State Container

Yolo.xcodeproj/project.pbxproj

@@ -3,10 +3,18 @@
 	archiveVersion = 1;
 	classes = {
 	};
-	objectVersion = 50;
+	objectVersion = 52;
 	objects = {
 
 /* Begin PBXBuildFile section */
+		6A08AA7026AF29CA00BA287C /* StateContainerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA6F26AF29CA00BA287C /* StateContainerTests.swift */; };
+		6A08AA7226AF3B9600BA287C /* StateContainer.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7126AF3B9600BA287C /* StateContainer.swift */; };
+		6A08AA7426AF3F9700BA287C /* RootMapperTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7326AF3F9700BA287C /* RootMapperTests.swift */; };
+		6A08AA7726AFD04100BA287C /* OrderedCollections in Frameworks */ = {isa = PBXBuildFile; productRef = 6A08AA7626AFD04100BA287C /* OrderedCollections */; };
+		6A08AA7926AFD28D00BA287C /* FeedMapperTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7826AFD28D00BA287C /* FeedMapperTests.swift */; };
+		6A08AA7B26AFDD4B00BA287C /* Memoize.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7A26AFDD4B00BA287C /* Memoize.swift */; };
+		6A08AA7D26AFDE7800BA287C /* Selector.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7C26AFDE7800BA287C /* Selector.swift */; };
+		6A08AA7F26AFE0D400BA287C /* FeedSelectorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A08AA7E26AFE0D400BA287C /* FeedSelectorTests.swift */; };
 		6A137528263BEB4D003F0E5D /* Content.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A137527263BEB4D003F0E5D /* Content.swift */; };
 		6A13752F263BEC40003F0E5D /* ContentResponseMapper.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A13752E263BEC40003F0E5D /* ContentResponseMapper.swift */; };
 		6A137537263BED60003F0E5D /* ContentResponseMapperTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A137536263BED60003F0E5D /* ContentResponseMapperTests.swift */; };
@@ -101,6 +109,13 @@
 /* End PBXContainerItemProxy section */
 
 /* Begin PBXFileReference section */
+		6A08AA6F26AF29CA00BA287C /* StateContainerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StateContainerTests.swift; sourceTree = "<group>"; };
+		6A08AA7126AF3B9600BA287C /* StateContainer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StateContainer.swift; sourceTree = "<group>"; };
+		6A08AA7326AF3F9700BA287C /* RootMapperTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RootMapperTests.swift; sourceTree = "<group>"; };
+		6A08AA7826AFD28D00BA287C /* FeedMapperTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedMapperTests.swift; sourceTree = "<group>"; };
+		6A08AA7A26AFDD4B00BA287C /* Memoize.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Memoize.swift; sourceTree = "<group>"; };
+		6A08AA7C26AFDE7800BA287C /* Selector.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Selector.swift; sourceTree = "<group>"; };
+		6A08AA7E26AFE0D400BA287C /* FeedSelectorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FeedSelectorTests.swift; sourceTree = "<group>"; };
 		6A137527263BEB4D003F0E5D /* Content.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Content.swift; sourceTree = "<group>"; };
 		6A13752E263BEC40003F0E5D /* ContentResponseMapper.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ContentResponseMapper.swift; sourceTree = "<group>"; };
 		6A137536263BED60003F0E5D /* ContentResponseMapperTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ContentResponseMapperTests.swift; sourceTree = "<group>"; };
@@ -200,12 +215,24 @@
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				6A08AA7726AFD04100BA287C /* OrderedCollections in Frameworks */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
 /* End PBXFrameworksBuildPhase section */
 
