Merge pull request #13 from Lickability/kpa/testing-composibility-sha…

…red-state-and-viewstore

Shared state composable ViewStore example

Example/Photos/With Stores/Banner Feature/Banner.swift

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+//
+//  Banner.swift
+//  ViewStore
+//
+//  Created by Kenneth Ackerson on 4/11/23.
+//
+
+import Foundation
+
+/// Container for text intended to be displayed at the top of a screen.
+struct Banner {
+
+    /// The text to be displayed.
+    let title: String
+}

Example/Photos/With Stores/Banner Feature/BannerDataStore.swift

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+//
+//  BannerDataStore.swift
+//  ViewStore
+//
+//  Created by Kenneth Ackerson on 4/3/23.
+//
+
+import Foundation
+import Combine
+
+typealias BannerDataStoreType = Store<BannerDataStore.State, BannerDataStore.Action>
+
+/// A `Store` that is responsible for being the source of truth for a `Banner`. This includes updating locally and remotely. Not meant to be used to drive a `View`, but rather meant to be composed into other `Store`s.
+final class BannerDataStore: Store {
+
+    // MARK: - Store
+
+    struct State {
+
+        /// Initial state of the banner data store.
+        static let initial = State(banner: .init(title: "Banner"), networkState: .notStarted)
+
+        /// The source of truth of the banner model object.
+        let banner: Banner
+
+        /// Networking state of the request to upload a new banner model to the server.
+        let networkState: MockBannerNetworkStateController.NetworkState
+    }
+
+    enum Action {
+        /// Changes the local copy of the banner model synchronously.
+        case updateBannerLocally(Banner)
+
+        /// Sends the banner to the server and then updates the model locally if it was successful.
+        case uploadBanner(Banner)
+
+        /// Clears the underlying networking state back to `notStarted`.
+        case clearNetworkingState
+    }
+
+    @Published var state: State = BannerDataStore.State.initial
+
+    var publishedState: AnyPublisher<State, Never> {
+        $state.eraseToAnyPublisher()
+    }
+
+    // MARK: - BannerDataStore
+
+    private let bannerSubject = PassthroughSubject<Banner, Never>()
+    private let network: MockBannerNetworkStateController = .init()
+    private var cancellables = Set<AnyCancellable>()
+
+    /// Creates a new `BannerDataStore`
+    init() {
+
+        let networkPublisher = network.publisher.prepend(.notStarted)
+        let additionalActions = networkPublisher.compactMap { $0.banner }.map { Action.updateBannerLocally($0) }
+
+        bannerSubject
+            .prepend(state.banner)
+            .combineLatest(network.publisher.prepend(.notStarted))
+            .map { banner, networkState in
+                return State(banner: banner, networkState: networkState)
+            }
+            .assign(to: &$state)
+
+        pipeActions(publisher: additionalActions, storeIn: &cancellables)
+    }
+
+    // MARK: - Store
+
+    func send(_ action: Action) {
+        switch action {
+        case .updateBannerLocally(let banner):
+            bannerSubject.send(banner)
+        case .uploadBanner(let banner):
+            network.upload(banner: banner)
+        case .clearNetworkingState:
+            network.reset()
+        }
+    }
+
+}

