer_id = event.data.get("customer_id")
        total_amount = event.data.get("total_amount")
        
        if order_id and customer_id and total_amount:
            await self.service.process_payment(order_id, customer_id, total_amount)

# =============================================================================
# 애플리케이션 호스트 (Application Host)
# =============================================================================

class ECommerceApplication:
    """E-커머스 애플리케이션 호스트"""
    def __init__(self):
        self.event_bus = EventBus()
        self.modules: Dict[str, ModuleInterface] = {}
        
        # 모듈 등록
        self.register_module(ProductModule())
        self.register_module(OrderModule())
        self.register_module(PaymentModule())
    
    def register_module(self, module: ModuleInterface):
        """모듈 등록"""
        self.modules[module.get_name()] = module
    
    async def initialize(self):
        """애플리케이션 초기화"""
        print("🚀 E-커머스 모듈러 모놀리틱 애플리케이션 초기화 중…")
        
        for name, module in self.modules.items():
            await module.initialize(self.event_bus)
            print(f"✅ {name} 초기화 완료")
        
        print("🎉 애플리케이션 초기화 완료!")
    
    def get_module(self, module_name: str) -> Optional[ModuleInterface]:
        """모듈 조회"""
        return self.modules.get(module_name)

# =============================================================================
# 사용 예시 및 테스트
# =============================================================================

async def main():
    """애플리케이션 실행 예시"""
    app = ECommerceApplication()
    await app.initialize()
    
    # 모듈별 서비스 접근
    product_module = app.get_module("ProductModule")
    order_module = app.get_module("OrderModule")
    payment_module = app.get_module("PaymentModule")
    
    print("\n📦 상품 생성 예시:")
    # 상품 생성
    laptop = await product_module.service.create_product(
        name="Gaming Laptop",
        description="고성능 게이밍 노트북",
        price=1500000.0,
        category="Electronics",
        stock=10
    )
    print(f"생성된 상품: {laptop.name} - {laptop.price:,}원")
    
    mouse = await product_module.service.create_product(
        name="Gaming Mouse",
        description="게이밍 마우스",
        price=80000.0,
        category="Electronics",
        stock=50
    )
    print(f"생성된 상품: {mouse.name} - {mouse.price:,}원")
    
    print("\n🛒 주문 생성 예시:")
    # 주문 생성
    order = await order_module.service.create_order(
        customer_id="customer_123",
        items=[
            {
                "product_id": laptop.id,
                "product_name": laptop.name,
                "quantity": 1,
                "unit_price": laptop.price
            },
            {
                "product_id": mouse.id,
                "product_name": mouse.name,
                "quantity": 2,
                "unit_price": mouse.price
            }
        ]
    )
    print(f"생성된 주문 ID: {order.id}")
    print(f"주문 총액: {order.total_amount:,}원")
    print(f"주문 상태: {order.status.value}")
    
    # 잠시 대기 (이벤트 처리 시간)
    await asyncio.sleep(0.2)
    
    # 결제 확인
    payment = payment_module.repository.find_by_order_id(order.id)
    if payment:
        print(f"\n💳 결제 처리 완료:")
        print(f"결제 ID: {payment.id}")
        print(f"결제 상태: {payment.status.value}")
        print(f"결제 금액: {payment.amount:,}원")
    
    # 주문 상태 확인
    updated_order = order_module.repository.find_by_id(order.id)
    print(f"\n📋 최종 주문 상태: {updated_order.status.value}")

if __name__ == "__main__":
    asyncio.run(main())

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# 모듈별로 클래스로 분리 (간단 예시)
class OrderModule:
    def create_order(self, item_id, user_id):
        # 결제 모듈 호출
        payment_result = PaymentModule().process_payment(user_id, 10000)
        if payment_result:
            # 재고 모듈 호출
            inventory_result = InventoryModule().check_stock(item_id)
            if inventory_result:
                return "Order created"
        return "Order failed"

class PaymentModule:
    def process_payment(self, user_id, amount):
        return True  # 결제 성공 가정

class InventoryModule:
    def check_stock(self, item_id):
        return True  # 재고 있음 가정

# 사용 예시
order = OrderModule()
print(order.create_order("item1", "user1"))

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// 모듈러 모놀리스 구현 예시 (Node.js/TypeScript)

// 1. 도메인 이벤트 정의
interface DomainEvent {
  eventId: string;
  eventType: string;
  aggregateId: string;
  payload: any;
  occurredAt: Date;
}