 /* Begin PBXGroup section */
+		6A08AA6E26AF29B800BA287C /* Helpers */ = {
+			isa = PBXGroup;
+			children = (
+				6A08AA6F26AF29CA00BA287C /* StateContainerTests.swift */,
+				6A08AA7326AF3F9700BA287C /* RootMapperTests.swift */,
+				6A08AA7826AFD28D00BA287C /* FeedMapperTests.swift */,
+				6A08AA7E26AFE0D400BA287C /* FeedSelectorTests.swift */,
+			);
+			path = Helpers;
+			sourceTree = "<group>";
+		};
 		6A137525263BEAFD003F0E5D /* Content */ = {
 			isa = PBXGroup;
 			children = (
@@ -447,6 +474,7 @@
 			isa = PBXGroup;
 			children = (
 				6A30B9C42639EA1700A65598 /* Info.plist */,
+				6A08AA6E26AF29B800BA287C /* Helpers */,
 				6A30B9CE2639EA4C00A65598 /* Modules */,
 				6A45D7A7263A62B8003EF1C8 /* Scenes */,
 				6A30B9DC2639EB4300A65598 /* TestHelpers */,
@@ -616,6 +644,9 @@
 				6AE78CA7263C42F500E350FB /* Interactions+Toggle.swift */,
 				6A45D7CE263A78CB003EF1C8 /* Publisher+MainQueue.swift */,
 				6AE02CAE263B1E310089B39F /* ResourcePresentationAdapter.swift */,
+				6A08AA7126AF3B9600BA287C /* StateContainer.swift */,
+				6A08AA7A26AFDD4B00BA287C /* Memoize.swift */,
+				6A08AA7C26AFDE7800BA287C /* Selector.swift */,
 			);
 			path = Helpers;
 			sourceTree = "<group>";
@@ -843,6 +874,9 @@
 			dependencies = (
 			);
 			name = Yolo;
+			packageProductDependencies = (
+				6A08AA7626AFD04100BA287C /* OrderedCollections */,
+			);
 			productName = Yolo;
 			productReference = 6A79BE792639D918000062A7 /* Yolo.app */;
 			productType = "com.apple.product-type.application";
@@ -875,6 +909,9 @@
 				Base,
 			);
 			mainGroup = 6A79BE702639D918000062A7;
+			packageReferences = (
+				6A08AA7526AFD04100BA287C /* XCRemoteSwiftPackageReference "swift-collections" */,
+			);
 			productRefGroup = 6A79BE7A2639D918000062A7 /* Products */;
 			projectDirPath = "";
 			projectRoot = "";
@@ -915,13 +952,17 @@
 			files = (
 				6A8F261F263C5B07008E86F6 /* FeedUIIntegrationTests+LoaderSpy.swift in Sources */,
 				6A8F2619263C5AD3008E86F6 /* FeedUIIntegrationTests+Assertions.swift in Sources */,
+				6A08AA7F26AFE0D400BA287C /* FeedSelectorTests.swift in Sources */,
 				6A45D827263AE77A003EF1C8 /* FeedCardView+TestHelpers.swift in Sources */,
 				6A8F2606263C5999008E86F6 /* ContentUIIntergrationTests+Assertions.swift in Sources */,
 				6A8F2623263C5B5B008E86F6 /* UIView+LayoutCycle.swift in Sources */,
+				6A08AA7926AFD28D00BA287C /* FeedMapperTests.swift in Sources */,
 				6A30B9E42639EB6B00A65598 /* XCTestCase+Error.swift in Sources */,
 				6A30B9D32639EA6700A65598 /* URLProtocolStub.swift in Sources */,
 				6A30B9DE2639EB5800A65598 /* XCTestCase+Data.swift in Sources */,
+				6A08AA7026AF29CA00BA287C /* StateContainerTests.swift in Sources */,
 				6A8F260E263C59F8008E86F6 /* ContentView+TestHelpers.swift in Sources */,
+				6A08AA7426AF3F9700BA287C /* RootMapperTests.swift in Sources */,
 				6A45D837263AE998003EF1C8 /* ImageResponseMapperTests.swift in Sources */,
 				6A45D7F0263A85B3003EF1C8 /* FeedSnapshotTests.swift in Sources */,
 				6AC229EC263C2B3D0061718F /* InteractionResposneMapperTests.swift in Sources */,
@@ -959,6 +1000,7 @@
 				6A13752F263BEC40003F0E5D /* ContentResponseMapper.swift in Sources */,
 				6A137556263BFEF7003F0E5D /* ContentViewController.swift in Sources */,
 				6AE02CAB263B19DC0089B39F /* ResourcePresenter.swift in Sources */,
+				6A08AA7B26AFDD4B00BA287C /* Memoize.swift in Sources */,
 				6A137528263BEB4D003F0E5D /* Content.swift in Sources */,
 				6A45D814263AE262003EF1C8 /* Combine+Helpers.swift in Sources */,
 				6AE02CCB263B326E0089B39F /* UITableView+Dequeueing.swift in Sources */,
@@ -983,6 +1025,7 @@
 				6AC229E5263C2AE50061718F /* Interactions.swift in Sources */,
 				6A26214D263BDC7C00956E14 /* CommentPresenter.swift in Sources */,
 				6AE02CD9263B41810089B39F /* ResourceViewAdapter.swift in Sources */,
+				6A08AA7D26AFDE7800BA287C /* Selector.swift in Sources */,
 				6AE78CA8263C42F500E350FB /* Interactions+Toggle.swift in Sources */,
 				6AC229DE263C2A4E0061718F /* InteractionResposneMapper.swift in Sources */,
 				6A45D82F263AE911003EF1C8 /* ImageResponseMapper.swift in Sources */,
@@ -995,6 +1038,7 @@
 				6A45D7C0263A6E65003EF1C8 /* FeedUIComposer.swift in Sources */,
 				6A45D7E5263A7C8A003EF1C8 /* FeedCardCellController.swift in Sources */,
 				6A26215A263BDE7A00956E14 /* CommentCellController.swift in Sources */,
+				6A08AA7226AF3B9600BA287C /* StateContainer.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -1252,6 +1296,25 @@
 			defaultConfigurationName = Release;
 		};
 /* End XCConfigurationList section */
+
+/* Begin XCRemoteSwiftPackageReference section */
+		6A08AA7526AFD04100BA287C /* XCRemoteSwiftPackageReference "swift-collections" */ = {
+			isa = XCRemoteSwiftPackageReference;
+			repositoryURL = "https://github.com/apple/swift-collections";
+			requirement = {
+				kind = upToNextMajorVersion;
+				minimumVersion = 0.0.4;
+			};
+		};
+/* End XCRemoteSwiftPackageReference section */
+
+/* Begin XCSwiftPackageProductDependency section */
+		6A08AA7626AFD04100BA287C /* OrderedCollections */ = {
+			isa = XCSwiftPackageProductDependency;
+			package = 6A08AA7526AFD04100BA287C /* XCRemoteSwiftPackageReference "swift-collections" */;
+			productName = OrderedCollections;
+		};
+/* End XCSwiftPackageProductDependency section */
 	};
 	rootObject = 6A79BE712639D918000062A7 /* Project object */;
 }

