Add WorkflowSwiftUIExperimental

Development.podspec

@@ -17,6 +17,7 @@ Pod::Spec.new do |s|
   s.dependency 'WorkflowRxSwift'
   s.dependency 'WorkflowCombine'
   s.dependency 'WorkflowConcurrency'
+  s.dependency 'WorkflowSwiftUIExperimental'
   s.dependency 'ViewEnvironment'
   s.dependency 'ViewEnvironmentUI'
 

WorkflowSwiftUIExperimental.podspec

@@ -0,0 +1,25 @@
+require_relative('version')
+
+Pod::Spec.new do |s|
+    s.name         = 'WorkflowSwiftUIExperimental'
+    s.version      = '0.1'
+    s.summary      = 'Infrastructure for Workflow-powered SwiftUI'
+    s.homepage     = 'https://www.github.com/square/workflow-swift'
+    s.license      = 'Apache License, Version 2.0'
+    s.author       = 'Square'
+    s.source       = { :git => 'https://github.com/square/workflow-swift.git', :tag => "swiftui-experimental/v#{s.version}" }
+
+    # 1.7 is needed for `swift_versions` support
+    s.cocoapods_version = '>= 1.7.0'
+
+    s.swift_versions = [WORKFLOW_SWIFT_VERSION]
+    s.ios.deployment_target = WORKFLOW_IOS_DEPLOYMENT_TARGET
+    s.osx.deployment_target = WORKFLOW_MACOS_DEPLOYMENT_TARGET
+
+    s.source_files = 'WorkflowSwiftUIExperimental/Sources/*.swift'
+
+    s.dependency 'Workflow', WORKFLOW_VERSION
+    s.dependency 'WorkflowUI', WORKFLOW_VERSION
+
+    s.pod_target_xcconfig = { 'APPLICATION_EXTENSION_API_ONLY' => 'YES' }
+  end

WorkflowSwiftUIExperimental/README.md

@@ -0,0 +1,11 @@
+# WorkflowSwiftUIExperimental
+
+Experimental extensions to Workflow for writing Screens in SwiftUI.
+
+## Versioning
+
+Because this module is experimental, it is versioned separately from other modules in Workflow. You should bump its version as part of any pull request that changes it, and need not bump its version in PRs that change only other modules.
+
+Per semantic versioning, its major version remains at `0`, and only its minor version is incremented. Any increase in the minor version may come with breaking changes.
+
+To bump the minor version, update `s.version` in `WorkflowSwiftUIExperimental.podspec`.

WorkflowSwiftUIExperimental/Sources/EnvironmentValues+ViewEnvironment.swift

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2023 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import SwiftUI
+import WorkflowUI
+
+private struct ViewEnvironmentKey: EnvironmentKey {
+    static let defaultValue: ViewEnvironment = .empty
+}
+
+public extension EnvironmentValues {
+    var viewEnvironment: ViewEnvironment {
+        get { self[ViewEnvironmentKey.self] }
+        set { self[ViewEnvironmentKey.self] = newValue }
+    }
+}

WorkflowSwiftUIExperimental/Sources/ObservableValue+Binding.swift

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2023 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if canImport(UIKit)
+
+import SwiftUI
+
+public extension ObservableValue {
+    func binding<T>(
+        get: @escaping (Value) -> T,
+        set: @escaping (Value) -> (T) -> Void
+    ) -> Binding<T> {
+        // This convoluted way of creating a `Binding`, relative to `Binding.init(get:set:)`, is
+        // a workaround borrowed from TCA for a SwiftUI issue:
+        // https://github.com/pointfreeco/swift-composable-architecture/pull/770
+        ObservedObject(wrappedValue: self)
+            .projectedValue[get: .init(rawValue: get), set: .init(rawValue: set)]
+    }
+
+    private subscript<T>(
+        get get: HashableWrapper<(Value) -> T>,
+        set set: HashableWrapper<(Value) -> (T) -> Void>
+    ) -> T {
+        get { get.rawValue(value) }
+        set { set.rawValue(value)(newValue) }
+    }
+
+    private struct HashableWrapper<Value>: Hashable {
+        let rawValue: Value
+        static func == (lhs: Self, rhs: Self) -> Bool { false }
+        func hash(into hasher: inout Hasher) {}
+    }
+}
+
+#endif

