Feature.swift

/*
 The following feature is 100% pure Swift code. It compiles for a multitude of platforms,
 include iOS, macOS, Linux, Windows, Wasm, and more. It encapsulates all of the logic
 and behavior for the feature so that the view can concentrate on just the UI by reading
 state from the model and invoking methods on the model.
*/

import Dependencies
import FactClient
import Perception
import SwiftNavigation

@MainActor
@Perceptible
public class CounterModel: HashableObject {
  @PerceptionIgnored
  @Dependency(FactClient.self) var factClient
  @PerceptionIgnored
  @Dependency(\.continuousClock) var clock

  public var alert: AlertState<Never>? {
    didSet {
      if alert == nil, shouldResumeTimerAfterFactDismissal {
        shouldResumeTimerAfterFactDismissal = false
        startTimer()
      }
    }
  }
  public var count = 0
  public var factIsLoading = false
  private var timerTask: Task<Void, Error>?
  private var shouldResumeTimerAfterFactDismissal = false

  public var isTimerRunning: Bool { timerTask != nil }

  public init() {}

  public func incrementButtonTapped() {
    count += 1
    alert = nil
  }

  public func decrementButtonTapped() {
    count -= 1
    alert = nil
  }

  public func factButtonTapped() async {
    alert = nil
    factIsLoading = true
    defer { factIsLoading = false }
    shouldResumeTimerAfterFactDismissal = isTimerRunning
    stopTimer()

    do {
      try await Task.sleep(for: .seconds(1))
      let fact = try await factClient.fetch(count)
      alert = AlertState {
        TextState("Fact")
      } message: {
        TextState(fact)
      }
    } catch {
    }
  }

  public func toggleTimerButtonTapped() {
    if isTimerRunning {
      stopTimer()
    } else {
      startTimer()
    }
  }

  private func startTimer() {
    timerTask?.cancel()
    timerTask = Task {
      for await _ in clock.timer(interval: .seconds(1)) {
        count += 1
      }
    }
  }

  private func stopTimer() {
    timerTask?.cancel()
    timerTask = nil
  }
}