Akka Cluster Sharding

import akka.cluster.sharding.ClusterSharding
import akka.cluster.sharding.ClusterShardingSettings
import akka.cluster.sharding.ShardRegion
import akka.cluster.sharding.ShardCoordinator.ShardAllocationStrategy

import akka.actor.{ActorSystem, Props}
import akka.cluster.sharding.{ClusterSharding, ClusterShardingSettings, ShardRegion}
import akka.cluster.sharding.ShardCoordinator.ShardAllocationStrategy

implicit val system: ActorSystem = ActorSystem("MyClusterSystem")

// Define entity extraction functions
val extractEntityId: ShardRegion.ExtractEntityId = {
  case msg @ MyEntityMessage(entityId, _) => (entityId, msg)
}

val extractShardId: ShardRegion.ExtractShardId = {
  case MyEntityMessage(entityId, _) => (entityId.hashCode % 100).toString
}

// Start cluster sharding for an entity type
val shardRegion = ClusterSharding(system).start(
  typeName = "MyEntity",
  entityProps = Props[MyEntityActor](),
  settings = ClusterShardingSettings(system),
  extractEntityId = extractEntityId,
  extractShardId = extractShardId
)

// Send messages to entities
shardRegion ! MyEntityMessage("entity-1", "Hello World")

object ClusterSharding extends ExtensionId[ClusterSharding] with ExtensionIdProvider {
  def get(system: ActorSystem): ClusterSharding
  def get(system: ClassicActorSystemProvider): ClusterSharding
}

class ClusterSharding(system: ExtendedActorSystem) extends Extension {
  // Full configuration start methods
  def start(
    typeName: String,
    entityProps: Props,
    settings: ClusterShardingSettings,
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId,
    allocationStrategy: ShardAllocationStrategy,
    handOffStopMessage: Any
  ): ActorRef
  
  def start(
    typeName: String,
    entityProps: Props,
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId,
    allocationStrategy: ShardAllocationStrategy,
    handOffStopMessage: Any
  ): ActorRef
  
  // Simplified start methods with defaults
  def start(
    typeName: String,
    entityProps: Props,
    settings: ClusterShardingSettings,
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId
  ): ActorRef
  
  def start(
    typeName: String,
    entityProps: Props,
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId
  ): ActorRef
  
  // Java API start methods
  def start(
    typeName: String,
    entityProps: Props,
    settings: ClusterShardingSettings,
    messageExtractor: ShardRegion.MessageExtractor,
    allocationStrategy: ShardAllocationStrategy,
    handOffStopMessage: Any
  ): ActorRef
  
  def start(
    typeName: String,
    entityProps: Props,
    settings: ClusterShardingSettings,
    messageExtractor: ShardRegion.MessageExtractor
  ): ActorRef
  
  def start(
    typeName: String,
    entityProps: Props,
    messageExtractor: ShardRegion.MessageExtractor
  ): ActorRef
  
  // Proxy start methods
  def startProxy(
    typeName: String,
    role: Option[String],
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId
  ): ActorRef
  
  def startProxy(
    typeName: String,
    role: Option[String],
    dataCenter: Option[DataCenter],
    extractEntityId: ShardRegion.ExtractEntityId,
    extractShardId: ShardRegion.ExtractShardId
  ): ActorRef
  
  def startProxy(
    typeName: String,
    role: Optional[String],
    messageExtractor: ShardRegion.MessageExtractor
  ): ActorRef
  
  def startProxy(
    typeName: String,
    role: Optional[String],
    dataCenter: Optional[String],
    messageExtractor: ShardRegion.MessageExtractor
  ): ActorRef
  
  // Access methods
  def shardRegion(typeName: String): ActorRef
  def shardRegionProxy(typeName: String, dataCenter: DataCenter): ActorRef
  def shardTypeNames: Set[String]
  def getShardTypeNames: java.util.Set[String]
  def defaultShardAllocationStrategy(settings: ClusterShardingSettings): ShardAllocationStrategy
}

object ShardRegion {
  // Type aliases
  type EntityId = String
  type ShardId = String
  type Msg = Any
  type ExtractEntityId = PartialFunction[Msg, (EntityId, Msg)]
  type ExtractShardId = Msg => ShardId
  
