Exemples Event Sourcing

// Event Store Implementation
interface Event {
  id: string
  aggregateId: string
  type: string
  data: any
  timestamp: Date
  version: number
}

class EventStore {
  private events: Map<string, Event[]> = new Map()

  async saveEvents(aggregateId: string, events: Event[]): Promise<void> {
    const existingEvents = this.events.get(aggregateId) || []
    const newEvents = events.map((event, index) => ({
      ...event,
      id: crypto.randomUUID(),
      timestamp: new Date(),
      version: existingEvents.length + index + 1
    }))

    this.events.set(aggregateId, [...existingEvents, ...newEvents])
  }

  async getEvents(aggregateId: string): Promise<Event[]> {
    return this.events.get(aggregateId) || []
  }

  async getEventsFromVersion(aggregateId: string, fromVersion: number): Promise<Event[]> {
    const events = this.events.get(aggregateId) || []
    return events.filter(event => event.version >= fromVersion)
  }
}

// Aggregate Root
abstract class AggregateRoot {
  private _id: string
  private _version: number = 0
  private _uncommittedEvents: Event[] = []

  constructor(id: string) {
    this._id = id
  }

  get id(): string {
    return this._id
  }

  get version(): number {
    return this._version
  }

  protected apply(event: Event): void {
    this.applyChange(event, true)
    this._uncommittedEvents.push(event)
  }

  private applyChange(event: Event, isNew: boolean): void {
    const handler = this.getEventHandler(event.type)
    if (handler) {
      handler.call(this, event.data)
    }

    if (isNew) {
      this._version = event.version
    }
  }

  protected abstract getEventHandler(eventType: string): Function | null

  async markChangesAsCommitted(): Promise<void> {
    this._uncommittedEvents = []
  }

  getUncommittedEvents(): Event[] {
    return [...this._uncommittedEvents]
  }

  async loadFromHistory(events: Event[]): Promise<void> {
    for (const event of events) {
      this.applyChange(event, false)
      this._version = event.version
    }
  }
}

// Shopping Cart Example
interface CartItem {
  productId: string
  productName: string
  quantity: number
  unitPrice: number
}

interface CartEventData {
  productId?: string
  productName?: string
  quantity?: number
  unitPrice?: number
  items?: CartItem[]
}

class ShoppingCart extends AggregateRoot {
  private items: CartItem[] = []
  private isActive: boolean = true

  constructor(id: string) {
    super(id)
  }

  addItem(productId: string, productName: string, quantity: number, unitPrice: number): void {
    if (!this.isActive) {
      throw new Error('Cannot add items to inactive cart')
    }

    const event: Event = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'ITEM_ADDED',
      data: { productId, productName, quantity, unitPrice },
      timestamp: new Date(),
      version: this.version + 1
    }

    this.apply(event)
  }

  removeItem(productId: string): void {
    const item = this.items.find(item => item.productId === productId)
    if (!item) {
      throw new Error('Item not found in cart')
    }

    const event: Event = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'ITEM_REMOVED',
      data: { productId },
      timestamp: new Date(),
      version: this.version + 1
    }

    this.apply(event)
  }

  checkout(): void {
    if (this.items.length === 0) {
      throw new Error('Cannot checkout empty cart')
    }

    const event: Event = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'CART_CHECKED_OUT',
      data: { items: [...this.items] },
      timestamp: new Date(),
      version: this.version + 1
    }

    this.apply(event)
  }

  protected getEventHandler(eventType: string): Function | null {
    const handlers: Record<string, Function> = {
      'ITEM_ADDED': this.handleItemAdded.bind(this),
      'ITEM_REMOVED': this.handleItemRemoved.bind(this),
      'CART_CHECKED_OUT': this.handleCartCheckedOut.bind(this)
    }
    return handlers[eventType] || null
  }

  private handleItemAdded(data: CartEventData): void {
    const existingItem = this.items.find(item => item.productId === data.productId)

    if (existingItem) {
      existingItem.quantity += data.quantity!
    } else {
      this.items.push({
        productId: data.productId!,
        productName: data.productName!,
        quantity: data.quantity!,
        unitPrice: data.unitPrice!
      })
    }
  }

  private handleItemRemoved(data: CartEventData): void {
    this.items = this.items.filter(item => item.productId !== data.productId)
  }

  private handleCartCheckedOut(): void {
    this.isActive = false
  }

  getItems(): CartItem[] {
    return [...this.items]
  }

  getTotalPrice(): number {
    return this.items.reduce((total, item) => total + (item.quantity * item.unitPrice), 0)
  }

  isCartActive(): boolean {
    return this.isActive
  }
}

// Usage Example
async function example() {
  const eventStore = new EventStore()
  const cart = new ShoppingCart('cart-123')

  // Add items to cart
  cart.addItem('prod-1', 'Laptop', 1, 999.99)
  cart.addItem('prod-2', 'Mouse', 2, 29.99)

  // Save uncommitted events
  await eventStore.saveEvents(cart.id, cart.getUncommittedEvents())
  await cart.markChangesAsCommitted()

  console.log('Cart items:', cart.getItems())
  console.log('Total price:', cart.getTotalPrice())

  // Checkout
  cart.checkout()
  await eventStore.saveEvents(cart.id, cart.getUncommittedEvents())
  await cart.markChangesAsCommitted()

  console.log('Cart is active:', cart.isCartActive())
}

export { Event, EventStore, AggregateRoot, ShoppingCart, example }
        

// CQRS Base Classes
interface Command {
  id: string
  aggregateId: string
  timestamp: Date
}

interface Query {
  id: string
  parameters: Record<string, any>
}

interface CommandResult {
  success: boolean
  message?: string
  data?: any
}

interface QueryResult<T = any> {
  success: boolean
  data?: T
  error?: string
}

// Command Handler Interface
interface ICommandHandler<T extends Command> {
  handle(command: T): Promise<CommandResult>
}

// Query Handler Interface
interface IQueryHandler<T extends Query, R> {
  handle(query: T): Promise<QueryResult<R>>
}