// 2. Event Bus 구현 (모듈 간 통신)
class EventBus {
  private handlers: Map<string, Array<(event: DomainEvent) => Promise<void>>> = new Map();

  // 이벤트 핸들러 등록
  subscribe(eventType: string, handler: (event: DomainEvent) => Promise<void>): void {
    if (!this.handlers.has(eventType)) {
      this.handlers.set(eventType, []);
    }
    this.handlers.get(eventType)!.push(handler);
  }

  // 이벤트 발행 (비동기 처리)
  async publish(event: DomainEvent): Promise<void> {
    const handlers = this.handlers.get(event.eventType) || [];
    
    // Outbox 패턴 구현: 이벤트를 먼저 데이터베이스에 저장
    await this.saveToOutbox(event);
    
    // 핸들러들을 비동기로 실행
    await Promise.all(handlers.map(handler => 
      handler(event).catch(error => 
        console.error(`Event handler failed for ${event.eventType}:`, error)
      )
    ));
  }

  // Outbox 패턴: 이벤트를 데이터베이스에 먼저 저장
  private async saveToOutbox(event: DomainEvent): Promise<void> {
    // 실제 구현에서는 데이터베이스에 저장
    console.log(`Saving event to outbox: ${event.eventType}`);
  }
}

// 3. 주문 모듈 (Orders Module) 구현
namespace OrdersModule {
  
  // 주문 집계 루트
  export class Order {
    constructor(
      public readonly id: string,
      public readonly customerId: string,
      public readonly items: OrderItem[],
      public status: OrderStatus = OrderStatus.Pending
    ) {}

    // 주문 확인 비즈니스 로직
    confirm(): DomainEvent {
      if (this.status !== OrderStatus.Pending) {
        throw new Error('Only pending orders can be confirmed');
      }
      
      this.status = OrderStatus.Confirmed;
      
      return {
        eventId: crypto.randomUUID(),
        eventType: 'OrderConfirmed',
        aggregateId: this.id,
        payload: {
          orderId: this.id,
          customerId: this.customerId,
          items: this.items,
          totalAmount: this.calculateTotal()
        },
        occurredAt: new Date()
      };
    }

    private calculateTotal(): number {
      return this.items.reduce((sum, item) => sum + (item.price * item.quantity), 0);
    }
  }

  export interface OrderItem {
    productId: string;
    quantity: number;
    price: number;
  }

  export enum OrderStatus {
    Pending = 'pending',
    Confirmed = 'confirmed',
    Shipped = 'shipped',
    Delivered = 'delivered'
  }

  // 주문 모듈의 공개 API
  export class OrdersAPI {
    constructor(
      private eventBus: EventBus,
      private orderRepository: OrderRepository
    ) {}

    // 주문 생성 API
    async createOrder(customerId: string, items: OrderItem[]): Promise<string> {
      const orderId = crypto.randomUUID();
      const order = new Order(orderId, customerId, items);
      
      await this.orderRepository.save(order);
      
      const event: DomainEvent = {
        eventId: crypto.randomUUID(),
        eventType: 'OrderCreated',
        aggregateId: orderId,
        payload: { orderId, customerId, items },
        occurredAt: new Date()
      };
      
      await this.eventBus.publish(event);
      return orderId;
    }

    // 주문 확인 API
    async confirmOrder(orderId: string): Promise<void> {
      const order = await this.orderRepository.findById(orderId);
      if (!order) {
        throw new Error('Order not found');
      }

      const event = order.confirm();
      await this.orderRepository.save(order);
      await this.eventBus.publish(event);
    }
  }

  // 리포지토리 인터페이스 (데이터 액세스 추상화)
  export interface OrderRepository {
    save(order: Order): Promise<void>;
    findById(id: string): Promise<Order | null>;
  }
}

// 4. 재고 모듈 (Inventory Module) 구현
namespace InventoryModule {
  
  export class InventoryItem {
    constructor(
      public readonly productId: string,
      public availableQuantity: number,
      public reservedQuantity: number = 0
    ) {}

    // 재고 예약 비즈니스 로직
    reserve(quantity: number): void {
      if (this.availableQuantity < quantity) {
        throw new Error('Insufficient inventory');
      }
      
      this.availableQuantity -= quantity;
      this.reservedQuantity += quantity;
    }
  }