  // Message extractor interface
  trait MessageExtractor {
    def entityId(message: Any): String
    def entityMessage(message: Any): Any
    def shardId(message: Any): String
  }
  
  // Hash-based message extractor
  abstract class HashCodeMessageExtractor(maxNumberOfShards: Int) extends MessageExtractor {
    def entityMessage(message: Any): Any = message
    def shardId(message: Any): String
  }
  
  object HashCodeMessageExtractor {
    def shardId(id: String, maxNumberOfShards: Int): String
  }
  
  // Command messages
  sealed trait ShardRegionCommand
  case class Passivate(stopMessage: Any) extends ShardRegionCommand
  case object GracefulShutdown extends ShardRegionCommand
  def gracefulShutdownInstance: GracefulShutdown.type
  
  // Entity lifecycle
  case class ShardInitialized(shardId: ShardId)
  case class StartEntity(entityId: EntityId)
  
  // Query messages
  sealed trait ShardRegionQuery
  case object GetCurrentRegions extends ShardRegionQuery
  def getCurrentRegionsInstance: GetCurrentRegions.type
  case class GetClusterShardingStats(timeout: FiniteDuration) extends ShardRegionQuery
  case object GetShardRegionStats extends ShardRegionQuery
  def getRegionStatsInstance: GetShardRegionStats.type
  case object GetShardRegionState extends ShardRegionQuery
  def getShardRegionStateInstance: GetShardRegionState.type
  
  // Response messages
  case class CurrentRegions(regions: Set[Address]) {
    def getRegions: java.util.Set[Address]
  }
  
  case class ClusterShardingStats(regions: Map[Address, ShardRegionStats]) {
    def getRegions(): java.util.Map[Address, ShardRegionStats]
  }
  
  class ShardRegionStats(val stats: Map[ShardId, Int], val failed: Set[ShardId]) {
    def this(stats: Map[ShardId, Int])
    def getStats(): java.util.Map[ShardId, Int]
    def getFailed(): java.util.Set[ShardId]
  }
  
  object ShardRegionStats extends AbstractFunction1[Map[ShardId, Int], ShardRegionStats] {
    def apply(stats: Map[ShardId, Int]): ShardRegionStats
    def apply(stats: Map[ShardId, Int], failed: Set[ShardId]): ShardRegionStats
  }
  
  class CurrentShardRegionState(val shards: Set[ShardState], val failed: Set[ShardId]) {
    def this(shards: Set[ShardState])
    def getShards(): java.util.Set[ShardState]
    def getFailed(): java.util.Set[ShardId]
  }
  
  object CurrentShardRegionState extends AbstractFunction1[Set[ShardState], CurrentShardRegionState] {
    def apply(shards: Set[ShardState]): CurrentShardRegionState
    def apply(shards: Set[ShardState], failed: Set[ShardId]): CurrentShardRegionState
  }
  
  case class ShardState(shardId: ShardId, entityIds: Set[EntityId]) {
    def getEntityIds(): java.util.Set[EntityId]
  }
}

object ClusterShardingSettings {
  def apply(system: ActorSystem): ClusterShardingSettings
  def apply(config: Config): ClusterShardingSettings
  
  val StateStoreModePersistence = "persistence"
  val StateStoreModeDData = "ddata"
}

class ClusterShardingSettings(
  role: Option[String],
  rememberEntities: Boolean,
  stateStoreMode: String,
  tuningParameters: TuningParameters
)

object ShardCoordinator {
  type ShardId = String
  
  trait ShardAllocationStrategy {
    def allocateShard(
      requester: ActorRef,
      shardId: ShardId,
      currentShardAllocations: Map[ActorRef, IndexedSeq[ShardId]]
    ): Future[ActorRef]
    
    def rebalance(
      currentShardAllocations: Map[ActorRef, IndexedSeq[ShardId]],
      rebalanceInProgress: Set[ShardId]
    ): Future[Set[ShardId]]
  }
  