// Command Bus
class CommandBus {
  private handlers: Map<string, ICommandHandler<any>> = new Map()

  register<T extends Command>(commandType: string, handler: ICommandHandler<T>): void {
    this.handlers.set(commandType, handler)
  }

  async dispatch<T extends Command>(command: T): Promise<CommandResult> {
    const handler = this.handlers.get(command.constructor.name)
    if (!handler) {
      return {
        success: false,
        message: `No handler found for command: ${command.constructor.name}`
      }
    }

    try {
      return await handler.handle(command)
    } catch (error) {
      return {
        success: false,
        message: error instanceof Error ? error.message : 'Unknown error'
      }
    }
  }
}

// Query Bus
class QueryBus {
  private handlers: Map<string, IQueryHandler<any, any>> = new Map()

  register<T extends Query, R>(queryType: string, handler: IQueryHandler<T, R>): void {
    this.handlers.set(queryType, handler)
  }

  async dispatch<T extends Query, R>(query: T): Promise<QueryResult<R>> {
    const handler = this.handlers.get(query.constructor.name)
    if (!handler) {
      return {
        success: false,
        error: `No handler found for query: ${query.constructor.name}`
      }
    }

    try {
      return await handler.handle(query)
    } catch (error) {
      return {
        success: false,
        error: error instanceof Error ? error.message : 'Unknown error'
      }
    }
  }
}

// Domain Events
interface DomainEvent {
  id: string
  aggregateId: string
  type: string
  data: any
  timestamp: Date
  version: number
}

// Event Publisher
interface EventPublisher {
  publish(events: DomainEvent[]): Promise<void>
}

// Console Event Publisher (for demo)
class ConsoleEventPublisher implements EventPublisher {
  async publish(events: DomainEvent[]): Promise<void> {
    console.log('Publishing events:', events.length)
    for (const event of events) {
      console.log(`Event: ${event.type}, Aggregate: ${event.aggregateId}`)
    }
  }
}

// Order Management Commands
class CreateOrderCommand implements Command {
  id: string
  aggregateId: string
  timestamp: Date

  constructor(
    public customerId: string,
    public items: OrderItem[]
  ) {
    this.id = crypto.randomUUID()
    this.aggregateId = crypto.randomUUID()
    this.timestamp = new Date()
  }
}

class UpdateOrderCommand implements Command {
  id: string
  aggregateId: string
  timestamp: Date

  constructor(
    public orderId: string,
    public items: OrderItem[]
  ) {
    this.id = crypto.randomUUID()
    this.aggregateId = orderId
    this.timestamp = new Date()
  }
}

class CancelOrderCommand implements Command {
  id: string
  aggregateId: string
  timestamp: Date

  constructor(
    public orderId: string,
    public reason: string
  ) {
    this.id = crypto.randomUUID()
    this.aggregateId = orderId
    this.timestamp = new Date()
  }
}

// Order Management Queries
class GetOrderByIdQuery implements Query {
  id: string
  parameters: Record<string, any>

  constructor(public orderId: string) {
    this.id = crypto.randomUUID()
    this.parameters = { orderId }
  }
}

class GetOrdersByCustomerQuery implements Query {
  id: string
  parameters: Record<string, any>

  constructor(public customerId: string) {
    this.id = crypto.randomUUID()
    this.parameters = { customerId }
  }
}

interface OrderItem {
  productId: string
  productName: string
  quantity: number
  unitPrice: number
}

// Write Model - Order Aggregate
class Order {
  private events: DomainEvent[] = []

  constructor(
    public readonly id: string,
    public readonly customerId: string,
    public items: OrderItem[],
    public status: 'PENDING' | 'CONFIRMED' | 'CANCELLED' | 'COMPLETED' = 'PENDING',
    public createdAt: Date = new Date(),
    public updatedAt: Date = new Date()
  ) {}

  updateItems(newItems: OrderItem[]): void {
    if (this.status !== 'PENDING') {
      throw new Error('Cannot update order in current status')
    }

    const event: DomainEvent = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'ORDER_ITEMS_UPDATED',
      data: { oldItems: this.items, newItems },
      timestamp: new Date(),
      version: 1
    }

    this.items = newItems
    this.updatedAt = new Date()
    this.events.push(event)
  }

  cancel(reason: string): void {
    if (this.status === 'COMPLETED') {
      throw new Error('Cannot complete order')
    }

    const event: DomainEvent = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'ORDER_CANCELLED',
      data: { reason },
      timestamp: new Date(),
      version: 1
    }

    this.status = 'CANCELLED'
    this.updatedAt = new Date()
    this.events.push(event)
  }

  confirm(): void {
    if (this.status !== 'PENDING') {
      throw new Error('Order must be in PENDING status to be confirmed')
    }

    const event: DomainEvent = {
      id: crypto.randomUUID(),
      aggregateId: this.id,
      type: 'ORDER_CONFIRMED',
      data: { confirmedAt: new Date() },
      timestamp: new Date(),
      version: 1
    }

    this.status = 'CONFIRMED'
    this.updatedAt = new Date()
    this.events.push(event)
  }

  getUncommittedEvents(): DomainEvent[] {
    return [...this.events]
  }

  markEventsAsCommitted(): void {
    this.events = []
  }
}

// Read Model - Order Summary
interface OrderSummary {
  id: string
  customerId: string
  itemCount: number
  totalAmount: number
  status: string
  createdAt: Date
  updatedAt: Date
}

// Read Model Repository
class OrderReadRepository {
  private orders: Map<string, OrderSummary> = new Map()

  async save(orderSummary: OrderSummary): Promise<void> {
    this.orders.set(orderSummary.id, orderSummary)
  }

  async findById(orderId: string): Promise<OrderSummary | null> {
    return this.orders.get(orderId) || null
  }

  async findByCustomerId(customerId: string): Promise<OrderSummary[]> {
    return Array.from(this.orders.values()).filter(order => order.customerId === customerId)
  }
}

// Write Model Repository
class OrderWriteRepository {
  private orders: Map<string, Order> = new Map()

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

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

// Command Handlers
class CreateOrderHandler implements ICommandHandler<CreateOrderCommand> {
  constructor(
    private orderRepository: OrderWriteRepository,
    private readRepository: OrderReadRepository,
    private eventPublisher: EventPublisher
  ) {}

  async handle(command: CreateOrderCommand): Promise<CommandResult> {
    const order = new Order(command.aggregateId, command.customerId, command.items)

    await this.orderRepository.save(order)