Yolo/Application/SceneDelegate.swift

@@ -23,9 +23,14 @@ class SceneDelegate: UIResponder, UIWindowSceneDelegate {
 
     private lazy var baseURL = URL(string: "https://powerful-wave-91495.herokuapp.com/")!
 
-    convenience init(httpClient: HTTPClient) {
+    private lazy var store: Store = {
+        Store(state: nil, mapper: rootMapper)
+    }()
+
+    convenience init(httpClient: HTTPClient, store: Store) {
         self.init()
         self.httpClient = httpClient
+        self.store = store
     }
 
     func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
@@ -81,8 +86,11 @@ private extension SceneDelegate {
         return httpClient
             .dispatchPublisher(for: request)
             .tryMap(FeedResponseMapper.map)
-            .map { $0.items }
-            .eraseToAnyPublisher()
+            .map(\.items)
+            .handleEvents(receiveOutput: { [store] items in
+                store.dispatch(FeedLoadedEvent(payload: items))
+            })
+            .select(from: store, using: feedSelector)
     }
 
     func makeRemoteImageLoader(_ imageURL: URL) -> AnyPublisher<Data, Error> {
@@ -128,6 +136,7 @@ private extension SceneDelegate {
     }
 
     func makeRemoteInteractionService(id: String, interaction: Interaction) -> AnyPublisher<Interactions, Error> {
+        store.dispatch(LikeInteractionEvent(payload: (id, interaction == .like)))
         var request = URLRequest(
             url: baseURL
                 .appendingPathComponent("interactions")

