diff --git a/api/src/lu/foyer/App.scala b/api/src/lu/foyer/App.scala
index 3a0e69b..ad174d9 100644
--- a/api/src/lu/foyer/App.scala
+++ b/api/src/lu/foyer/App.scala
@@ -15,8 +15,25 @@ import java.net.URI
 import java.time.LocalDate
 import java.util.UUID
 
-object App extends ZIOAppDefault:
-  val openAPI = OpenAPIGen.fromEndpoints(ClientController.endpoints)
-  val routes  = ClientController.routes ++ SwaggerUI.routes("docs" / "openapi", openAPI)
+object HttpServer:
+  def routes =
+    for
+      client <- ZIO.service[ClientController]
+      openAPI = OpenAPIGen.fromEndpoints(client.endpoints)
+    yield client.routes @@ Middleware.debug ++ SwaggerUI.routes("docs" / "openapi", openAPI)
 
-  override def run = Server.serve(routes).provide(Server.default)
+object App extends ZIOAppDefault:
+  val app =
+    for
+      routes <- HttpServer.routes
+      server <- Server.serve(routes).provide(Server.default)
+    yield server
+
+  override def run = app.provide(
+    CommandEngine.layer[ClientCommand, ClientEvent, ClientState],
+    ClientHandlers.layer,
+    ClientReducer.layer,
+    ClientEventRepositoryInMemory.layer,
+    ClientStateRepositoryInMemory.layer,
+    ClientController.layer
+  )
diff --git a/api/src/lu/foyer/CommandEngineController.scala b/api/src/lu/foyer/CommandEngineController.scala
new file mode 100644
index 0000000..d99a205
--- /dev/null
+++ b/api/src/lu/foyer/CommandEngineController.scala
@@ -0,0 +1,104 @@
+package lu.foyer
+
+import zio.*
+import zio.Console.*
+import zio.http.*
+import zio.http.codec.*
+import zio.http.codec.PathCodec.path
+import zio.http.endpoint.*
+import zio.schema.*
+
+import java.net.URI
+import java.time.LocalDate
+import java.util.UUID
+import lu.foyer.JsonApiResponse.One
+
+trait CommandEngineController[Command: Schema, Event: Schema, State: Schema](
+  domain: String,
+  entityName: String)
+    extends JsonApiController:
+
+  def commandEngine: CommandEngine[Command, Event, State]
+
+  val onthology = s"$domain:$entityName"
+
+  private val fetchMany =
+    Endpoint(Method.GET / entityName)
+      .query(HttpCodec.query[Page])
+      .jsonApiMany[State]
+
+  private val fetchOne =
+    Endpoint(Method.GET / entityName / uuid("entityId"))
+      .jsonApiOne[State]
+
+  private val fetchEventsMany =
+    Endpoint(Method.GET / entityName / uuid("entityId") / "events")
+      .query(HttpCodec.query[Page])
+      .jsonApiMany[Event]
+
+  private val fetchEventsOne: Endpoint[(UUID, UUID), (UUID, UUID), JsonApiResponse.Error, One[
+    Event
+  ], zio.http.endpoint.AuthType.None.type] =
+    Endpoint(Method.GET / entityName / uuid("entityId") / "events" / uuid("eventId"))
+      .jsonApiOne[Event]
+
+  private def generateCommands = commandEngine.handlers.map(handler =>
+    if handler.isCreate then generateCreateCommand(handler)
+    else generateUpdateCommand(handler)
+  )
+
+  private def generateCreateCommand(handler: CommandHandler[Command, Event, State]) =
+    given Schema[Command] = handler.commandSchema.asInstanceOf[Schema[Command]]
+    val endpoint = Endpoint(Method.POST / entityName / "commands" / handler.name)
+      .in[Command]
+      .jsonApiOne[Event]
+    val route = endpoint.implementJsonApiOneEvent(command =>
+      for
+        entityId <- Random.nextUUID
+        (event, state) <- commandEngine
+                            .handleCommand(command, handler.name, entityId)
+      yield Some(event)
+    )
+    (endpoint, route)
+
+  private def generateUpdateCommand(handler: CommandHandler[Command, Event, State]) =
+    given Schema[Command] = handler.commandSchema.asInstanceOf[Schema[Command]]
+    val endpoint = Endpoint(Method.PUT / entityName / uuid("entityId") / "commands" / handler.name)
+      .in[Command]
+      .jsonApiOne[Event]
+    val route = endpoint.implementJsonApiOneEvent((entityId, command) =>
+      for (event, _) <- commandEngine
+                          .handleCommand(command, handler.name, entityId)
+      yield Some(event)
+    )
+    (endpoint, route)
+
+  private val (commands, commandsRoutes) = generateCommands.unzip
+
+  private val fetchManyRoute =
+    fetchMany.implementJsonApiManyEntity(commandEngine.stateRepo.fetchMany)
+
+  private val fetchOneRoute =
+    fetchOne.implementJsonApiOneEntity(commandEngine.stateRepo.fetchOne)
+
+  private val fetchEventsManyRoute =
+    fetchEventsMany.implementJsonApiManyEvent(commandEngine.eventRepo.fetchMany(_, _))
+
+  private val fetchEventsOneRoute =
+    fetchEventsOne.implementJsonApiOneEvent(commandEngine.eventRepo.fetchOne(_, _))
+
+  val endpoints = List(
+    fetchMany,
+    fetchOne,
+    fetchEventsMany,
+    fetchEventsOne
+  ) ++ commands
+
+  val routes = Routes(
+    fetchManyRoute,
+    fetchOneRoute,
+    fetchEventsManyRoute,
+    fetchEventsOneRoute
+  ) ++ Routes.fromIterable(commandsRoutes)
+
+end CommandEngineController
diff --git a/api/src/lu/foyer/JsonApiController.scala b/api/src/lu/foyer/JsonApiController.scala
new file mode 100644
index 0000000..f82c873
--- /dev/null