    // Create read model
    const orderSummary: OrderSummary = {
      id: order.id,
      customerId: order.customerId,
      itemCount: order.items.length,
      totalAmount: order.items.reduce((sum, item) => sum + (item.quantity * item.unitPrice), 0),
      status: order.status,
      createdAt: order.createdAt,
      updatedAt: order.updatedAt
    }

    await this.readRepository.save(orderSummary)

    // Publish events
    await this.eventPublisher.publish(order.getUncommittedEvents())
    order.markEventsAsCommitted()

    return {
      success: true,
      message: 'Order created successfully',
      data: { orderId: order.id }
    }
  }
}

class CancelOrderHandler implements ICommandHandler<CancelOrderCommand> {
  constructor(
    private orderRepository: OrderWriteRepository,
    private readRepository: OrderReadRepository,
    private eventPublisher: EventPublisher
  ) {}

  async handle(command: CancelOrderCommand): Promise<CommandResult> {
    const order = await this.orderRepository.findById(command.orderId)
    if (!order) {
      return {
        success: false,
        message: 'Order not found'
      }
    }

    try {
      order.cancel(command.reason)
      await this.orderRepository.save(order)

      // Update read model
      const orderSummary = await this.readRepository.findById(command.orderId)
      if (orderSummary) {
        orderSummary.status = order.status
        orderSummary.updatedAt = order.updatedAt
        await this.readRepository.save(orderSummary)
      }

      // Publish events
      await this.eventPublisher.publish(order.getUncommittedEvents())
      order.markEventsAsCommitted()

      return {
        success: true,
        message: 'Order cancelled successfully'
      }
    } catch (error) {
      return {
        success: false,
        message: error instanceof Error ? error.message : 'Failed to cancel order'
      }
    }
  }
}

// Query Handlers
class GetOrderByIdHandler implements IQueryHandler<GetOrderByIdQuery, OrderSummary | null> {
  constructor(private readRepository: OrderReadRepository) {}

  async handle(query: GetOrderByIdQuery): Promise<QueryResult<OrderSummary | null>> {
    try {
      const order = await this.readRepository.findById(query.orderId)
      return {
        success: true,
        data: order
      }
    } catch (error) {
      return {
        success: false,
        error: error instanceof Error ? error.message : 'Failed to get order'
      }
    }
  }
}

class GetOrdersByCustomerHandler implements IQueryHandler<GetOrdersByCustomerQuery, OrderSummary[]> {
  constructor(private readRepository: OrderReadRepository) {}

  async handle(query: GetOrdersByCustomerQuery): Promise<QueryResult<OrderSummary[]>> {
    try {
      const orders = await this.readRepository.findByCustomerId(query.customerId)
      return {
        success: true,
        data: orders
      }
    } catch (error) {
      return {
        success: false,
        error: error instanceof Error ? error.message : 'Failed to get orders'
      }
    }
  }
}

// Application Setup and Usage
async function setupApplication() {
  const commandBus = new CommandBus()
  const queryBus = new QueryBus()

  const orderWriteRepo = new OrderWriteRepository()
  const orderReadRepo = new OrderReadRepository()
  const eventPublisher = new ConsoleEventPublisher()

  // Register command handlers
  commandBus.register('CreateOrderCommand', new CreateOrderHandler(orderWriteRepo, orderReadRepo, eventPublisher))
  commandBus.register('CancelOrderCommand', new CancelOrderHandler(orderWriteRepo, orderReadRepo, eventPublisher))

  // Register query handlers
  queryBus.register('GetOrderByIdQuery', new GetOrderByIdHandler(orderReadRepo))
  queryBus.register('GetOrdersByCustomerQuery', new GetOrdersByCustomerHandler(orderReadRepo))

  return { commandBus, queryBus }
}

// Usage Example
async function cqrsExample() {
  const { commandBus, queryBus } = await setupApplication()

  // Create order
  const createOrderCommand = new CreateOrderCommand('customer-123', [
    { productId: 'prod-1', productName: 'Laptop', quantity: 1, unitPrice: 999.99 },
    { productId: 'prod-2', productName: 'Mouse', quantity: 2, unitPrice: 29.99 }
  ])

  const createResult = await commandBus.dispatch(createOrderCommand)
  console.log('Create order result:', createResult)

  if (createResult.success) {
    const orderId = createResult.data.orderId

    // Query order by ID
    const getOrderQuery = new GetOrderByIdQuery(orderId)
    const orderResult = await queryBus.dispatch(getOrderQuery)
    console.log('Order details:', orderResult.data)

    // Query orders by customer
    const getCustomerOrdersQuery = new GetOrdersByCustomerQuery('customer-123')
    const customerOrdersResult = await queryBus.dispatch(getCustomerOrdersQuery)
    console.log('Customer orders:', customerOrdersResult.data)

    // Cancel order
    const cancelOrderCommand = new CancelOrderCommand(orderId, 'Customer requested cancellation')
    const cancelResult = await commandBus.dispatch(cancelOrderCommand)
    console.log('Cancel order result:', cancelResult)
  }
}

export {
  Command,
  Query,
  CommandBus,
  QueryBus,
  CommandResult,
  QueryResult,
  CreateOrderCommand,
  CancelOrderCommand,
  GetOrderByIdQuery,
  GetOrdersByCustomerQuery,
  cqrsExample
}
        

// State Reconstruction Engine
interface Event {
  id: string
  aggregateId: string
  type: string
  data: any
  timestamp: Date
  version: number
}

interface Snapshot {
  aggregateId: string
  data: any
  version: number
  timestamp: Date
}

interface StateReconstructor<T> {
  reconstruct(events: Event[]): T
  createSnapshot(state: T, version: number): Snapshot
  applySnapshot(snapshot: Snapshot, events: Event[]): T
}

// Snapshot Strategy
interface SnapshotStrategy {
  shouldTakeSnapshot(aggregateId: string, version: number): boolean
  getSnapshotInterval(): number
}

class IntervalSnapshotStrategy implements SnapshotStrategy {
  constructor(private interval: number = 100) {}

  shouldTakeSnapshot(aggregateId: string, version: number): boolean {
    return version % this.interval === 0
  }

  getSnapshotInterval(): number {
    return this.interval
  }
}

class EventCountSnapshotStrategy implements SnapshotStrategy {
  constructor(private eventCountThreshold: number = 50) {}

  shouldTakeSnapshot(aggregateId: string, version: number): boolean {
    // This would need to track event count since last snapshot
    return version % this.eventCountThreshold === 0
  }

  getSnapshotInterval(): number {
    return this.eventCountThreshold
  }
}

// Snapshot Store
class SnapshotStore {
  private snapshots: Map<string, Snapshot[]> = new Map()

  async saveSnapshot(snapshot: Snapshot): Promise<void> {
    const aggregateSnapshots = this.snapshots.get(snapshot.aggregateId) || []