  // Factory methods for built-in strategies
  def leastShardAllocationStrategy(
    absoluteLimit: Int,
    relativeLimit: Double
  ): ShardAllocationStrategy
  
  class LeastShardAllocationStrategy(
    rebalanceThreshold: Int,
    maxSimultaneousRebalance: Int
  ) extends ShardAllocationStrategy
}

object ShardAllocationStrategy {
  def leastShardAllocationStrategy(
    absoluteLimit: Int,
    relativeLimit: Double
  ): ShardAllocationStrategy
}

object ExternalShardAllocation extends ExtensionId[ExternalShardAllocation] with ExtensionIdProvider {
  def get(system: ClassicActorSystemProvider): ExternalShardAllocation
}

class ExternalShardAllocation(system: ExtendedActorSystem) extends Extension {
  def clientFor(typeName: String): scaladsl.ExternalShardAllocationClient
  def getClient(typeName: String): javadsl.ExternalShardAllocationClient
}

// Scala API
package scaladsl {
  trait ExternalShardAllocationClient {
    def updateShardLocation(shard: ShardId, location: Address): Future[Done]
    def updateShardLocations(locations: Map[ShardId, Address]): Future[Done] 
    def shardLocations(): Future[ShardLocations]
  }
}

// Java API  
package javadsl {
  trait ExternalShardAllocationClient {
    def updateShardLocation(shard: ShardId, location: Address): CompletionStage[Done]
    def updateShardLocations(locations: java.util.Map[ShardId, Address]): CompletionStage[Done]
    def shardLocations(): CompletionStage[ShardLocations]
  }
}

// Response type
case class ShardLocations(locations: Map[ShardId, Address]) {
  def getLocations(): java.util.Map[ShardId, Address]
}

// Health checking
class ClusterShardingHealthCheck extends HealthCheck {
  def isHealthy(): Boolean
}

// Observability and monitoring
class ShardingFlightRecorder extends Extension {
  def recordShardAllocation(typeName: String, shardId: ShardId, node: Address): Unit
  def recordShardRebalance(typeName: String, shardId: ShardId, from: Address, to: Address): Unit
}

object ShardingFlightRecorder extends ExtensionId[ShardingFlightRecorder] with ExtensionIdProvider {
  def get(system: ActorSystem): ShardingFlightRecorder
  def get(system: ClassicActorSystemProvider): ShardingFlightRecorder
}

trait ClusterShardingSerializable

object RemoveInternalClusterShardingData

// Entity and Shard identifiers
type EntityId = String
type ShardId = String
type Msg = Any

// Message extraction types
type ExtractEntityId = PartialFunction[Msg, (EntityId, Msg)]
type ExtractShardId = Msg => ShardId

// Core sharding components
trait Extension
trait ExtensionId[T <: Extension] {
  def get(system: ActorSystem): T
  def get(system: ClassicActorSystemProvider): T
}
trait ExtensionIdProvider

// Actor system integration
class ActorRef
class Props
class ActorSystem
class ExtendedActorSystem
trait ClassicActorSystemProvider

// Cluster integration
class Address
class Cluster
trait DataCenter
class Member

// Message types
trait ClusterShardingSerializable
trait ShardRegionCommand
trait ShardRegionQuery
trait NoSerializationVerificationNeeded

// Configuration types
class Config
class FiniteDuration
class ClusterSingletonManagerSettings

// Async types
class Future[T]
class Done
class CompletionStage[T]

// Health and monitoring
trait HealthCheck {
  def isHealthy(): Boolean
}

// Collections
trait Set[T] {
  def asJava: java.util.Set[T]
}
trait Map[K, V] {
  def asJava: java.util.Map[K, V]
}
trait IndexedSeq[T]

// Java interop
class Optional[T] {
  def orElse(other: T): T
}

// Utility functions
abstract class AbstractFunction1[T1, R] extends (T1 => R)

// Exception types
class IllegalStateException extends RuntimeException
class NoSuchElementException extends RuntimeException