+++ b/api/src/lu/foyer/JsonApiController.scala
@@ -0,0 +1,143 @@
+package lu.foyer
+
+import zio.*
+import zio.schema.*
+import zio.http.*
+import zio.http.codec.*
+import zio.http.codec.PathCodec.path
+import zio.http.endpoint.*
+import lu.foyer.JsonApiResponse.Many
+import lu.foyer.JsonApiResponse.One
+import java.util.UUID
+import scala.annotation.targetName
+import zio.schema.annotation.discriminatorName
+
+object JsonApiResponse:
+
+  case class One[T](
+    data: Entity[T],
+    links: Links)
+      derives Schema
+
+  case class Many[T](
+    data: List[Entity[T]],
+    links: Links,
+    meta: Meta)
+      derives Schema
+
+  case class Links(
+    self: String,
+    first: Option[String] = None,
+    prev: Option[String] = None,
+    next: Option[String] = None,
+    last: Option[String] = None)
+      derives Schema
+
+  case class Meta(totalRecords: Option[Long], totalPages: Option[Long]) derives Schema
+
+  case class Entity[T](id: UUID, `type`: String, attributes: T) derives Schema
+
+  @discriminatorName("errorType")
+  enum Error(title: String) derives Schema:
+    case NotFound(id: String)               extends Error(s"Entity $id not found")
+    case InternalServerError(title: String) extends Error(title)
+  object Error:
+    given Schema[Error.NotFound]            = DeriveSchema.gen
+    given Schema[Error.InternalServerError] = DeriveSchema.gen
+end JsonApiResponse
+
+trait JsonApiController:
+
+  def onthology: String
+
+  extension [PathInput, Input, Auth <: AuthType](
+    endpoint: Endpoint[PathInput, Input, ZNothing, ZNothing, AuthType.None]
+  )
+    def jsonApiOne[Output: Schema] =
+      endpoint
+        .out[JsonApiResponse.One[Output]]
+        .outErrors[JsonApiResponse.Error](
+          HttpCodec.error[JsonApiResponse.Error.NotFound](Status.NotFound),
+          HttpCodec.error[JsonApiResponse.Error.InternalServerError](Status.InternalServerError)
+        )
+    def jsonApiMany[Output: Schema] =
+      endpoint
+        .out[JsonApiResponse.Many[Output]]
+        .outError[JsonApiResponse.Error](Status.InternalServerError)
+
+  extension [PathInput, Input, Output, Auth <: AuthType](
+    endpoint: Endpoint[PathInput, Input, JsonApiResponse.Error, One[Output], AuthType.None]
+  )
+    def implementJsonApiOne[Env, A](
+      f: Input => RIO[Env, Option[A]],
+      getId: A => UUID,
+      getEntity: A => Output
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      endpoint.implement(input =>
+        f(input)
+          .mapError(e => JsonApiResponse.Error.InternalServerError(e.getMessage))
+          .someOrFail(JsonApiResponse.Error.NotFound(input.toString))
+          .map(item =>
+            JsonApiResponse.One(
+              JsonApiResponse.Entity(
+                id = getId(item),
+                `type` = onthology,
+                attributes = getEntity(item)
+              ),
+              JsonApiResponse.Links("https://api.example.org") // TODO
+            )
+          )
+      )
+
+    def implementJsonApiOneEntity[Env](
+      f: Input => RIO[Env, Option[Entity[Output]]]
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      implementJsonApiOne(f, _.entityId, _.data)
+
+    def implementJsonApiOneEvent[Env](
+      f: Input => RIO[Env, Option[Event[Output]]]
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      implementJsonApiOne(f, _.eventId, _.data)
+  end extension
+
+  extension [PathInput, Input, Output, Auth <: AuthType](
+    endpoint: Endpoint[PathInput, Input, JsonApiResponse.Error, Many[Output], AuthType.None]
+  )
+    def implementJsonApiMany[Env, A](
+      f: Input => RIO[Env, Paged[A]],
+      getId: A => UUID,
+      getEntity: A => Output
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      endpoint.implement(
+        f(_)
+          .map(paged =>
+            JsonApiResponse.Many(
+              paged.items.map(item =>
+                JsonApiResponse.Entity(id = getId(item), `type` = onthology, getEntity(item))
+              ),
+              JsonApiResponse.Links("https://api.example.org"),
+              meta = JsonApiResponse.Meta(paged.totals, None) // TODO
+            )
+          )
+          .mapError(e => JsonApiResponse.Error.InternalServerError(e.getMessage))
+      )
+
+    inline def implementJsonApiManyEntity[Env](
+      f: Input => RIO[Env, Paged[Entity[Output]]]
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      implementJsonApiMany(f, _.entityId, _.data)
+
+    inline def implementJsonApiManyEvent[Env](
+      f: Input => RIO[Env, Paged[Event[Output]]]
+    )(implicit trace: Trace
+    ): Route[Env, Nothing] =
+      implementJsonApiMany(f, _.eventId, _.data)
+
+  end extension
+
+end JsonApiController
diff --git a/api/src/lu/foyer/clients/ClientController.scala b/api/src/lu/foyer/clients/ClientController.scala
index d2b69a9..e312aa0 100644
--- a/api/src/lu/foyer/clients/ClientController.scala
+++ b/api/src/lu/foyer/clients/ClientController.scala
@@ -13,162 +13,12 @@ import java.net.URI
 import java.time.LocalDate
 import java.util.UUID
 
