Monadic-ScalaFX-Demo/src/main/scala/nova/monadic_sfx/util/SynchedObject.scala

package nova.monadic_sfx.util

import monix.bio.Task
import monix.bio.UIO
import monix.catnap.MVar

/**
  * Synchronization wrapper for a mutable object
  *
  * @param obj the mutable object
  * @param lock lock for synchronization
  */
class SynchedObject[A](obj: A, lock: MLock) {

  def modify(f: A => Task[Unit]): Task[Unit] =
    lock.greenLight(f(obj))

  def get: Task[A] = lock.greenLight(Task(obj))
}

object SynchedObject {
  def apply[A](obj: A) =
    MVar[Task]
      .of(())
      .map(m => new MLock(m))
      .flatMap(lock => Task(new SynchedObject(obj, lock)))
}

final class MLock(mvar: MVar[Task, Unit]) {
  def acquire: Task[Unit] =
    mvar.take

  def release: Task[Unit] =
    mvar.put(())

  def greenLight[A](fa: Task[A]): Task[A] =
    for {
      _ <- acquire
      a <- fa.doOnCancel(
        release.onErrorHandleWith(ex => UIO(println(ex.getMessage())))
      )
      _ <- release
    } yield a
}