Type safe message router/broker

CustomerMessageBroker.scala

import cats.implicits.*
import cats.Id
import scala.collection.mutable.ListBuffer
import fs2.Stream

// The message broking interface
trait MessageBroker[F[_], Router[_]]:
  def push[MsgKey: ValueOf](value: Router[MsgKey]): F[Unit]
  def subscribe[MsgKey: ValueOf]: Stream[F, Router[MsgKey]]

// =========================================================================
/** Example of usage.
  * Contains 2 message types: 
  *   "order" -> OrderRecord, 
  *   "person" -> PersonRecord
  */
case class OrderRecord(qty: Int = 100, price: Double = 5.0)
case class PersonRecord(name: String = "David")

type MsgKeyOrder  = "order"
type MsgKeyPerson = "person"

/// Type based mssage payload router
type CustomerMsgRouter[MsgKey] = MsgKey match
  case MsgKeyOrder  => OrderRecord
  case MsgKeyPerson => PersonRecord

/// In memory example
object CustomerMessageBroker {
  def apply(): MessageBroker[Id, CustomerMsgRouter] = new MessageBroker[Id, CustomerMsgRouter] {
    // handle all the grunt work.
    private val personBuffer = ListBuffer[PersonRecord]()
    private val orderBuffer  = ListBuffer[OrderRecord]()

    private def getRoutedBuffer[MsgKey: ValueOf]: ListBuffer[CustomerMsgRouter[MsgKey]] = {
      val msgType = valueOf[MsgKey]
      msgType match
        case "order"  => orderBuffer.asInstanceOf[ListBuffer[CustomerMsgRouter[MsgKey]]]
        case "person" => personBuffer.asInstanceOf[ListBuffer[CustomerMsgRouter[MsgKey]]]
    }

    def push[MsgKey: ValueOf](value: CustomerMsgRouter[MsgKey]): Id[Unit] = {
      val buffer = getRoutedBuffer[MsgKey]
      buffer.addOne(value)
    }

    def subscribe[MsgKey: ValueOf]: Stream[Id, CustomerMsgRouter[MsgKey]] = {
      val buffer = getRoutedBuffer[MsgKey]
      Stream.emits(buffer.toList)
    }
  }
}

@main def hello: Unit = {
  val broker = CustomerMessageBroker()

  broker.push[MsgKeyPerson](PersonRecord())
  broker.push[MsgKeyOrder](OrderRecord())
  
  // broker.push[MsgKeyPerson](OrderRecord()) // Compiler Error!!!

  println(s"Orders: ${broker.subscribe[MsgKeyOrder].compile.toList}")
  println(s"Persons: ${broker.subscribe[MsgKeyPerson].compile.toList}")
  
  // Outputs:
  //   Orders: List(OrderRecord(100,5.0))
  //   Persons: List(PersonRecord(David))
}