-object JsonApiResponse:
-
-  case class One[T](
-    data: Entity[T],
-    links: Links)
-      derives Schema
-
-  case class Many[T](
-    data: List[Entity[T]],
-    links: Links,
-    meta: Meta)
-      derives Schema
-
-  case class Links(
-    self: String,
-    first: Option[String] = None,
-    prev: Option[String] = None,
-    next: Option[String] = None,
-    last: Option[String] = None)
-      derives Schema
-
-  case class Meta(totalRecords: Option[Long], totalPages: Option[Long]) derives Schema
-
-  case class Entity[T](id: String, `type`: String, attributes: T) derives Schema
-
-  case class Error(message: String) derives Schema // TODO
-
-val pageParams =
-  (HttpCodec.query[Option[Int]]("page[number]")
-    & HttpCodec.query[Option[Int]]("page[size]")
-    & HttpCodec.query[Option[Boolean]]("page[totals]"))
-    .transform[Page]((number, size, totals) =>
-      Page(number.getOrElse(0), size.getOrElse(50), totals.getOrElse(false))
-    )(p => (Some(p._1), Some(p._2), Some(p._3)))
-
-trait CommandEngineController[Command: Schema, Event: Schema, State: Schema](
-  entityName: String,
-  commands: List[Command],
-  commandEngine: CommandEngine[Command, Event, State]):
-
-  private val fetchMany =
-    Endpoint(Method.GET / entityName)
-      .query(pageParams)
-      .out[JsonApiResponse.Many[State]]
-      .outError[JsonApiResponse.Error](Status.InternalServerError)
-
-  private val fetchOne =
-    Endpoint(Method.GET / entityName / string("entityId"))
-      .out[JsonApiResponse.One[State]]
-
-  private val fetchEventsMany =
-    Endpoint(Method.GET / entityName / string("entityId") / "events")
-      .query(pageParams)
-      .out[JsonApiResponse.Many[Event]]
-
-  private val fetchEventsOne =
-    Endpoint(Method.GET / entityName / string("entityId") / "events" / string("eventId"))
-      .out[JsonApiResponse.One[Event]]
-
-  private val commandsEndpoints = commands.map(command =>
-    Endpoint(Method.POST / "clients" / "commands" / command.toString.toLowerCase)
-      .in[Command]
-      .out[JsonApiResponse.One[Event]]
-  )
-
-  private val fetchManyRoute =
-    fetchMany.implement(page =>
-      commandEngine.stateRepo
-        .fetchMany(page)
-        .map(paged =>
-          JsonApiResponse.Many(
-            paged.items.map(entity =>
-              JsonApiResponse.Entity(entity.entityId.toString, "todo", entity.data)
-            ),
-            JsonApiResponse.Links("https://api.example.org"),
-            meta = JsonApiResponse.Meta(paged.totals, None) // TODO
-          )
-        ).mapError(e => JsonApiResponse.Error(e.getMessage))
+class ClientController(
+  override val commandEngine: CommandEngine[ClientCommand, ClientEvent, ClientState])
+    extends CommandEngineController[ClientCommand, ClientEvent, ClientState](
+      "api:example:insurance",
+      "client"
     )
-end CommandEngineController
 