WorkflowSwiftUIExperimental/Sources/ObservableValue.swift

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2023 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import Combine
+import Workflow
+
+@dynamicMemberLookup
+public final class ObservableValue<Value>: ObservableObject {
+    private var internalValue: Value
+    private let subject = PassthroughSubject<Value, Never>()
+    private var cancellable: AnyCancellable?
+    private let isEquivalent: ((Value, Value) -> Bool)?
+
+    public private(set) var value: Value {
+        get {
+            return internalValue
+        }
+        set {
+            subject.send(newValue)
+        }
+    }
+
+    public private(set) lazy var objectWillChange = ObservableObjectPublisher()
+    private var parentCancellable: AnyCancellable?
+
+    public static func makeObservableValue(
+        _ value: Value,
+        isEquivalent: ((Value, Value) -> Bool)? = nil
+    ) -> (ObservableValue, Sink<Value>) {
+        let observableValue = ObservableValue(value: value, isEquivalent: isEquivalent)
+        let sink = Sink { newValue in
+            observableValue.value = newValue
+        }
+
+        return (observableValue, sink)
+    }
+
+    private init(value: Value, isEquivalent: ((Value, Value) -> Bool)?) {
+        self.internalValue = value
+        self.isEquivalent = isEquivalent
+        self.cancellable = valuePublisher()
+            .dropFirst()
+            .sink { [weak self] newValue in
+                guard let self = self else { return }
+                self.objectWillChange.send()
+                self.internalValue = newValue
+            }
+        // Allows removeDuplicates operator to have the initial value.
+        subject.send(value)
+    }
+
+    //// Scopes the ObservableValue to a subset of Value to LocalValue given the supplied closure while allowing to optionally remove duplicates.
+    /// - Parameters:
+    ///   - toLocalValue: A closure that takes a Value and returns a LocalValue.
+    ///   - isEquivalent: An optional closure that checks to see if a LocalValue is equivalent.
+    /// - Returns: a scoped ObservableValue of LocalValue.
+    public func scope<LocalValue>(_ toLocalValue: @escaping (Value) -> LocalValue, isEquivalent: ((LocalValue, LocalValue) -> Bool)? = nil) -> ObservableValue<LocalValue> {
+        return scopeToLocalValue(toLocalValue, isEquivalent: isEquivalent)
+    }
+
+    /// Scopes the ObservableValue to a subset of Value to LocalValue given the supplied closure and removes duplicate values using Equatable.
+    /// - Parameter toLocalValue: A closure that takes a Value and returns a LocalValue.
+    /// - Returns: a scoped ObservableValue of LocalValue.
+    public func scope<LocalValue>(_ toLocalValue: @escaping (Value) -> LocalValue) -> ObservableValue<LocalValue> where LocalValue: Equatable {
+        return scopeToLocalValue(toLocalValue, isEquivalent: { $0 == $1 })
+    }
+
+    /// Returns the value at the given keypath of ``Value``.
+    ///
+    /// In combination with `@dynamicMemberLookup`, this allows us to write `model.myProperty` instead of
+    /// `model.value.myProperty` where `model` has type `ObservableValue<T>`.
+    public subscript<T>(dynamicMember keyPath: KeyPath<Value, T>) -> T {
+        internalValue[keyPath: keyPath]
+    }
+
+    private func scopeToLocalValue<LocalValue>(_ toLocalValue: @escaping (Value) -> LocalValue, isEquivalent: ((LocalValue, LocalValue) -> Bool)? = nil) -> ObservableValue<LocalValue> {
+        let localObservableValue = ObservableValue<LocalValue>(
+            value: toLocalValue(internalValue),
+            isEquivalent: isEquivalent
+        )
+        localObservableValue.parentCancellable = valuePublisher().sink(receiveValue: { newValue in
+            localObservableValue.value = toLocalValue(newValue)
+        })
+        return localObservableValue
+    }
+
+    private func valuePublisher() -> AnyPublisher<Value, Never> {
+        guard let isEquivalent = isEquivalent else {
+            return subject.eraseToAnyPublisher()
+        }
+
+        return subject.removeDuplicates(by: isEquivalent).eraseToAnyPublisher()
+    }
+}

