swift-composable-architecture-mirror/Sources/ComposableArchitecture/Effects/Throttling.swift

import Combine
import Dispatch

extension Effect {
  /// Throttles an effect so that it only publishes one output per given interval.
  ///
  /// - Parameters:
  ///   - id: The effect's identifier.
  ///   - interval: The interval at which to find and emit the most recent element, expressed in
  ///     the time system of the scheduler.
  ///   - scheduler: The scheduler you want to deliver the throttled output to.
  ///   - latest: A boolean value that indicates whether to publish the most recent element. If
  ///     `false`, the publisher emits the first element received during the interval.
  /// - Returns: An effect that emits either the most-recent or first element received during the
  ///   specified interval.
  public func throttle<S>(
    id: AnyHashable,
    for interval: S.SchedulerTimeType.Stride,
    scheduler: S,
    latest: Bool
  ) -> Effect where S: Scheduler {
    self.receive(on: scheduler)
      .flatMap { value -> AnyPublisher<Output, Failure> in
        throttleLock.lock()
        defer { throttleLock.unlock() }

        guard let throttleTime = throttleTimes[id] as! S.SchedulerTimeType? else {
          throttleTimes[id] = scheduler.now
          throttleValues[id] = nil
          return Just(value).setFailureType(to: Failure.self).eraseToAnyPublisher()
        }

        let value = latest ? value : (throttleValues[id] as! Output? ?? value)
        throttleValues[id] = value

        guard throttleTime.distance(to: scheduler.now) < interval else {
          throttleTimes[id] = scheduler.now
          throttleValues[id] = nil
          return Just(value).setFailureType(to: Failure.self).eraseToAnyPublisher()
        }

        return Just(value)
          .delay(
            for: scheduler.now.distance(to: throttleTime.advanced(by: interval)),
            scheduler: scheduler
          )
          .handleEvents(
            receiveOutput: { _ in
              throttleLock.sync {
                throttleTimes[id] = scheduler.now
                throttleValues[id] = nil
              }
            }
          )
          .setFailureType(to: Failure.self)
          .eraseToAnyPublisher()
      }
      .eraseToEffect()
      .cancellable(id: id, cancelInFlight: true)
  }

  /// Throttles an effect so that it only publishes one output per given interval.
  ///
  /// A convenience for calling ``Effect/throttle(id:for:scheduler:latest:)-5jfpx`` with a static
  /// type as the effect's unique identifier.
  ///
  /// - Parameters:
  ///   - id: The effect's identifier.
  ///   - interval: The interval at which to find and emit the most recent element, expressed in
  ///     the time system of the scheduler.
  ///   - scheduler: The scheduler you want to deliver the throttled output to.
  ///   - latest: A boolean value that indicates whether to publish the most recent element. If
  ///     `false`, the publisher emits the first element received during the interval.
  /// - Returns: An effect that emits either the most-recent or first element received during the
  ///   specified interval.
  public func throttle<S>(
    id: Any.Type,
    for interval: S.SchedulerTimeType.Stride,
    scheduler: S,
    latest: Bool
  ) -> Effect where S: Scheduler {
    self.throttle(id: ObjectIdentifier(id), for: interval, scheduler: scheduler, latest: latest)
  }
}

var throttleTimes: [AnyHashable: Any] = [:]
var throttleValues: [AnyHashable: Any] = [:]
let throttleLock = NSRecursiveLock()