 object ClientController:
-  private val fetchMany =
-    Endpoint(Method.GET / "clients")
-      .query(pageParams)
-      .out[JsonApiResponse.Many[ClientState]]
-
-  private val fetchOne =
-    Endpoint(Method.GET / "clients" / string("entityId"))
-      .out[JsonApiResponse.One[ClientState]]
-
-  private val createCommand =
-    Endpoint(Method.POST / "clients" / "commands" / "create")
-      .in[ClientCommand.Create]
-      .out[JsonApiResponse.One[ClientEvent]]
-
-  private val updateCommand =
-    Endpoint(Method.PUT / "clients" / string("entityId") / "commands" / "udpate")
-      .in[ClientCommand.Update]
-      .out[JsonApiResponse.One[ClientEvent]]
-
-  private val disableCommand =
-    Endpoint(Method.PUT / "clients" / string("entityId") / "commands" / "disable")
-      .in[ClientCommand.Disable]
-      .out[JsonApiResponse.One[ClientEvent]]
-
-  private val fetchEventsMany =
-    Endpoint(Method.GET / "clients" / string("entityId") / "events")
-      .query(pageParams)
-      .out[JsonApiResponse.Many[ClientEvent]]
-
-  private val fetchEventsOne =
-    Endpoint(Method.GET / "clients" / string("entityId") / "events" / string("eventId"))
-      .out[JsonApiResponse.One[ClientEvent]]
-
-  private val fetchManyRoute =
-    fetchMany.implement(page =>
-      ZIO.succeed(
-        JsonApiResponse.Many[ClientState](
-          List.empty,
-          JsonApiResponse.Links("https://api.example.org"),
-          meta = JsonApiResponse.Meta(None, None)
-        )
-      )
-    )
-
-  private val createCommandRoute =
-    createCommand.implement(command =>
-      ZIO.succeed(
-        JsonApiResponse.One[ClientEvent](
-          JsonApiResponse.Entity(
-            id = "todo",
-            `type` = "todo",
-            ClientEvent.Created(
-              lastName = command.lastName,
-              firstName = command.firstName,
-              birthDate = command.birthDate,
-              drivingLicenseDate = command.drivingLicenseDate,
-              phoneNumber = command.phoneNumber,
-              email = command.email,
-              address = command.address
-            )
-          ),
-          JsonApiResponse.Links("https://api.example.org")
-        )
-      )
-    )
-
-  val endpoints = List(
-    fetchMany,
-    fetchOne,
-    createCommand,
-    updateCommand,
-    disableCommand,
-    fetchEventsMany,
-    fetchEventsOne
-  )
-  val routes = Routes(fetchManyRoute)
-end ClientController
+  val layer = ZLayer.fromFunction(ClientController.apply)
diff --git a/api/src/lu/foyer/clients/ClientEventRepositoryInMemory.scala b/api/src/lu/foyer/clients/ClientEventRepositoryInMemory.scala
new file mode 100644
index 0000000..c9e0018
--- /dev/null
+++ b/api/src/lu/foyer/clients/ClientEventRepositoryInMemory.scala
@@ -0,0 +1,23 @@
+package lu.foyer
+package clients
+
+import java.util.UUID
+import zio.*
+
+class ClientEventRepositoryInMemory(events: Ref[Map[UUID, Event[ClientEvent]]])
+    extends EventRepository[ClientEvent]
+    with InMemoryRepository[Event[ClientEvent]](events):
+  def fetchOne(entityId: UUID, eventId: UUID): Task[Option[Event[ClientEvent]]] =
+    events.get.map(_.get(eventId))
+  def fetchMany(entityId: UUID, page: Page): Task[Paged[Event[ClientEvent]]] =
+    events.get
+      .map(entities =>
+        val items = entities.values
+          .filter(_.entityId == entityId)
+          .drop(page.number.getOrElse(0) * page.size.getOrElse(50))
+          .take(page.size.getOrElse(50))
+        Paged(items.toList, if page.totals.getOrElse(false) then Some(entities.size) else None)
+      )
+
+object ClientEventRepositoryInMemory:
+  val layer = ZLayer.fromZIO(Ref.make(Map.empty).map(ClientEventRepositoryInMemory(_)))
diff --git a/api/src/lu/foyer/clients/ClientStateRepositoryInMemory.scala b/api/src/lu/foyer/clients/ClientStateRepositoryInMemory.scala
new file mode 100644
index 0000000..f6f5266
--- /dev/null
+++ b/api/src/lu/foyer/clients/ClientStateRepositoryInMemory.scala
@@ -0,0 +1,12 @@
+package lu.foyer
+package clients
+
+import java.util.UUID
+import zio.*
+
+class ClientStateRepositoryInMemory(clients: Ref[Map[UUID, Entity[ClientState]]])
+    extends StateRepository[ClientState]
+    with InMemoryRepository[Entity[ClientState]](clients)
+
+object ClientStateRepositoryInMemory:
+  val layer = ZLayer.fromZIO(Ref.make(Map.empty).map(ClientStateRepositoryInMemory(_)))
diff --git a/build.sc b/build.sc
index f09ce35..a018887 100644
--- a/build.sc
+++ b/build.sc
@@ -1,12 +1,17 @@
 // scalafmt: { runner.dialect = scala213 }
 package build
 import mill._, scalalib._
+import coursier.maven.MavenRepository
+
+val sonatypeSnapshots = Seq(
+  MavenRepository("https://oss.sonatype.org/content/repositories/snapshots")
+)
 