WorkflowSwiftUIExperimental/Sources/SwiftUIScreen.swift

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2023 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if canImport(UIKit)
+
+import SwiftUI
+import Workflow
+import WorkflowUI
+
+public protocol SwiftUIScreen: Screen {
+    associatedtype Content: View
+
+    @ViewBuilder
+    static func makeView(model: ObservableValue<Self>) -> Content
+
+    static var isEquivalent: ((Self, Self) -> Bool)? { get }
+}
+
+public extension SwiftUIScreen {
+    static var isEquivalent: ((Self, Self) -> Bool)? { return nil }
+}
+
+public extension SwiftUIScreen where Self: Equatable {
+    static var isEquivalent: ((Self, Self) -> Bool)? { { $0 == $1 } }
+}
+
+public extension SwiftUIScreen {
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        ViewControllerDescription(
+            type: ModeledHostingController<Self, WithModel<Self, EnvironmentInjectingView<Content>>>.self,
+            environment: environment,
+            build: {
+                let (model, modelSink) = ObservableValue.makeObservableValue(self, isEquivalent: Self.isEquivalent)
+                let (viewEnvironment, envSink) = ObservableValue.makeObservableValue(environment)
+                return ModeledHostingController(
+                    modelSink: modelSink,
+                    viewEnvironmentSink: envSink,
+                    rootView: WithModel(model, content: { model in
+                        EnvironmentInjectingView(
+                            viewEnvironment: viewEnvironment,
+                            content: Self.makeView(model: model)
+                        )
+                    })
+                )
+            },
+            update: {
+                $0.modelSink.send(self)
+                $0.viewEnvironmentSink.send(environment)
+            }
+        )
+    }
+}
+
+private struct EnvironmentInjectingView<Content: View>: View {
+    @ObservedObject var viewEnvironment: ObservableValue<ViewEnvironment>
+    let content: Content
+
+    var body: some View {
+        content
+            .environment(\.viewEnvironment, viewEnvironment.value)
+    }
+}
+
+private final class ModeledHostingController<Model, Content: View>: UIHostingController<Content> {
+    let modelSink: Sink<Model>
+    let viewEnvironmentSink: Sink<ViewEnvironment>
+
+    init(modelSink: Sink<Model>, viewEnvironmentSink: Sink<ViewEnvironment>, rootView: Content) {
+        self.modelSink = modelSink
+        self.viewEnvironmentSink = viewEnvironmentSink
+
+        super.init(rootView: rootView)
+    }
+
+    required init?(coder aDecoder: NSCoder) {
+        fatalError("not implemented")
+    }
+}
+
+#endif

WorkflowSwiftUIExperimental/Sources/WithModel.swift

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2023 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import SwiftUI
+
+struct WithModel<Model, Content: View>: View {
+    @ObservedObject private var model: ObservableValue<Model>
+    private let content: (ObservableValue<Model>) -> Content
+
+    init(
+        _ model: ObservableValue<Model>,
+        @ViewBuilder content: @escaping (ObservableValue<Model>) -> Content
+    ) {
+        self.model = model
+        self.content = content
+    }
+
+    var body: Content {
+        content(model)
+    }
+}