  // 재고 모듈의 공개 API
  export class InventoryAPI {
    constructor(
      private eventBus: EventBus,
      private inventoryRepository: InventoryRepository
    ) {
      // 주문 생성 이벤트 구독
      this.eventBus.subscribe('OrderCreated', this.handleOrderCreated.bind(this));
    }

    // 주문 생성 이벤트 핸들러 (모듈 간 통신)
    private async handleOrderCreated(event: DomainEvent): Promise<void> {
      const { orderId, items } = event.payload;
      
      console.log(`Processing inventory reservation for order: ${orderId}`);
      
      try {
        // 모든 아이템에 대해 재고 예약
        for (const item of items) {
          await this.reserveInventory(item.productId, item.quantity);
        }
        
        // 재고 예약 완료 이벤트 발행
        const reservedEvent: DomainEvent = {
          eventId: crypto.randomUUID(),
          eventType: 'InventoryReserved',
          aggregateId: orderId,
          payload: { orderId, items },
          occurredAt: new Date()
        };
        
        await this.eventBus.publish(reservedEvent);
        
      } catch (error) {
        // 재고 부족 시 보상 이벤트 발행
        const failedEvent: DomainEvent = {
          eventId: crypto.randomUUID(),
          eventType: 'InventoryReservationFailed',
          aggregateId: orderId,
          payload: { orderId, error: error.message },
          occurredAt: new Date()
        };
        
        await this.eventBus.publish(failedEvent);
      }
    }

    // 재고 예약 API
    async reserveInventory(productId: string, quantity: number): Promise<void> {
      const inventory = await this.inventoryRepository.findByProductId(productId);
      if (!inventory) {
        throw new Error(`Product ${productId} not found in inventory`);
      }
      
      inventory.reserve(quantity);
      await this.inventoryRepository.save(inventory);
    }
  }

  export interface InventoryRepository {
    save(inventory: InventoryItem): Promise<void>;
    findByProductId(productId: string): Promise<InventoryItem | null>;
  }
}

// 5. 애플리케이션 부트스트랩 (모든 모듈 조합)
class ModularMonolithApp {
  private eventBus: EventBus;
  private ordersAPI: OrdersModule.OrdersAPI;
  private inventoryAPI: InventoryModule.InventoryAPI;

  constructor() {
    this.eventBus = new EventBus();
    
    // 각 모듈 초기화 (의존성 주입)
    this.ordersAPI = new OrdersModule.OrdersAPI(
      this.eventBus,
      new MockOrderRepository() // 실제 구현에서는 실제 리포지토리 사용
    );
    
    this.inventoryAPI = new InventoryModule.InventoryAPI(
      this.eventBus,
      new MockInventoryRepository() // 실제 구현에서는 실제 리포지토리 사용
    );
  }

  // 애플리케이션 시작
  async start(): Promise<void> {
    console.log('Modular Monolith Application started');
    
    // 예시: 주문 생성 플로우
    try {
      const orderId = await this.ordersAPI.createOrder('customer-123', [
        { productId: 'product-1', quantity: 2, price: 10.00 },
        { productId: 'product-2', quantity: 1, price: 25.00 }
      ]);
      
      console.log(`Order created: ${orderId}`);
      
      // 잠시 후 주문 확인
      setTimeout(async () => {
        await this.ordersAPI.confirmOrder(orderId);
        console.log(`Order confirmed: ${orderId}`);
      }, 1000);
      
    } catch (error) {
      console.error('Order processing failed:', error);
    }
  }
}

// 6. Mock Repositories (실제 구현에서는 실제 데이터베이스 연동)
class MockOrderRepository implements OrdersModule.OrderRepository {
  private orders = new Map<string, OrdersModule.Order>();

  async save(order: OrdersModule.Order): Promise<void> {
    this.orders.set(order.id, order);
  }

  async findById(id: string): Promise<OrdersModule.Order | null> {
    return this.orders.get(id) || null;
  }
}

class MockInventoryRepository implements InventoryModule.InventoryRepository {
  private inventory = new Map<string, InventoryModule.InventoryItem>([
    ['product-1', new InventoryModule.InventoryItem('product-1', 100)],
    ['product-2', new InventoryModule.InventoryItem('product-2', 50)]
  ]);

  async save(inventory: InventoryModule.InventoryItem): Promise<void> {
    this.inventory.set(inventory.productId, inventory);
  }

  async findByProductId(productId: string): Promise<InventoryModule.InventoryItem | null> {
    return this.inventory.get(productId) || null;
  }
}

// 애플리케이션 실행
const app = new ModularMonolithApp();
app.start();