 object Versions {
   val zio        = "2.1.15"
   val zioJson    = "0.7.33"
   val zioSchema  = "1.6.3"
-  val zioHttp    = "3.0.1"
+  val zioHttp    = "3.0.1+97-29d12531-SNAPSHOT"
   val zioPrelude = "1.0.0-RC39"
 }
 
@@ -18,6 +23,9 @@ trait CommonModule extends ScalaModule {
     ivy"dev.zio::zio-schema-derivation:${Versions.zioSchema}",
     ivy"dev.zio::zio-prelude:${Versions.zioPrelude}"
   )
+  def repositoriesTask = Task.Anon {
+    super.repositoriesTask() ++ sonatypeSnapshots
+  }
 }
 
 object model extends CommonModule
diff --git a/core/src/lu/foyer/EventSourcing.scala b/core/src/lu/foyer/EventSourcing.scala
index af9aa0f..4212d79 100644
--- a/core/src/lu/foyer/EventSourcing.scala
+++ b/core/src/lu/foyer/EventSourcing.scala
@@ -2,25 +2,42 @@ package lu.foyer
 
 import zio.*
 import java.util.UUID
+import zio.schema.Schema
 
 final case class Entity[T](entityId: UUID, data: T, version: Long)
 final case class Event[T](entityId: UUID, data: T, eventId: UUID)
 
-trait StateRepository[State] extends Repository[Entity[State], UUID]
-trait EventRepository[State] extends Repository[Event[State], UUID]
+trait StateRepository[Data] extends Repository[Entity[Data], UUID]
+trait EventRepository[Data] extends Repository[Event[Data], UUID]:
+  def fetchOne(entityId: UUID, eventId: UUID): Task[Option[Event[Data]]]
+  def fetchMany(entityId: UUID, page: Page): Task[Paged[Event[Data]]]
 
 trait Reducer[Event, State]:
-  def reduce(event: Event): Option[State]
-  def reduce(state: State, event: Event): Option[State]
+  def fromEmpty: PartialFunction[Event, State]
+  def fromState: PartialFunction[(State, Event), State]
 
-trait CommandHandler[Command, Event, State]:
+  def reduce(event: Event): Option[State] =
+    fromEmpty.lift(event)
+
+  def reduce(state: State, event: Event): Option[State] =
+    fromState.lift((state, event))
+
+trait CommandHandler[+Command, +Event, +State]:
   def name: String
+  def isCreate: Boolean
+  inline def isUpdate: Boolean = !isCreate
+  def commandSchema: Schema[?]
 
