export class BackPressureStrategy<in out A> implements PubSub.Strategy<A> {
  publishers: MutableList.MutableList<
    readonly [A, Deferred.Deferred<boolean>, boolean]
  > = MutableList.make()

  get shutdown(): Effect.Effect<void> {
    return Effect.withFiber((fiber) =>
      Effect.forEach(
        MutableList.takeAll(this.publishers),
        ([_, deferred, last]) => last ? Deferred.interruptWith(deferred, fiber.id) : Effect.void,
        { concurrency: "unbounded", discard: true }
      )
    )
  }

  handleSurplus(
    pubsub: PubSub.Atomic<A>,
    subscribers: PubSub.Subscribers<A>,
    elements: Iterable<A>,
    isShutdown: MutableRef.MutableRef<boolean>
  ): Effect.Effect<boolean> {
    return Effect.suspend(() => {
      const deferred = Deferred.makeUnsafe<boolean>()
      this.offerUnsafe(elements, deferred)
      this.onPubSubEmptySpaceUnsafe(pubsub, subscribers)
      this.completeSubscribersUnsafe(pubsub, subscribers)
      return (MutableRef.get(isShutdown) ? Effect.interrupt : Deferred.await(deferred)).pipe(
        Effect.onInterrupt(() => {
          this.removeUnsafe(deferred)
          return Effect.void
        })
      )
    })
  }

  onPubSubEmptySpaceUnsafe(
    pubsub: PubSub.Atomic<A>,
    subscribers: PubSub.Subscribers<A>
  ): void {
    let keepPolling = true
    while (keepPolling && !pubsub.isFull()) {
      const publisher = MutableList.take(this.publishers)
      if (publisher === MutableList.Empty) {
        keepPolling = false
      } else {
        const [value, deferred] = publisher
        const published = pubsub.publish(value)
        if (published && publisher[2]) {
          Deferred.doneUnsafe(deferred, Exit.succeed(true))
        } else if (!published) {
          MutableList.prepend(this.publishers, publisher)
        }
        this.completeSubscribersUnsafe(pubsub, subscribers)
      }
    }
  }

  completePollersUnsafe(
    pubsub: PubSub.Atomic<A>,
    subscribers: PubSub.Subscribers<A>,
    subscription: PubSub.BackingSubscription<A>,
    pollers: MutableList.MutableList<Deferred.Deferred<A>>
  ): void {
    return strategyCompletePollersUnsafe(this, pubsub, subscribers, subscription, pollers)
  }

  completeSubscribersUnsafe(pubsub: PubSub.Atomic<A>, subscribers: PubSub.Subscribers<A>): void {
    return strategyCompleteSubscribersUnsafe(this, pubsub, subscribers)
  }

  private offerUnsafe(elements: Iterable<A>, deferred: Deferred.Deferred<boolean>): void {
    const iterator = elements[Symbol.iterator]()
    let next: IteratorResult<A> = iterator.next()
    if (!next.done) {
      // oxlint-disable-next-line no-constant-condition
      while (1) {
        const value = next.value
        next = iterator.next()
        if (next.done) {
          MutableList.append(this.publishers, [value, deferred, true])
          break
        }
        MutableList.append(this.publishers, [value, deferred, false])
      }
    }
  }

  removeUnsafe(deferred: Deferred.Deferred<boolean>): void {
    MutableList.filter(this.publishers, ([_, d]) => d !== deferred)
  }
}