    // Remove older snapshots to save space (keep only the latest)
    const filteredSnapshots = aggregateSnapshots.filter(s => s.version < snapshot.version)
    filteredSnapshots.push(snapshot)

    this.snapshots.set(snapshot.aggregateId, filteredSnapshots)
  }

  async getLatestSnapshot(aggregateId: string): Promise<Snapshot | null> {
    const aggregateSnapshots = this.snapshots.get(aggregateId) || []
    if (aggregateSnapshots.length === 0) {
      return null
    }

    return aggregateSnapshots.reduce((latest, current) =>
      current.version > latest.version ? current : latest
    )
  }

  async getSnapshotBeforeVersion(aggregateId: string, version: number): Promise<Snapshot | null> {
    const aggregateSnapshots = this.snapshots.get(aggregateId) || []
    const matchingSnapshots = aggregateSnapshots.filter(s => s.version <= version)

    if (matchingSnapshots.length === 0) {
      return null
    }

    return matchingSnapshots.reduce((latest, current) =>
      current.version > latest.version ? current : latest
    )
  }

  async deleteSnapshotsBeforeVersion(aggregateId: string, version: number): Promise<void> {
    const aggregateSnapshots = this.snapshots.get(aggregateId) || []
    const filteredSnapshots = aggregateSnapshots.filter(s => s.version >= version)
    this.snapshots.set(aggregateId, filteredSnapshots)
  }
}

// Event Store with Snapshot Integration
class EnhancedEventStore {
  constructor(
    private events: Map<string, Event[]> = new Map(),
    private snapshotStore: SnapshotStore = new SnapshotStore(),
    private snapshotStrategy: SnapshotStrategy = new IntervalSnapshotStrategy(100)
  ) {}

  async saveEvents(aggregateId: string, events: Event[]): Promise<void> {
    const existingEvents = this.events.get(aggregateId) || []
    const lastVersion = existingEvents.length

    const newEvents = events.map((event, index) => ({
      ...event,
      id: crypto.randomUUID(),
      timestamp: new Date(),
      version: lastVersion + index + 1
    }))

    this.events.set(aggregateId, [...existingEvents, ...newEvents])

    // Check if we should create a snapshot
    const finalVersion = lastVersion + newEvents.length
    if (this.snapshotStrategy.shouldTakeSnapshot(aggregateId, finalVersion)) {
      // This would typically reconstruct the state and create a snapshot
      console.log(`Snapshot opportunity for aggregate ${aggregateId} at version ${finalVersion}`)
    }
  }

  async getEvents(aggregateId: string): Promise<Event[]> {
    return this.events.get(aggregateId) || []
  }

  async getEventsFromVersion(aggregateId: string, fromVersion: number): Promise<Event[]> {
    const events = this.events.get(aggregateId) || []
    return events.filter(event => event.version >= fromVersion)
  }

  async getEventsWithSnapshot(aggregateId: string): Promise<{ events: Event[], snapshot: Snapshot | null }> {
    const snapshot = await this.snapshotStore.getLatestSnapshot(aggregateId)
    let events: Event[]

    if (snapshot) {
      events = await this.getEventsFromVersion(aggregateId, snapshot.version + 1)
    } else {
      events = await this.getEvents(aggregateId)
    }

    return { events, snapshot }
  }
}

// Shopping Cart State
interface CartState {
  id: string
  items: CartItem[]
  isActive: boolean
  totalAmount: number
  version: number
  lastUpdated: Date
}

interface CartItem {
  productId: string
  productName: string
  quantity: number
  unitPrice: number
}

// Shopping Cart State Reconstructor
class ShoppingCartReconstructor implements StateReconstructor<CartState> {
  reconstruct(events: Event[]): CartState {
    let state: CartState = {
      id: '',
      items: [],
      isActive: true,
      totalAmount: 0,
      version: 0,
      lastUpdated: new Date()
    }

    for (const event of events) {
      state = this.applyEvent(state, event)
    }

    return state
  }

  createSnapshot(state: CartState, version: number): Snapshot {
    return {
      aggregateId: state.id,
      data: {
        id: state.id,
        items: state.items,
        isActive: state.isActive,
        totalAmount: state.totalAmount,
        lastUpdated: state.lastUpdated
      },
      version,
      timestamp: new Date()
    }
  }

  applySnapshot(snapshot: Snapshot, events: Event[]): CartState {
    let state: CartState = {
      ...snapshot.data,
      version: snapshot.version
    }

    for (const event of events) {
      state = this.applyEvent(state, event)
    }

    return state
  }

  private applyEvent(state: CartState, event: Event): CartState {
    const newState = { ...state, version: event.version, lastUpdated: event.timestamp }

    switch (event.type) {
      case 'CART_CREATED':
        return {
          ...newState,
          id: event.aggregateId,
          items: [],
          isActive: true,
          totalAmount: 0
        }

      case 'ITEM_ADDED':
        const existingItem = newState.items.find(item => item.productId === event.data.productId)
        let updatedItems: CartItem[]

        if (existingItem) {
          updatedItems = newState.items.map(item =>
            item.productId === event.data.productId
              ? { ...item, quantity: item.quantity + event.data.quantity }
              : item
          )
        } else {
          updatedItems = [
            ...newState.items,
            {
              productId: event.data.productId,
              productName: event.data.productName,
              quantity: event.data.quantity,
              unitPrice: event.data.unitPrice
            }
          ]
        }

        return {
          ...newState,
          items: updatedItems,
          totalAmount: this.calculateTotalAmount(updatedItems)
        }

      case 'ITEM_REMOVED':
        const filteredItems = newState.items.filter(item => item.productId !== event.data.productId)
        return {
          ...newState,
          items: filteredItems,
          totalAmount: this.calculateTotalAmount(filteredItems)
        }

      case 'CART_CHECKED_OUT':
        return {
          ...newState,
          isActive: false
        }

      case 'CART_ABANDONED':
        return {
          ...newState,
          isActive: false
        }

      default:
        return newState
    }
  }

  private calculateTotalAmount(items: CartItem[]): number {
    return items.reduce((total, item) => total + (item.quantity * item.unitPrice), 0)
  }
}

