feat(scalasdk): codegen for ValueEntityHandler.

codegen/core/src/main/scala/com/lightbend/akkasls/codegen/ModelBuilder.scala

@@ -77,7 +77,7 @@ object ModelBuilder {
       state: State)
       extends Entity(fqn, entityType) {
     val abstractEntityName = "Abstract" + fqn.name
-
+    val handlerName = fqn.name + "Handler"
   }
 
   /**

codegen/scala-gen/src/main/scala/com/akkaserverless/codegen/scalasdk/impl/ValueEntitySourceGenerator.scala

@@ -41,7 +41,8 @@ object ValueEntitySourceGenerator {
     generatedSources += File(
       s"$packagePath/${valueEntity.abstractEntityName}.scala",
       abstractEntity(valueEntity, service))
-    //FIXME add Handler and Provider
+    generatedSources += File(s"$packagePath/${valueEntity.handlerName}.scala", handler(valueEntity, service))
+    //FIXME add Provider
 
     generatedSources.result()
   }
@@ -86,6 +87,54 @@ object ValueEntitySourceGenerator {
         |""".stripMargin
   }
 
+  private[codegen] def handler(valueEntity: ModelBuilder.ValueEntity, service: ModelBuilder.EntityService): String = {
+    val stateType = valueEntity.state.fqn.name
+    val packageName = valueEntity.fqn.parent.scalaPackage
+    val valueEntityName = valueEntity.fqn.name
+    implicit val imports =
+      generateImports(
+        Seq(valueEntity.state.fqn) ++
+        service.commands.map(_.inputType) ++
+        service.commands.map(_.outputType),
+        valueEntity.fqn.parent.scalaPackage,
+        otherImports = Seq(
+          "com.akkaserverless.scalasdk.valueentity.CommandContext",
+          "com.akkaserverless.scalasdk.valueentity.ValueEntity",
+          "com.akkaserverless.scalasdk.impl.valueentity.ValueEntityHandler",
+          "com.akkaserverless.scalasdk.impl.valueentity.ValueEntityHandler.CommandHandlerNotFound"),
+        packageImports = Seq(service.fqn.parent.scalaPackage),
+        semi = false)
+
+    val commandCases = service.commands
+      .map { cmd =>
+        val methodName = cmd.name
+        val inputType = typeName(cmd.inputType)
+        s"""|case "$methodName" =>
+            |  entity.${lowerFirst(methodName)}(state, command.asInstanceOf[$inputType])
+            |""".stripMargin
+      }
+
+    s"""|package $packageName
+        |
+        |$imports
+        |
+        |/**
+        | * A value entity handler that is the glue between the Protobuf service <code>CounterService</code>
+        | * and the command handler methods in the <code>Counter</code> class.
+        | */
+        |class ${valueEntityName}Handler(entity: ${valueEntityName}) extends ValueEntityHandler[$stateType, ${valueEntityName}](entity) {
+        |  def handleCommand(commandName: String, state: $stateType, command: Any, context: CommandContext): ValueEntity.Effect[_] = {
+        |    commandName match {
+        |      ${Format.indent(commandCases, 6)}
+        |
+        |      case _ =>
+        |        throw new ValueEntityHandler.CommandHandlerNotFound(commandName)
+        |    }
+        |  }
+        |}
+        |""".stripMargin
+  }
+
   def generateImplementationSkeleton(
       valueEntity: ModelBuilder.ValueEntity,
       service: ModelBuilder.EntityService): File = {

codegen/scala-gen/src/test/scala/com/akkaserverless/codegen/scalasdk/ValueEntitySourceGeneratorSuite.scala

@@ -77,4 +77,38 @@ class ValueEntitySourceGeneratorSuite extends munit.FunSuite {
           |""".stripMargin)
   }
 
+  test("it can generate a value entity handler implementation") {
+    val str = handler(testData.valueEntity(domainParent), testData.simpleEntityService(apiParent))
+    assertNoDiff(
+      str,
+      s"""package com.example.service.domain
+          |
+          |import com.akkaserverless.scalasdk.impl.valueentity.ValueEntityHandler
+          |import com.akkaserverless.scalasdk.impl.valueentity.ValueEntityHandler.CommandHandlerNotFound
+          |import com.akkaserverless.scalasdk.valueentity.CommandContext
+          |import com.akkaserverless.scalasdk.valueentity.ValueEntity
+          |import com.example.service
+          |import com.external.Empty
+          |
+          |/**
+          | * A value entity handler that is the glue between the Protobuf service <code>CounterService</code>
+          | * and the command handler methods in the <code>Counter</code> class.
+          | */
+          |class MyValueEntityHandler(entity: MyValueEntity) extends ValueEntityHandler[MyState, MyValueEntity](entity) {
+          |  def handleCommand(commandName: String, state: MyState, command: Any, context: CommandContext): ValueEntity.Effect[_] = {
+          |    commandName match {
+          |      case "Set" =>
+          |        entity.set(state, command.asInstanceOf[service.SetValue])
+          |
+          |      case "Get" =>
+          |        entity.get(state, command.asInstanceOf[service.GetValue])
+          |
+          |      case _ =>
+          |        throw new ValueEntityHandler.CommandHandlerNotFound(commandName)
+          |    }
+          |  }
+          |}
+          |""".stripMargin)
+  }
+
 }

sdk/scala-sdk/src/main/scala/com/akkaserverless/scalasdk/impl/valueentity/ValueEntityHandler.scala

@@ -19,6 +19,10 @@ package com.akkaserverless.scalasdk.impl.valueentity
 import com.akkaserverless.scalasdk.valueentity.CommandContext
 import com.akkaserverless.scalasdk.valueentity.ValueEntity
 
+object ValueEntityHandler {
+  final case class CommandHandlerNotFound(commandName: String) extends RuntimeException
+}
+
 abstract class ValueEntityHandler[S, E <: ValueEntity[S]](val entity: E) {
   def handleCommand(commandName: String, state: S, command: Any, context: CommandContext): ValueEntity.Effect[_]
 }