Yolo/Helpers/Combine+Helpers.swift

@@ -23,3 +23,9 @@ extension HTTPClient {
         .eraseToAnyPublisher()
     }
 }
+
+extension Publisher {
+    func select(from store: Store, using selector: @escaping (AppState) -> Output) -> AnyPublisher<Output, Failure> {
+        flatMap { _ in store.state.map(selector).setFailureType(to: Failure.self) }.eraseToAnyPublisher()
+    }
+}

Yolo/Helpers/Memoize.swift

@@ -0,0 +1,21 @@
+//
+//  Memoize.swift
+//  Yolo
+//
+//  Created by Gordon Smith on 27/07/2021.
+//
+
+import Foundation
+
+func memoize<T: Hashable, U>(_ fn: @escaping (T) -> U) -> (T) -> U {
+    var memo = Dictionary<T, U>()
+
+    func result(selector: T) -> U {
+        if let q = memo[selector] { return q }
+        let r = fn(selector)
+        memo[selector] = r
+        return r
+    }
+
+    return result
+}

Yolo/Helpers/Selector.swift

@@ -0,0 +1,14 @@
+//
+//  Selector.swift
+//  Yolo
+//
+//  Created by Gordon Smith on 27/07/2021.
+//
+
+import Foundation
+
+func createSelector<TInput: Hashable, TOutput, T1>(selector1: @escaping (TInput) -> T1, _ combine: @escaping (T1) -> TOutput) -> (TInput) -> TOutput {
+    memoize { value in
+        combine(selector1(value))
+    }
+}

Yolo/Helpers/StateContainer.swift

@@ -0,0 +1,101 @@
+//
+//  StateContainer.swift
+//  Yolo
+//
+//  Created by Gordon Smith on 26/07/2021.
+//
+
+import Foundation
+import Combine
+import OrderedCollections
+
+public protocol Event { }
+
+public typealias StateMapper<T> = (_ state: T?, _ event: Event) -> T
+
+typealias Store = StateContainer<AppState>
+
+public final class StateContainer<T> {
+    private(set) public var state: CurrentValueSubject<T, Never>
+    private let mapper: StateMapper<T>
+
+    public init(state: T?, mapper: @escaping StateMapper<T>) {
+        if let state = state {
+            self.state = .init(state)
+        } else {
+            self.state = .init(mapper(nil, StateInit()))
+        }
+        self.mapper = mapper
+    }
+
+    public func dispatch(_ event: Event) {
+        let next = mapper(state.value, event)
+        state.send(next)
+    }
+}
+
+private extension StateContainer {
+    struct StateInit: Event { }
+}
+
+public struct AppState: Hashable {
+    let feed: FeedState
+    public init(feed: FeedState = .init()) {
+        self.feed = feed
+    }
+}
+
+public let rootMapper: StateMapper<AppState> = { state, event in
+    AppState(
+        feed: feedMapper(state?.feed, event)
+    )
+}
+
+public struct FeedLoadedEvent: Event {
+    public let payload: [FeedItem]
+    public init(payload: [FeedItem]) {
+        self.payload = payload
+    }
+}
+
+public struct FeedState: Hashable {
+    public var items: OrderedDictionary<String, FeedItem>
+    public init(items: OrderedDictionary<String, FeedItem> = [:]) {
+        self.items = items
+    }
+}
+
+public let feedMapper: StateMapper<FeedState> = { state, event in
+    var state = state ?? FeedState()
+
+    if let event = event as? FeedLoadedEvent {
+        event.payload.forEach { item in
+            state.items[item.id] = item
+        }
+        return state
+    }
+
+    if let event = event as? LikeInteractionEvent, let item = state.items[event.payload.id] {
+        state.items[event.payload.id] = event.payload.isLiked ? item.cloneAsLiked() : item.cloneAsUnliked()
+        return state
+    }
+
+    return state
+}
+
+public let stateSelector = { (state: AppState) in state }
+public let feedSelector = createSelector(selector1: stateSelector, { state -> [FeedItem] in
+    let feed = state.feed
+    return feed.items.reduce([FeedItem]()) { acc, e in
+        var acc = acc
+        acc.append(e.value)
+        return acc
+    }
+})
+
+public struct LikeInteractionEvent: Event {
+    public let payload: (id: String, isLiked: Bool)
+    public init(payload: (id: String, isLiked: Bool)) {
+        self.payload = payload
+    }
+}