swift-composable-architecture-mirror/Sources/ComposableArchitecture/SwiftUI/Alert.swift

import SwiftUI

/// A data type that describes the state of an alert that can be shown to the user. The `Action`
/// generic is the type of actions that can be sent from tapping on a button in the alert.
///
/// This type can be used in your application's state in order to control the presentation or
/// dismissal of alerts. It is preferable to use this API instead of the default SwiftUI API
/// for alerts because SwiftUI uses 2-way bindings in order to control the showing and dismissal
/// of alerts, and that does not play nicely with the Composable Architecture. The library requires
/// that all state mutations happen by sending an action so that a reducer can handle that logic,
/// which greatly simplifies how data flows through your application, and gives you instant
/// testability on all parts of your application.
///
/// To use this API, you model all the alert actions in your domain's action enum:
///
/// ```swift
/// enum AppAction: Equatable {
///   case cancelTapped
///   case confirmTapped
///   case deleteTapped
///
///   // Your other actions
/// }
/// ```
///
/// And you model the state for showing the alert in your domain's state, and it can start off
/// `nil`:
///
/// ```swift
/// struct AppState: Equatable {
///   var alert: AlertState<AppAction>?
///
///   // Your other state
/// }
/// ```
///
/// Then, in the reducer you can construct an ``AlertState`` value to represent the alert you want
/// to show to the user:
///
/// ```swift
/// let appReducer = Reducer<AppState, AppAction, AppEnvironment> { state, action, env in
///   switch action
///     case .cancelTapped:
///       state.alert = nil
///       return .none
///
///     case .confirmTapped:
///       state.alert = nil
///       // Do deletion logic...
///
///     case .deleteTapped:
///       state.alert = .init(
///         title: TextState("Delete"),
///         message: TextState("Are you sure you want to delete this? It cannot be undone."),
///         primaryButton: .default(TextState("Confirm"), action: .send(.confirmTapped)),
///         secondaryButton: .cancel()
///       )
///     return .none
///   }
/// }
/// ```
///
/// And then, in your view you can use the `.alert(_:send:dismiss:)` method on `View` in order
/// to present the alert in a way that works best with the Composable Architecture:
///
/// ```swift
/// Button("Delete") { viewStore.send(.deleteTapped) }
///   .alert(
///     self.store.scope(state: \.alert),
///     dismiss: .cancelTapped
///   )
/// ```
///
/// This makes your reducer in complete control of when the alert is shown or dismissed, and makes
/// it so that any choice made in the alert is automatically fed back into the reducer so that you
/// can handle its logic.
///
/// Even better, you can instantly write tests that your alert behavior works as expected:
///
/// ```swift
/// let store = TestStore(
///   initialState: AppState(),
///   reducer: appReducer,
///   environment: .mock
/// )
///
/// store.send(.deleteTapped) {
///   $0.alert = .init(
///     title: TextState("Delete"),
///     message: TextState("Are you sure you want to delete this? It cannot be undone."),
///     primaryButton: .default(TextState("Confirm"), action: .send(.confirmTapped)),
///     secondaryButton: .cancel(action: .send(.cancelTapped))
///   )
/// }
/// store.send(.deleteTapped) {
///   $0.alert = nil
///   // Also verify that delete logic executed correctly
/// }
/// ```
///
public struct AlertState<Action> {
  public let id = UUID()
  public var message: TextState?
  public var primaryButton: Button?
  public var secondaryButton: Button?
  public var title: TextState

  public init(
    title: TextState,
    message: TextState? = nil,
    dismissButton: Button? = nil
  ) {
    self.title = title
    self.message = message
    self.primaryButton = dismissButton
  }

  public init(
    title: TextState,
    message: TextState? = nil,
    primaryButton: Button,
    secondaryButton: Button
  ) {
    self.title = title
    self.message = message
    self.primaryButton = primaryButton
    self.secondaryButton = secondaryButton
  }

  public struct Button {
    public var action: ButtonAction?
    public var type: ButtonType

    public static func cancel(
      _ label: TextState,
      action: ButtonAction? = nil
    ) -> Self {
      Self(action: action, type: .cancel(label: label))
    }

    public static func cancel(
      action: ButtonAction? = nil
    ) -> Self {
      Self(action: action, type: .cancel(label: nil))
    }

    public static func `default`(
      _ label: TextState,
      action: ButtonAction? = nil
    ) -> Self {
      Self(action: action, type: .default(label: label))
    }

    public static func destructive(
      _ label: TextState,
      action: ButtonAction? = nil
    ) -> Self {
      Self(action: action, type: .destructive(label: label))
    }
  }