Example/Photos/With Stores/Banner Feature/MockBannerNetworkStateController.swift

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+//
+//  MockBannerNetworkStateController.swift
+//  ViewStore
+//
+//  Created by Kenneth Ackerson on 4/3/23.
+//
+
+import Foundation
+import Combine
+
+/// A really contrived fake interface similar to networking state controller for updating `Banner` models on a nonexistent server.
+final class MockBannerNetworkStateController {
+
+    /// Represents the state of a network request for a banner.
+    enum NetworkState {
+
+        /// The network request has not started yet.
+        case notStarted
+
+        /// The network request is currently in progress.
+        case inProgress
+
+        /// The network request has finished and resulted in either success or failure.
+        /// - Parameter Result: A result type containing a `Banner` on success or a `NetworkError` on failure.
+        case finished(Result<Banner, NetworkError>)
+
+        /// The `Banner` object obtained from a successful network request, if available.
+        var banner: Banner? {
+            switch self {
+            case .inProgress, .notStarted:
+                return nil
+            case .finished(let result):
+                return try? result.get()
+            }
+        }
+
+        /// The error obtained from a failed network request, if available.
+        var error: NetworkError? {
+            switch self {
+            case .notStarted, .inProgress:
+                return nil
+            case .finished(let result):
+                do {
+                    _ = try result.get()
+                    return nil
+                } catch let error as NetworkError {
+                    return error
+                } catch {
+                    assertionFailure("unhandled error")
+                    return nil
+                }
+            }
+        }
+
+        /// Possible errors that can occur when using this controller.
+        enum NetworkError: LocalizedError {
+
+            /// A mocked error that is expected.
+            case intentionalFailure
+
+            // MARK - LocalizedError
+
+            var errorDescription: String? {
+                switch self {
+                case .intentionalFailure:
+                    return "This is an expected error used for testing error handling."
+                }
+            }
+        }
+    }
+
+    /// A publisher that sends updates of the `NetworkState`.
+    public var publisher: PassthroughSubject<NetworkState, Never> = .init()
+
+    /// Uploads a `Banner` to a fake server.
+    /// - Parameter banner: The `Banner` to upload.
+    func upload(banner: Banner) {
+        self.publisher.send(.inProgress)
+
+        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
+
+            // Pick whether you would like to get a successful (`.finished(.success...`) state or any error for this "network request".
+
+            //self.publisher.send(.finished(.success(banner)))
+
+            self.publisher.send(.finished(.failure(.intentionalFailure)))
+
+        }
+
+    }
+
+    /// Resets the current networking state to `notStarted`.
+    func reset() {
+        self.publisher.send(.notStarted)
+    }
+
+}

Example/Photos/With Stores/Banner Feature/View Level/BannerUpdateView.swift

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+//
+//  BannerUpdateView.swift
+//  ViewStore
+//
+//  Created by Kenneth Ackerson on 4/3/23.
+//
+
+import Foundation
+import SwiftUI
+import Combine
+
+/// A really simple view that allows you to type and upload a new Banner.
+struct BannerUpdateView<Store: BannerUpdateViewStoreType>: View {
+
+    @Environment(\.dismiss) private var dismiss
+
+    @StateObject private var store: Store
+
+    /// Creates a new `BannerUpdateView`.
+    /// - Parameter store: The `Store` that drives this view.
+    init(store: @autoclosure @escaping () -> Store) {
+        self._store = StateObject(wrappedValue: store())
+    }
+
+    var body: some View {
+        VStack {
+
+            VStack {
+                Spacer()
+
+                TextField("", text: store.workingTitle)
+                    .multilineTextAlignment(.center)
+                    .padding(10)
+                    .font(.system(size: 36))
+
+                Spacer()
+            }
+            .padding(.horizontal, 30)
+
+            Button {
+                store.send(.submit)
+            } label: {
+                Group {
+                    if store.state.dismissable {
+                        Text("Submit")
+                    } else {
+                        ProgressView()
+                    }
+                }
+                .foregroundColor(.white)
+                .padding(.vertical, 20)
+                .padding(.horizontal, 40)
+                .background {
+                    RoundedRectangle(cornerRadius: 10)
+                        .foregroundColor(.blue)
+                }
+            }
+            .disabled(!store.state.dismissable)
+            .padding(.bottom, 10)
+        }
+        .onChange(of: store.state.success) { success in
+            if success {
+                dismiss()
+            }
+        }
+        .alert(isPresented: store.isErrorPresented, error: store.state.error) { _ in
+
+        } message: { error in
+            Text("Error")
+        }
+
+    }
+}