// State Reconstruction Service
class StateReconstructionService {
  constructor(
    private eventStore: EnhancedEventStore,
    private snapshotStore: SnapshotStore,
    private snapshotStrategy: SnapshotStrategy
  ) {}

  async reconstructState<T>(
    aggregateId: string,
    reconstructor: StateReconstructor<T>
  ): Promise<T> {
    // Try to get the latest snapshot first
    const { events, snapshot } = await this.eventStore.getEventsWithSnapshot(aggregateId)

    if (snapshot) {
      console.log(`Found snapshot for ${aggregateId} at version ${snapshot.version}`)
      return reconstructor.applySnapshot(snapshot, events)
    } else {
      console.log(`No snapshot found for ${aggregateId}, reconstructing from all events`)
      return reconstructor.reconstruct(events)
    }
  }

  async reconstructStateAtVersion<T>(
    aggregateId: string,
    targetVersion: number,
    reconstructor: StateReconstructor<T>
  ): Promise<T> {
    // Try to find a snapshot before the target version
    const snapshot = await this.snapshotStore.getSnapshotBeforeVersion(aggregateId, targetVersion)

    if (snapshot) {
      const events = await this.eventStore.getEventsFromVersion(aggregateId, snapshot.version + 1)
      const relevantEvents = events.filter(event => event.version <= targetVersion)
      return reconstructor.applySnapshot(snapshot, relevantEvents)
    } else {
      const allEvents = await this.eventStore.getEvents(aggregateId)
      const relevantEvents = allEvents.filter(event => event.version <= targetVersion)
      return reconstructor.reconstruct(relevantEvents)
    }
  }

  async createSnapshot<T>(
    aggregateId: string,
    reconstructor: StateReconstructor<T>
  ): Promise<void> {
    const events = await this.eventStore.getEvents(aggregateId)

    if (events.length === 0) {
      throw new Error('No events found for aggregate')
    }

    const state = reconstructor.reconstruct(events)
    const latestEvent = events[events.length - 1]

    const snapshot = reconstructor.createSnapshot(state, latestEvent.version)
    await this.snapshotStore.saveSnapshot(snapshot)

    console.log(`Created snapshot for ${aggregateId} at version ${latestEvent.version}`)
  }

  async getReconstructionMetrics(aggregateId: string): Promise<{
    totalEvents: number
    hasSnapshot: boolean
    snapshotVersion?: number
    eventsSinceSnapshot: number
  }> {
    const { events, snapshot } = await this.eventStore.getEventsWithSnapshot(aggregateId)

    return {
      totalEvents: events.length + (snapshot ? 1 : 0),
      hasSnapshot: !!snapshot,
      snapshotVersion: snapshot?.version,
      eventsSinceSnapshot: events.length
    }
  }
}

// Performance Comparison Utility
class ReconstructionPerformanceTester {
  async compareReconstructionMethods(
    aggregateId: string,
    reconstructor: StateReconstructor<any>,
    eventStore: EnhancedEventStore,
    reconstructionService: StateReconstructionService
  ): Promise<{
    fullReconstructionTime: number
    snapshotReconstructionTime: number
    performanceGain: number
  }> {
    // Measure full reconstruction
    const fullStart = performance.now()
    const allEvents = await eventStore.getEvents(aggregateId)
    await reconstructor.reconstruct(allEvents)
    const fullEnd = performance.now()
    const fullReconstructionTime = fullEnd - fullStart

    // Measure snapshot-based reconstruction
    const snapshotStart = performance.now()
    await reconstructionService.reconstructState(aggregateId, reconstructor)
    const snapshotEnd = performance.now()
    const snapshotReconstructionTime = snapshotEnd - snapshotStart

    const performanceGain = fullReconstructionTime / snapshotReconstructionTime

    return {
      fullReconstructionTime,
      snapshotReconstructionTime,
      performanceGain
    }
  }
}

// Usage Example
async function stateReconstructionExample() {
  const snapshotStore = new SnapshotStore()
  const snapshotStrategy = new IntervalSnapshotStrategy(10) // Snapshot every 10 events
  const eventStore = new EnhancedEventStore(new Map(), snapshotStore, snapshotStrategy)
  const reconstructor = new ShoppingCartReconstructor()
  const reconstructionService = new StateReconstructionService(eventStore, snapshotStore, snapshotStrategy)

  const aggregateId = 'cart-123'

  // Simulate adding many events to the cart
  const events: Event[] = [
    {
      id: crypto.randomUUID(),
      aggregateId,
      type: 'CART_CREATED',
      data: {},
      timestamp: new Date(),
      version: 1
    }
  ]

  // Add 25 items to create many events
  for (let i = 1; i <= 25; i++) {
    events.push({
      id: crypto.randomUUID(),
      aggregateId,
      type: 'ITEM_ADDED',
      data: {
        productId: `prod-${i}`,
        productName: `Product ${i}`,
        quantity: 1,
        unitPrice: 10 * i
      },
      timestamp: new Date(),
      version: i + 1
    })
  }

  await eventStore.saveEvents(aggregateId, events)

  // Create a snapshot at current state
  await reconstructionService.createSnapshot(aggregateId, reconstructor)

  // Add more events after snapshot
  const moreEvents: Event[] = []
  for (let i = 26; i <= 35; i++) {
    moreEvents.push({
      id: crypto.randomUUID(),
      aggregateId,
      type: 'ITEM_ADDED',
      data: {
        productId: `prod-${i}`,
        productName: `Product ${i}`,
        quantity: 1,
        unitPrice: 10 * i
      },
      timestamp: new Date(),
      version: i + 1
    })
  }

  await eventStore.saveEvents(aggregateId, moreEvents)

  // Get reconstruction metrics
  const metrics = await reconstructionService.getReconstructionMetrics(aggregateId)
  console.log('Reconstruction metrics:', metrics)

  // Reconstruct state using snapshot optimization
  const cartState = await reconstructionService.reconstructState(aggregateId, reconstructor)
  console.log('Reconstructed cart state:', {
    id: cartState.id,
    itemCount: cartState.items.length,
    totalAmount: cartState.totalAmount,
    isActive: cartState.isActive,
    version: cartState.version
  })

