swift-composable-architecture-mirror/Examples/CaseStudies/UIKitCaseStudies/CounterViewController.swift

import Combine
import ComposableArchitecture
import SwiftUI
import UIKit

struct CounterState: Equatable, Identifiable {
  let id = UUID()
  var count = 0
}

enum CounterAction: Equatable {
  case decrementButtonTapped
  case incrementButtonTapped
}

struct CounterEnvironment {}

let counterReducer = Reducer<CounterState, CounterAction, CounterEnvironment> { state, action, _ in
  switch action {
  case .decrementButtonTapped:
    state.count -= 1
    return .none
  case .incrementButtonTapped:
    state.count += 1
    return .none
  }
}

final class CounterViewController: UIViewController {
  let viewStore: ViewStore<CounterState, CounterAction>
  private var cancellables: Set<AnyCancellable> = []

  init(store: Store<CounterState, CounterAction>) {
    self.viewStore = ViewStore(store)
    super.init(nibName: nil, bundle: nil)
  }

  required init?(coder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  override func viewDidLoad() {
    super.viewDidLoad()

    self.view.backgroundColor = .systemBackground

    let decrementButton = UIButton(type: .system)
    decrementButton.addTarget(self, action: #selector(decrementButtonTapped), for: .touchUpInside)
    decrementButton.setTitle("−", for: .normal)

    let countLabel = UILabel()
    countLabel.font = .monospacedDigitSystemFont(ofSize: 17, weight: .regular)

    let incrementButton = UIButton(type: .system)
    incrementButton.addTarget(self, action: #selector(incrementButtonTapped), for: .touchUpInside)
    incrementButton.setTitle("+", for: .normal)

    let rootStackView = UIStackView(arrangedSubviews: [
      decrementButton,
      countLabel,
      incrementButton,
    ])
    rootStackView.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(rootStackView)

    NSLayoutConstraint.activate([
      rootStackView.centerXAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.centerXAnchor),
      rootStackView.centerYAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.centerYAnchor),
    ])

    self.viewStore.publisher
      .map { "\($0.count)" }
      .assign(to: \.text, on: countLabel)
      .store(in: &self.cancellables)
  }

  @objc func decrementButtonTapped() {
    self.viewStore.send(.decrementButtonTapped)
  }

  @objc func incrementButtonTapped() {
    self.viewStore.send(.incrementButtonTapped)
  }
}

struct CounterViewController_Previews: PreviewProvider {
  static var previews: some View {
    let vc = CounterViewController(
      store: Store(
        initialState: CounterState(),
        reducer: counterReducer,
        environment: CounterEnvironment()
      )
    )
    return UIViewRepresented(makeUIView: { _ in vc.view })
  }
}