-trait CommandHandlerCreate[Command, Event, State] extends CommandHandler[Command, Event, State]:
+trait CommandHandlerCreate[Command: Schema, Event] extends CommandHandler[Command, Event, Nothing]:
   def onCommand(entityId: UUID, command: Command): Task[Event]
+  val isCreate      = true
+  val commandSchema = summon[Schema[Command]]
 
-trait CommandHandlerUpdate[Command, Event, State] extends CommandHandler[Command, Event, State]:
+trait CommandHandlerUpdate[Command: Schema, Event, State]
+    extends CommandHandler[Command, Event, State]:
   def onCommand(entityId: UUID, state: State, command: Command): Task[Event]
+  val isCreate      = false
+  val commandSchema = summon[Schema[Command]]
 
 class CommandEngine[Command, Event, State](
   val handlers: List[CommandHandler[Command, Event, State]],
@@ -28,7 +45,8 @@ class CommandEngine[Command, Event, State](
   val eventRepo: EventRepository[Event],
   val stateRepo: StateRepository[State]):
 
-  def handleCommand(command: Command, name: String, entityId: UUID): Task[(Event, State)] =
+  def handleCommand(command: Command, name: String, entityId: UUID)
+    : Task[(lu.foyer.Event[Event], lu.foyer.Entity[State])] =
     for
       handler <- ZIO
                    .succeed(handlers.find(_.name == name))
@@ -39,13 +57,12 @@ class CommandEngine[Command, Event, State](
         ZIO
           .succeed(newStateOption)
           .someOrFail(new IllegalArgumentException("Reducer cannot resolve state transition"))
-      newEntity <-
-        Random.nextUUID.map(Entity(_, newState, entityOption.map(_.version).getOrElse(1)))
-      _ <- if entityOption.isEmpty then stateRepo.insert(newEntity)
+      newEntity = Entity(entityId, newState, entityOption.map(_.version).getOrElse(1))
+      _ <- if entityOption.isEmpty then stateRepo.insert(newEntity.entityId, newEntity)
            else stateRepo.update(newEntity.entityId, newEntity)
       eventEntity <- Random.nextUUID.map(Event(newEntity.entityId, event, _))
-      _           <- eventRepo.insert(eventEntity)
-    yield (event, newState)
+      _           <- eventRepo.insert(eventEntity.eventId, eventEntity)
+    yield (eventEntity, newEntity)
 
   private def transition(
     command: Command,
@@ -54,21 +71,23 @@ class CommandEngine[Command, Event, State](
     entityOption: Option[Entity[State]],
     handler: CommandHandler[Command, Event, State]
   ): Task[(Event, Option[State])] = (entityOption, handler) match
-    case (None, h: CommandHandlerCreate[Command, Event, State]) =>
-      h.onCommand(entityId, command)
+    case (None, h) if !h.isUpdate =>
+      h.asInstanceOf[CommandHandlerCreate[Command, Event]]
+        .onCommand(entityId, command)
         .map(event => (event, reducer.reduce(event)))
-    case (Some(entity), h: CommandHandlerUpdate[Command, Event, State]) =>
-      h.onCommand(entityId, entity.data, command)
+    case (Some(entity), h) if h.isUpdate =>
+      h.asInstanceOf[CommandHandlerUpdate[Command, Event, State]]
+        .onCommand(entityId, entity.data, command)
         .map(event => (event, reducer.reduce(entity.data, event)))
-    case (Some(_), _: CommandHandlerCreate[Command, Event, State]) =>
+    case (Some(_), h) if !h.isUpdate =>
       ZIO.fail(
         new IllegalArgumentException(s"State already exists when applying create command $name")
       )
-    case (None, _: CommandHandlerUpdate[Command, Event, State]) =>
+    case (None, h) if h.isUpdate =>
       ZIO.fail(new IllegalArgumentException(s"No state found to apply the update command $name"))
     case _ => ZIO.fail(new IllegalArgumentException("Impossible state"))
 end CommandEngine
 