  // Performance comparison
  const performanceTester = new ReconstructionPerformanceTester()
  const performance = await performanceTester.compareReconstructionMethods(
    aggregateId,
    reconstructor,
    eventStore,
    reconstructionService
  )

  console.log('Performance comparison:', {
    fullReconstruction: `${performance.fullReconstructionTime.toFixed(2)}ms`,
    snapshotReconstruction: `${performance.snapshotReconstructionTime.toFixed(2)}ms`,
    performanceGain: `${performance.performanceGain.toFixed(2)}x faster`
  })
}

export {
  Event,
  Snapshot,
  StateReconstructor,
  SnapshotStrategy,
  IntervalSnapshotStrategy,
  SnapshotStore,
  EnhancedEventStore,
  CartState,
  ShoppingCartReconstructor,
  StateReconstructionService,
  stateReconstructionExample
}
        

// Event Versioning System
interface EventSchema {
  type: string
  version: number
  schema: any
}

interface EventTransformer {
  fromVersion: number
  toVersion: number
  transform(event: any): any
}

interface VersionedEvent {
  id: string
  aggregateId: string
  type: string
  data: any
  timestamp: Date
  version: number
  eventVersion: number
}

// Schema Registry
class SchemaRegistry {
  private schemas: Map<string, EventSchema[]> = new Map()
  private transformers: Map<string, EventTransformer[]> = new Map()

  registerSchema(eventType: string, version: number, schema: any): void {
    const schemas = this.schemas.get(eventType) || []
    schemas.push({ type: eventType, version, schema })
    this.schemas.set(eventType, schemas)
  }

  registerTransformer(eventType: string, transformer: EventTransformer): void {
    const transformers = this.transformers.get(eventType) || []
    transformers.push(transformer)
    this.transformers.set(eventType, transformers)
  }

  getLatestVersion(eventType: string): number {
    const schemas = this.schemas.get(eventType) || []
    if (schemas.length === 0) {
      throw new Error(`No schema found for event type: ${eventType}`)
    }
    return Math.max(...schemas.map(s => s.version))
  }

  getSchema(eventType: string, version: number): EventSchema | null {
    const schemas = this.schemas.get(eventType) || []
    return schemas.find(s => s.version === version) || null
  }

  getTransformers(eventType: string): EventTransformer[] {
    return this.transformers.get(eventType) || []
  }

  getTransformationPath(eventType: string, fromVersion: number, toVersion: number): EventTransformer[] {
    const transformers = this.getTransformers(eventType)
    const path: EventTransformer[] = []

    let currentVersion = fromVersion
    while (currentVersion < toVersion) {
      const nextTransformer = transformers.find(t => t.fromVersion === currentVersion)
      if (!nextTransformer) {
        throw new Error(`No transformer found from version ${currentVersion} for event type ${eventType}`)
      }
      path.push(nextTransformer)
      currentVersion = nextTransformer.toVersion
    }

    return path
  }
}

// Event Upgrader
class EventUpgrader {
  constructor(private schemaRegistry: SchemaRegistry) {}

  async upgradeEvent(event: VersionedEvent, targetVersion?: number): Promise<VersionedEvent> {
    const latestVersion = targetVersion || this.schemaRegistry.getLatestVersion(event.type)

    if (event.eventVersion >= latestVersion) {
      return event // Event is already at or above target version
    }

    const transformationPath = this.schemaRegistry.getTransformationPath(
      event.type,
      event.eventVersion,
      latestVersion
    )

    let upgradedEvent = { ...event }

    for (const transformer of transformationPath) {
      upgradedEvent.data = transformer.transform(upgradedEvent.data)
      upgradedEvent.eventVersion = transformer.toVersion
    }

    return upgradedEvent
  }

  async upgradeEvents(events: VersionedEvent[]): Promise<VersionedEvent[]> {
    const upgradedEvents: VersionedEvent[] = []

    for (const event of events) {
      try {
        const upgraded = await this.upgradeEvent(event)
        upgradedEvents.push(upgraded)
      } catch (error) {
        console.error(`Failed to upgrade event ${event.id}:`, error)
        // Keep original event if upgrade fails
        upgradedEvents.push(event)
      }
    }

    return upgradedEvents
  }
}

// Event Validation
class EventValidator {
  constructor(private schemaRegistry: SchemaRegistry) {}

  validateEvent(event: VersionedEvent): { isValid: boolean; errors: string[] } {
    const schema = this.schemaRegistry.getSchema(event.type, event.eventVersion)
    if (!schema) {
      return {
        isValid: false,
        errors: [`No schema found for event type ${event.type} version ${event.eventVersion}`]
      }
    }

    return this.validateAgainstSchema(event.data, schema.schema)
  }

  private validateAgainstSchema(data: any, schema: any): { isValid: boolean; errors: string[] } {
    const errors: string[] = []

    // Simple validation logic (in production, use a proper JSON schema validator)
    if (schema.type === 'object' && schema.properties) {
      for (const [key, propSchema] of Object.entries(schema.properties as any)) {
        if (schema.required?.includes(key) && !(key in data)) {
          errors.push(`Missing required property: ${key}`)
        }

        if (key in data) {
          const propErrors = this.validateProperty(data[key], propSchema)
          errors.push(...propErrors.map(e => `${key}: ${e}`))
        }
      }
    }

    return {
      isValid: errors.length === 0,
      errors
    }
  }

  private validateProperty(value: any, schema: any): string[] {
    const errors: string[] = []

    if (schema.type && typeof value !== schema.type) {
      errors.push(`Expected type ${schema.type}, got ${typeof value}`)
    }

    return errors
  }
}

// Example Event Schemas

// V1: ItemAdded event with simple structure
const ItemAddedV1Schema = {
  type: 'object',
  properties: {
    productId: { type: 'string' },
    quantity: { type: 'number' },
    unitPrice: { type: 'number' }
  },
  required: ['productId', 'quantity', 'unitPrice']
}

// V2: ItemAdded event with additional productName field
const ItemAddedV2Schema = {
  type: 'object',
  properties: {
    productId: { type: 'string' },
    productName: { type: 'string' },
    quantity: { type: 'number' },
    unitPrice: { type: 'number' },
    discount: { type: 'number', minimum: 0, maximum: 1 }
  },
  required: ['productId', 'productName', 'quantity', 'unitPrice']
}

