package controllers

import javax.inject.{Inject,Singleton}

import play.api.{Environment,Mode}
import play.api.mvc.{Controller,Action}

// Import required for injection
import play.api.libs.ws.WSClient
import scala.concurrent.ExecutionContext

/**
 * This controller creates an `Action` to handle HTTP requests to the
 * application's home page.
 */
@Singleton
class HomeController @Inject()(ws: WSClient, environment: Environment)(implicit ec: ExecutionContext) extends Controller {

  def index = Assets.versioned(path="/public/dist", "index.html")

  def dist(file: String) = environment.mode match {
    case Mode.Dev => Action.async {
      ws.url("http://localhost:4200/dist/" + file).get().map { response =>
        Ok(response.body)
      }
    }
    // If Production, use build files.
    case Mode.Prod => Assets.versioned(path="/public/dist", file)
  }

}

<...>

/* ================================= NG BUILD ================================== */

val frontEndProjectName = "frontend"
val backEndProjectName = "backend"
val distDirectory = ".." + backEndProjectName + "public/dist"

// Starts: angularCLI build task
val frontendDirectory = baseDirectory {_ /".."/frontEndProjectName}

val ng = sys.props("os.name").toLowerCase match {
  case os if os.contains("win") => "cmd /c ng"
  case _ => "ng"
}

val params = sys.props("os.name").toLowerCase match {
  case os if os.contains("win") => " build --deploy-url /dist --output-path ..\\backend\\public\\dist --progress "
  case _ => " build --deploy-url /dist --output-path ../backend/public/dist --progress "
}

val ngBuild = taskKey[Unit]("ng build task.")
ngBuild := { Process( ng + params , frontendDirectory.value) ! }
(packageBin in Universal) <<= (packageBin in Universal) dependsOn ngBuild
// Ends.