 object CommandEngine:
-  def layer[Command, Event, State](using Tag[Command], Tag[Event], Tag[State]) =
+  def layer[Command: Tag, Event: Tag, State: Tag] =
     ZLayer.fromFunction(CommandEngine[Command, Event, State](_, _, _, _))
diff --git a/core/src/lu/foyer/Repository.scala b/core/src/lu/foyer/Repository.scala
index 9209818..84e132b 100644
--- a/core/src/lu/foyer/Repository.scala
+++ b/core/src/lu/foyer/Repository.scala
@@ -1,13 +1,28 @@
 package lu.foyer
 
 import zio.*
+import zio.schema.*
 import java.util.UUID
 
-final case class Page(number: Int, size: Int, totals: Boolean)
+final case class Page(number: Option[Int], size: Option[Int], totals: Option[Boolean])
+    derives Schema
 final case class Paged[T](items: List[T], totals: Option[Long])
 
 trait Repository[Entity, Id]:
   def fetchOne(id: Id): Task[Option[Entity]]
   def fetchMany(page: Page): Task[Paged[Entity]]
-  def insert(entity: Entity): Task[Unit]
+  def insert(id: Id, entity: Entity): Task[Unit]
   def update(id: Id, entity: Entity): Task[Unit]
+
+trait InMemoryRepository[State](entities: Ref[Map[UUID, State]]) extends Repository[State, UUID]:
+  def fetchOne(id: UUID): Task[Option[State]] = entities.get.map(_.get(id))
+  def fetchMany(page: Page): Task[Paged[State]] = entities.get.map(entities =>
+    val items =
+      entities.values
+        .drop(page.number.getOrElse(0) * page.size.getOrElse(50)).take(page.size.getOrElse(50))
+    Paged(items.toList, if page.totals.getOrElse(false) then Some(entities.size) else None)
+  )
+  def insert(id: UUID, entity: State): Task[Unit] =
+    entities.update(entities => entities.updated(id, entity))
+  def update(id: UUID, entity: State): Task[Unit] =
+    entities.update(entities => entities.updated(id, entity))
diff --git a/core/src/lu/foyer/clients/ClientHandlers.scala b/core/src/lu/foyer/clients/ClientHandlers.scala
new file mode 100644
index 0000000..2e80a41
--- /dev/null
+++ b/core/src/lu/foyer/clients/ClientHandlers.scala
@@ -0,0 +1,54 @@
+package lu.foyer
+package clients
+
+import zio.*
+import java.util.UUID
+
+object ClientHandlers:
+  val layer: ULayer[List[CommandHandler[ClientCommand, ClientEvent, ClientState]]] =
+    ZLayer.succeed(
+      List(
+        CreateHandler,
+        UpdateHandler,
+        DisableHandler
+      )
+    )
+
+object CreateHandler extends CommandHandlerCreate[ClientCommand.Create, ClientEvent.Created]:
+  val name = "create"
+  def onCommand(entityId: UUID, command: ClientCommand.Create): Task[ClientEvent.Created] =
+    ZIO.succeed(
+      ClientEvent.Created(
+        command.lastName,
+        command.firstName,
+        command.birthDate,
+        command.drivingLicenseDate,
+        command.phoneNumber,
+        command.email,
+        command.address
+      )
+    )
+
+object UpdateHandler
+    extends CommandHandlerUpdate[ClientCommand.Update, ClientEvent.Updated, ClientState.Actif]:
+  val name = "update"
+  def onCommand(entityId: UUID, state: ClientState.Actif, command: ClientCommand.Update)
+    : Task[ClientEvent.Updated] =
+    ZIO.succeed(
+      ClientEvent.Updated(
+        command.lastName,
+        command.firstName,
+        command.birthDate,
+        command.drivingLicenseDate,
+        command.phoneNumber,
+        command.email,
+        command.address
+      )
+    )
+
+object DisableHandler
+    extends CommandHandlerUpdate[ClientCommand.Disable, ClientEvent.Disabled, ClientState.Actif]:
+  val name = "disable"
+  def onCommand(entityId: UUID, state: ClientState.Actif, command: ClientCommand.Disable)
+    : Task[ClientEvent.Disabled] =
+    ZIO.succeed(ClientEvent.Disabled(command.reason))
diff --git a/core/src/lu/foyer/clients/ClientReducer.scala b/core/src/lu/foyer/clients/ClientReducer.scala
index 47988f7..aa53dbf 100644
--- a/core/src/lu/foyer/clients/ClientReducer.scala
+++ b/core/src/lu/foyer/clients/ClientReducer.scala
@@ -1,48 +1,16 @@
 package lu.foyer
 package clients
 