Example/Photos/With Stores/Banner Feature/View Level/BannerUpdateViewStore.swift

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+//
+//  BannerUpdateViewStore.swift
+//  ViewStore
+//
+//  Created by Kenneth Ackerson on 4/3/23.
+//
+
+import Foundation
+import Combine
+import SwiftUI
+import CasePaths
+
+typealias BannerUpdateViewStoreType = Store<BannerUpdateViewStore.State, BannerUpdateViewStore.Action>
+
+/// A `Store` that drives a view that can update a `Banner` through any `BannerDataStoreType`, and exposes view-specific state such as a working copy of the banner, the possible networking error, etc.
+final class BannerUpdateViewStore: Store {
+
+    // MARK: - Store
+
+    /// Represents the state of the `BannerUpdateViewStore`
+    struct State {
+        /// Stores the state of the nested `BannerDataStore`
+        let bannerViewState: BannerDataStore.State
+
+        /// A working copy of the banner being updated, to be uploaded if the `submit` action is sent.
+        let workingCopy: Banner
+
+        /// Returns true if the network state is not started or finished, false if it's in progress
+        var dismissable: Bool {
+            switch bannerViewState.networkState {
+            case .notStarted, .finished:
+                return true
+            case .inProgress:
+                return false
+            }
+        }
+
+        /// Returns true if the network state is finished and the result is successful, false otherwise
+        var success: Bool {
+            switch bannerViewState.networkState {
+            case .notStarted, .inProgress:
+                return false
+            case .finished(let result):
+                return (try? result.get()) != nil
+            }
+        }
+
+        // Returns a `NetworkError` if there is an error in the network state when it's finished, otherwise returns nil
+        var error: MockBannerNetworkStateController.NetworkState.NetworkError? {
+            return bannerViewState.networkState.error
+        }
+    }
+
+    enum Action {
+        /// Action to update the title of the banner with a given string
+        case updateTitle(String)
+
+        /// Action to dismiss an error
+        case dismissError
+
+        /// Action to submit the updated working copy banner to the network
+        case submit
+    }
+
+    @Published var state: State
+    var publishedState: AnyPublisher<State, Never> {
+        return $state.eraseToAnyPublisher()
+    }
+
+    // MARK: - BannerUpdateViewStore
+
+    private let bannerDataStore: any BannerDataStoreType
+
+    private let newTitlePublisher = PassthroughSubject<String, Never>()
+
+    /// Creates a new `BannerUpdateViewStore`.
+    /// - Parameter bannerDataStore: The data `Store` responsible for updating the banner on the network and its source of truth in the application.
+    init(bannerDataStore: any BannerDataStoreType) {
+        self.bannerDataStore = bannerDataStore
+
+        state = State(bannerViewState: bannerDataStore.state, workingCopy: bannerDataStore.state.banner)
+
+        bannerDataStore
+            .publishedState
+            .combineLatest(newTitlePublisher.map(Banner.init).prepend(state.workingCopy))
+            .map { bannerState, workingCopy in
+                State(bannerViewState: bannerState, workingCopy: workingCopy)
+            }
+            .assign(to: &$state)
+    }
+
+    // MARK: - Store
+
+    func send(_ action: Action) {
+        switch action {
+        case .updateTitle(let title):
+            newTitlePublisher.send(title)
+        case .submit:
+            bannerDataStore.send(.uploadBanner(state.workingCopy))
+        case .dismissError:
+            bannerDataStore.send(.clearNetworkingState)
+        }
+    }
+
+}
+
+extension BannerUpdateViewStoreType {
+    /// Computed property that creates a binding for the working title
+    var workingTitle: Binding<String> {
+        makeBinding(stateKeyPath: \.workingCopy.title, actionCasePath: /Action.updateTitle)
+    }
+
+    /// Computed property that creates a binding for the error presentation state
+    var isErrorPresented: Binding<Bool> {
+        .init(get: {
+            return self.state.error != nil
+        }, set: { _ in
+            self.send(.dismissError)
+        })
+    }
+}