// V3: ItemAdded event with category and metadata
const ItemAddedV3Schema = {
  type: 'object',
  properties: {
    productId: { type: 'string' },
    productName: { type: 'string' },
    quantity: { type: 'number' },
    unitPrice: { type: 'number' },
    discount: { type: 'number', minimum: 0, maximum: 1 },
    category: { type: 'string' },
    metadata: { type: 'object' }
  },
  required: ['productId', 'productName', 'quantity', 'unitPrice', 'category']
}

// Event Transformers

// V1 to V2: Add productName based on productId lookup
class ItemAddedV1ToV2Transformer implements EventTransformer {
  fromVersion = 1
  toVersion = 2

  // In a real implementation, this would query a product catalog
  private productNames: Record<string, string> = {
    'prod-1': 'Laptop',
    'prod-2': 'Mouse',
    'prod-3': 'Keyboard'
  }

  transform(event: any): any {
    return {
      ...event,
      productName: this.productNames[event.productId] || 'Unknown Product',
      discount: event.discount || 0
    }
  }
}

// V2 to V3: Add category and metadata
class ItemAddedV2ToV3Transformer implements EventTransformer {
  fromVersion = 2
  toVersion = 3

  // Simple categorization based on product ID patterns
  private getProductCategory(productId: string): string {
    if (productId.includes('laptop')) return 'Electronics'
    if (productId.includes('mouse') || productId.includes('keyboard')) return 'Accessories'
    return 'General'
  }

  transform(event: any): any {
    return {
      ...event,
      category: this.getProductCategory(event.productId),
      metadata: {
        source: 'legacy-system',
        migratedAt: new Date().toISOString()
      }
    }
  }
}

// V2 to V4: Remove discount, add pricing breakdown
class ItemAddedV3ToV4Transformer implements EventTransformer {
  fromVersion = 3
  toVersion = 4

  transform(event: any): any {
    const discountAmount = event.unitPrice * event.quantity * (event.discount || 0)
    const finalPrice = event.unitPrice - (event.unitPrice * (event.discount || 0))

    return {
      productId: event.productId,
      productName: event.productName,
      quantity: event.quantity,
      unitPrice: event.unitPrice,
      finalPrice,
      discountAmount,
      category: event.category,
      metadata: {
        ...event.metadata,
        pricing: {
          originalUnitPrice: event.unitPrice,
          discountPercentage: event.discount || 0,
          discountAmount,
          finalUnitPrice: finalPrice
        }
      }
    }
  }
}

const ItemAddedV4Schema = {
  type: 'object',
  properties: {
    productId: { type: 'string' },
    productName: { type: 'string' },
    quantity: { type: 'number' },
    unitPrice: { type: 'number' },
    finalPrice: { type: 'number' },
    discountAmount: { type: 'number' },
    category: { type: 'string' },
    metadata: {
      type: 'object',
      properties: {
        source: { type: 'string' },
        migratedAt: { type: 'string' },
        pricing: {
          type: 'object',
          properties: {
            originalUnitPrice: { type: 'number' },
            discountPercentage: { type: 'number' },
            discountAmount: { type: 'number' },
            finalUnitPrice: { type: 'number' }
          }
        }
      }
    }
  },
  required: ['productId', 'productName', 'quantity', 'unitPrice', 'finalPrice', 'category']
}

// Versioned Event Store
class VersionedEventStore {
  private events: Map<string, VersionedEvent[]> = new Map()

  constructor(
    private schemaRegistry: SchemaRegistry,
    private eventUpgrader: EventUpgrader,
    private eventValidator: EventValidator
  ) {}

  async saveEvent(event: VersionedEvent): Promise<void> {
    // Validate event against its schema
    const validation = this.eventValidator.validateEvent(event)
    if (!validation.isValid) {
      throw new Error(`Event validation failed: ${validation.errors.join(', ')}`)
    }

    const aggregateEvents = this.events.get(event.aggregateId) || []
    aggregateEvents.push(event)
    this.events.set(event.aggregateId, aggregateEvents)
  }

  async getEvents(aggregateId: string, targetVersion?: number): Promise<VersionedEvent[]> {
    const events = this.events.get(aggregateId) || []

    if (!targetVersion) {
      return events
    }

    // Upgrade events to target version
    const upgradedEvents: VersionedEvent[] = []
    for (const event of events) {
      const upgraded = await this.eventUpgrader.upgradeEvent(event, targetVersion)
      upgradedEvents.push(upgraded)
    }

    return upgradedEvents
  }

  async getLatestEvents(aggregateId: string): Promise<VersionedEvent[]> {
    const events = this.events.get(aggregateId) || []
    const latestVersion = Math.max(...events.map(e => this.schemaRegistry.getLatestVersion(e.type)))
    return this.getEvents(aggregateId, latestVersion)
  }

  async migrateEvents(aggregateId: string): Promise<{
    totalEvents: number
    upgradedEvents: number
    errors: string[]
  }> {
    const events = this.events.get(aggregateId) || []
    const errors: string[] = []
    let upgradedCount = 0

    const upgradedEvents = await this.eventUpgrader.upgradeEvents(events)

    // Validate upgraded events
    for (const event of upgradedEvents) {
      const validation = this.eventValidator.validateEvent(event)
      if (!validation.isValid) {
        errors.push(`Event ${event.id}: ${validation.errors.join(', ')}`)
      } else if (event.eventVersion !== this.schemaRegistry.getLatestVersion(event.type)) {
        upgradedCount++
      }
    }

    // Store upgraded events
    this.events.set(aggregateId, upgradedEvents)

    return {
      totalEvents: events.length,
      upgradedEvents: upgradedCount,
      errors
    }
  }
}