-object ClientReducer extends Reducer[ClientEvent, ClientState]:
+import zio.*
 
-  def reduce(event: ClientEvent): Option[ClientState] = event match
-    case e: ClientEvent.Created =>
-      Some(
-        ClientState.Actif(
-          e.lastName,
-          e.firstName,
-          e.birthDate,
-          e.drivingLicenseDate,
-          e.phoneNumber,
-          e.email,
-          e.address
-        )
-      )
-    case _: ClientEvent.Updated  => None
-    case _: ClientEvent.Disabled => None
+class ClientReducer() extends Reducer[ClientEvent, ClientState]:
 
-  def reduce(state: ClientState, event: ClientEvent): Option[ClientState] = (state, event) match
-    case (s: ClientState.Actif, e: ClientEvent.Updated) =>
-      Some(
-        ClientState.Actif(
-          e.lastName.getOrElse(s.lastName),
-          e.firstName.getOrElse(s.firstName),
-          e.birthDate.getOrElse(s.birthDate),
-          e.drivingLicenseDate.orElse(s.drivingLicenseDate),
-          e.phoneNumber.orElse(s.phoneNumber),
-          e.email.orElse(s.email),
-          e.address.orElse(s.address)
-        )
-      )
-    case (s: ClientState.Actif, _: ClientEvent.Disabled) =>
-      Some(
-        ClientState.Inactif(
-          s.lastName,
-          s.firstName,
-          s.birthDate,
-          s.drivingLicenseDate,
-          s.phoneNumber,
-          s.email,
-          s.address
-        )
-      )
-    case _ => None
-end ClientReducer
+  override val fromEmpty =
+    case e: ClientEvent.Created => ClientState.create(e)
+
+  override val fromState =
+    case (s: ClientState.Actif, e: ClientEvent.Updated)  => s.update(e)
+    case (s: ClientState.Actif, e: ClientEvent.Disabled) => s.disable(e)
+
+object ClientReducer:
+  val layer: ULayer[Reducer[ClientEvent, ClientState]] = ZLayer.succeed(ClientReducer())
diff --git a/core/src/lu/foyer/clients/ClientState.scala b/core/src/lu/foyer/clients/ClientState.scala
index 5f2efe3..3ee8363 100644
--- a/core/src/lu/foyer/clients/ClientState.scala
+++ b/core/src/lu/foyer/clients/ClientState.scala
@@ -24,3 +24,37 @@ enum ClientState derives Schema:
     phoneNumber: Option[PhoneNumberInput],
     email: Option[Email],
     address: Option[Address])
+
+object ClientState:
+  def create(event: ClientEvent.Created) =
+    ClientState.Actif(
+      event.lastName,
+      event.firstName,
+      event.birthDate,
+      event.drivingLicenseDate,
+      event.phoneNumber,
+      event.email,
+      event.address
+    )
+
+extension (s: ClientState.Actif)
+  def update(e: ClientEvent.Updated) =
+    ClientState.Actif(
+      e.lastName.getOrElse(s.lastName),
+      e.firstName.getOrElse(s.firstName),
+      e.birthDate.getOrElse(s.birthDate),
+      e.drivingLicenseDate.orElse(s.drivingLicenseDate),
+      e.phoneNumber.orElse(s.phoneNumber),
+      e.email.orElse(s.email),
+      e.address.orElse(s.address)
+    )
+  def disable(e: ClientEvent.Disabled) =
+    ClientState.Inactif(
+      s.lastName,
+      s.firstName,
+      s.birthDate,
+      s.drivingLicenseDate,
+      s.phoneNumber,
+      s.email,
+      s.address
+    )
diff --git a/flake.nix b/flake.nix
index 4975e23..8c06303 100644
--- a/flake.nix
+++ b/flake.nix
@@ -46,7 +46,7 @@
 
                 services = {
                   kafka.enable = true;
-                  mongodb.enable = true;
+                  # mongodb.enable = true;
                 };
 
               }
diff --git a/model/src/lu/foyer/clients/Client.scala b/model/src/lu/foyer/clients/Client.scala
index a4e8ed2..4328d24 100644
--- a/model/src/lu/foyer/clients/Client.scala
+++ b/model/src/lu/foyer/clients/Client.scala
@@ -33,7 +33,6 @@ case class Client(
   address: Address)
     derives Schema
 
-// TODO validate using libphonenumber
 case class PhoneNumber(
   country: Country,
   nationalNumber: NationalNumber,