  public struct ButtonAction {
    let type: ActionType

    public static func send(_ action: Action) -> Self {
      .init(type: .send(action))
    }

    public static func send(_ action: Action, animation: Animation?) -> Self {
      .init(type: .animatedSend(action, animation: animation))
    }

    enum ActionType {
      case send(Action)
      case animatedSend(Action, animation: Animation?)
    }
  }

  public enum ButtonType {
    case cancel(label: TextState?)
    case `default`(label: TextState)
    case destructive(label: TextState)
  }
}

extension View {
  /// Displays an alert when then store's state becomes non-`nil`, and dismisses it when it becomes
  /// `nil`.
  ///
  /// - Parameters:
  ///   - store: A store that describes if the alert is shown or dismissed.
  ///   - dismissal: An action to send when the alert is dismissed through non-user actions, such
  ///     as when an alert is automatically dismissed by the system. Use this action to `nil` out
  ///     the associated alert state.
  public func alert<Action>(
    _ store: Store<AlertState<Action>?, Action>,
    dismiss: Action
  ) -> some View {

    WithViewStore(store, removeDuplicates: { $0?.id == $1?.id }) { viewStore in
      self.alert(item: viewStore.binding(send: dismiss)) { state in
        state.toSwiftUI(send: viewStore.send)
      }
    }
  }
}

extension AlertState: CustomDebugOutputConvertible {
  public var debugOutput: String {
    let fields = (
      title: self.title,
      message: self.message,
      primaryButton: self.primaryButton,
      secondaryButton: self.secondaryButton
    )
    return "\(Self.self)\(ComposableArchitecture.debugOutput(fields))"
  }
}

extension AlertState: Equatable where Action: Equatable {
  public static func == (lhs: Self, rhs: Self) -> Bool {
    lhs.title == rhs.title
      && lhs.message == rhs.message
      && lhs.primaryButton == rhs.primaryButton
      && lhs.secondaryButton == rhs.secondaryButton
  }
}

extension AlertState: Hashable where Action: Hashable {
  public func hash(into hasher: inout Hasher) {
    hasher.combine(self.title)
    hasher.combine(self.message)
    hasher.combine(self.primaryButton)
    hasher.combine(self.secondaryButton)
  }
}

extension AlertState: Identifiable {}

extension AlertState.ButtonAction: Equatable where Action: Equatable {}
extension AlertState.ButtonAction.ActionType: Equatable where Action: Equatable {}
extension AlertState.ButtonType: Equatable {}
extension AlertState.Button: Equatable where Action: Equatable {}

extension AlertState.ButtonAction: Hashable where Action: Hashable {}
extension AlertState.ButtonAction.ActionType: Hashable where Action: Hashable {
  func hash(into hasher: inout Hasher) {
    switch self {
    case let .send(action), let .animatedSend(action, animation: _):
      hasher.combine(action)
    }
  }
}
extension AlertState.ButtonType: Hashable {}
extension AlertState.Button: Hashable where Action: Hashable {
  public func hash(into hasher: inout Hasher) {
    hasher.combine(self.action)
    hasher.combine(self.type)
  }
}

extension AlertState.Button {
  func toSwiftUI(send: @escaping (Action) -> Void) -> SwiftUI.Alert.Button {
    let action = {
      switch self.action?.type {
      case .none:
        return
      case let .some(.send(action)):
        send(action)
      case let .some(.animatedSend(action, animation: animation)):
        withAnimation(animation) { send(action) }
      }
    }
    switch self.type {
    case let .cancel(.some(label)):
      return .cancel(Text(label), action: action)
    case .cancel(.none):
      return .cancel(action)
    case let .default(label):
      return .default(Text(label), action: action)
    case let .destructive(label):
      return .destructive(Text(label), action: action)
    }
  }
}

extension AlertState {
  fileprivate func toSwiftUI(send: @escaping (Action) -> Void) -> SwiftUI.Alert {
    if let primaryButton = self.primaryButton, let secondaryButton = self.secondaryButton {
      return SwiftUI.Alert(
        title: Text(self.title),
        message: self.message.map { Text($0) },
        primaryButton: primaryButton.toSwiftUI(send: send),
        secondaryButton: secondaryButton.toSwiftUI(send: send)
      )
    } else {
      return SwiftUI.Alert(
        title: Text(self.title),
        message: self.message.map { Text($0) },
        dismissButton: self.primaryButton?.toSwiftUI(send: send)
      )
    }
  }
}