// Event Versioning Analytics
class EventVersioningAnalytics {
  constructor(
    private eventStore: VersionedEventStore,
    private schemaRegistry: SchemaRegistry
  ) {}

  async getVersionDistribution(aggregateId?: string): Promise<Array<{
    eventType: string
    versionDistribution: Record<number, number>
    totalEvents: number
  }>> {
    // This would analyze all events in the store
    // For demo purposes, return sample data
    return [
      {
        eventType: 'ITEM_ADDED',
        versionDistribution: {
          1: 10,
          2: 25,
          3: 15
        },
        totalEvents: 50
      },
      {
        eventType: 'ITEM_REMOVED',
        versionDistribution: {
          1: 5,
          2: 8
        },
        totalEvents: 13
      }
    ]
  }

  async getMigrationReport(aggregateId: string): Promise<{
    eventsMigrated: number
    eventsWithErrors: number
    errorDetails: string[]
  }> {
    const migration = await this.eventStore.migrateEvents(aggregateId)

    return {
      eventsMigrated: migration.upgradedEvents,
      eventsWithErrors: migration.errors.length,
      errorDetails: migration.errors
    }
  }

  async getSchemaEvolutionTimeline(eventType: string): Promise<Array<{
    version: number
    introducedAt: Date
    changes: string[]
  }>> {
    // This would track when each schema version was introduced
    return [
      {
        version: 1,
        introducedAt: new Date('2023-01-01'),
        changes: ['Initial version', 'Basic item data']
      },
      {
        version: 2,
        introducedAt: new Date('2023-06-01'),
        changes: ['Added productName field', 'Added optional discount']
      },
      {
        version: 3,
        introducedAt: new Date('2024-01-01'),
        changes: ['Added category field', 'Added metadata object']
      }
    ]
  }
}

// Setup and Usage Example
async function setupEventVersioning() {
  const schemaRegistry = new SchemaRegistry()

  // Register schemas
  schemaRegistry.registerSchema('ITEM_ADDED', 1, ItemAddedV1Schema)
  schemaRegistry.registerSchema('ITEM_ADDED', 2, ItemAddedV2Schema)
  schemaRegistry.registerSchema('ITEM_ADDED', 3, ItemAddedV3Schema)
  schemaRegistry.registerSchema('ITEM_ADDED', 4, ItemAddedV4Schema)

  // Register transformers
  schemaRegistry.registerTransformer('ITEM_ADDED', new ItemAddedV1ToV2Transformer())
  schemaRegistry.registerTransformer('ITEM_ADDED', new ItemAddedV2ToV3Transformer())
  schemaRegistry.registerTransformer('ITEM_ADDED', new ItemAddedV3ToV4Transformer())

  const eventUpgrader = new EventUpgrader(schemaRegistry)
  const eventValidator = new EventValidator(schemaRegistry)
  const eventStore = new VersionedEventStore(schemaRegistry, eventUpgrader, eventValidator)
  const analytics = new EventVersioningAnalytics(eventStore, schemaRegistry)

  return { eventStore, analytics, schemaRegistry }
}

async function eventVersioningExample() {
  const { eventStore, analytics, schemaRegistry } = await setupEventVersioning()

  // Create sample events with different versions
  const aggregateId = 'cart-123'

  const events: VersionedEvent[] = [
    {
      id: crypto.randomUUID(),
      aggregateId,
      type: 'ITEM_ADDED',
      data: {
        productId: 'prod-1',
        quantity: 1,
        unitPrice: 999.99
      },
      timestamp: new Date('2023-05-01'),
      version: 1,
      eventVersion: 1 // V1 schema
    },
    {
      id: crypto.randomUUID(),
      aggregateId,
      type: 'ITEM_ADDED',
      data: {
        productId: 'prod-2',
        productName: 'Wireless Mouse',
        quantity: 2,
        unitPrice: 29.99,
        discount: 0.1
      },
      timestamp: new Date('2023-07-01'),
      version: 2,
      eventVersion: 2 // V2 schema
    },
    {
      id: crypto.randomUUID(),
      aggregateId,
      type: 'ITEM_ADDED',
      data: {
        productId: 'prod-3',
        productName: 'Mechanical Keyboard',
        quantity: 1,
        unitPrice: 149.99,
        discount: 0.05,
        category: 'Accessories',
        metadata: {
          source: 'web-app',
          addedBy: 'user-456'
        }
      },
      timestamp: new Date('2024-02-01'),
      version: 3,
      eventVersion: 3 // V3 schema
    }
  ]

  // Save events (validation will occur)
  for (const event of events) {
    try {
      await eventStore.saveEvent(event)
      console.log(`Saved event ${event.id} with version ${event.eventVersion}`)
    } catch (error) {
      console.error(`Failed to save event ${event.id}:`, error)
    }
  }

  // Get events in their original versions
  console.log('\n=== Original Events ===')
  const originalEvents = await eventStore.getEvents(aggregateId)
  originalEvents.forEach(event => {
    console.log(`Event ${event.id}: version ${event.eventVersion}, data:`, event.data)
  })

  // Get events upgraded to latest version
  console.log('\n=== Upgraded Events (Latest Version) ===')
  const latestEvents = await eventStore.getLatestEvents(aggregateId)
  latestEvents.forEach(event => {
    console.log(`Event ${event.id}: version ${event.eventVersion}, data:`, event.data)
  })

  // Get events upgraded to specific version
  console.log('\n=== Events Upgraded to V2 ===')
  const v2Events = await eventStore.getEvents(aggregateId, 2)
  v2Events.forEach(event => {
    console.log(`Event ${event.id}: version ${event.eventVersion}, data:`, event.data)
  })

  // Migration report
  console.log('\n=== Migration Report ===')
  const migrationReport = await analytics.getMigrationReport(aggregateId)
  console.log('Migration report:', migrationReport)

  // Version distribution
  console.log('\n=== Version Distribution ===')
  const versionDistribution = await analytics.getVersionDistribution()
  versionDistribution.forEach(dist => {
    console.log(`Event type ${dist.eventType}:`, dist.versionDistribution)
  })

  // Schema evolution timeline
  console.log('\n=== Schema Evolution Timeline ===')
  const timeline = await analytics.getSchemaEvolutionTimeline('ITEM_ADDED')
  timeline.forEach(entry => {
    console.log(`Version ${entry.version} (${entry.introducedAt.toISOString().split('T')[0]}):`, entry.changes)
  })
}

export {
  VersionedEvent,
  EventSchema,
  EventTransformer,
  SchemaRegistry,
  EventUpgrader,
  EventValidator,
  VersionedEventStore,
  EventVersioningAnalytics,
  ItemAddedV1ToV2Transformer,
  ItemAddedV2ToV3Transformer,
  ItemAddedV3ToV4Transformer,
  setupEventVersioning,
  eventVersioningExample
}