Add a recipe for presenter integration with SwiftUI "renderers" (amzn#157)

* Add a recipe to show how presenters can be launched from iOS native and how we can render the models using SwiftUI rather than renderers.

See amzn#154

Author: JessalynWang

recipes/app/src/commonMain/kotlin/software/amazon/app/platform/recipes/AppComponent.kt

@@ -2,6 +2,8 @@ package software.amazon.app.platform.recipes
 
 import me.tatarka.inject.annotations.IntoSet
 import me.tatarka.inject.annotations.Provides
+import software.amazon.app.platform.presenter.molecule.MoleculeScopeFactory
+import software.amazon.app.platform.recipes.swiftui.SwiftUiHomePresenter
 import software.amazon.app.platform.scope.Scoped
 import software.amazon.app.platform.scope.coroutine.CoroutineScopeScoped
 import software.amazon.lastmile.kotlin.inject.anvil.AppScope
@@ -28,4 +30,10 @@ interface AppComponent {
    * needed.
    */
   @Provides @IntoSet @ForScope(AppScope::class) fun provideEmptyScoped(): Scoped = Scoped.NO_OP
+
+  /** The root presenter for the SwiftUI recipe. */
+  val swiftUiHomePresenter: SwiftUiHomePresenter
+
+  /** Factory needed to launch presenters from native. */
+  val moleculeScopeFactory: MoleculeScopeFactory
 }

recipes/app/src/commonMain/kotlin/software/amazon/app/platform/recipes/DemoApplication.kt

@@ -4,6 +4,7 @@ import software.amazon.app.platform.scope.RootScopeProvider
 import software.amazon.app.platform.scope.Scope
 import software.amazon.app.platform.scope.coroutine.addCoroutineScopeScoped
 import software.amazon.app.platform.scope.di.addKotlinInjectComponent
+import software.amazon.app.platform.scope.di.kotlinInjectComponent
 import software.amazon.app.platform.scope.register
 
 /**
@@ -17,6 +18,10 @@ class DemoApplication : RootScopeProvider {
   override val rootScope: Scope
     get() = checkNotNull(_rootScope) { "Must call create() first." }
 
+  /** Provides the application scope DI component. */
+  val appComponent: AppComponent
+    get() = rootScope.kotlinInjectComponent<AppComponent>()
+
   /** Creates the root scope and remembers the instance. */
   fun create(appComponent: AppComponent) {
     check(_rootScope == null) { "create() should be called only once." }

recipes/common/impl/src/commonMain/kotlin/software/amazon/app/platform/recipes/swiftui/SwiftUiChildPresenter.kt

@@ -0,0 +1,43 @@
+@file:Suppress("UndocumentedPublicProperty", "UndocumentedPublicClass")
+
+package software.amazon.app.platform.recipes.swiftui
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.produceState
+import androidx.compose.runtime.snapshots.SnapshotStateList
+import kotlin.time.Duration.Companion.seconds
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.isActive
+import software.amazon.app.platform.presenter.BaseModel
+import software.amazon.app.platform.presenter.molecule.MoleculePresenter
+import software.amazon.app.platform.recipes.swiftui.SwiftUiChildPresenter.Model
+
+class SwiftUiChildPresenter(
+  private val index: Int,
+  private val backstack: SnapshotStateList<MoleculePresenter<Unit, out BaseModel>>,
+) : MoleculePresenter<Unit, Model> {
+  @Composable
+  override fun present(input: Unit): Model {
+    val counter by
+      produceState(0) {
+        while (isActive) {
+          delay(1.seconds)
+          value += 1
+        }
+      }
+
+    return Model(index = index, counter = counter) {
+      when (it) {
+        Event.AddPeer ->
+          backstack.add(SwiftUiChildPresenter(index = index + 1, backstack = backstack))
+      }
+    }
+  }
+
+  data class Model(val index: Int, val counter: Int, val onEvent: (Event) -> Unit) : BaseModel
+
+  sealed interface Event {
+    data object AddPeer : Event
+  }
+}

recipes/common/impl/src/commonMain/kotlin/software/amazon/app/platform/recipes/swiftui/SwiftUiHomePresenter.kt

@@ -0,0 +1,65 @@
+@file:Suppress("UndocumentedPublicProperty", "UndocumentedPublicClass")
+
+package software.amazon.app.platform.recipes.swiftui
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.mutableStateListOf
+import androidx.compose.runtime.remember
+import me.tatarka.inject.annotations.Inject
+import software.amazon.app.platform.presenter.BaseModel
+import software.amazon.app.platform.presenter.molecule.MoleculePresenter
+import software.amazon.app.platform.recipes.swiftui.SwiftUiHomePresenter.Model
+
+/**
+ * A presenter that manages a backstack of presenters that are rendered by SwiftUI's
+ * `NavigationStack`. All presenters in this backstack are always active, because `NavigationStack`
+ * renders them on stack modification. In SwiftUI this is necessary as views remain alive even when
+ * they are no longer visible.
+ *
+ * A detail of note for this class is that we pass a list of [BaseModel] to the view but receive a
+ * list of [Int] back where each integer represents the position of a presenter in the backstack
+ * list. This is because to share control of state with `NavigationStack` we need to initialize the
+ * `NavigationStack` with a `Binding` to a collection of `Hashable` data values. [BaseModel] by
+ * default is not `Hashable` and we cannot extend it to conform to `Hashable` due to current
+ * Kotlin-Swift interop limitations. As such in Swift the list of [BaseModel] is converted to a list
+ * of indices, which are hashable by default. This should be sufficient to handle most navigation
+ * cases but if it is required to receive more information to determine how to modify the presenter
+ * backstack, it is possible to create a generic class that implements [BaseModel] and wrap that
+ * class in a hashable `struct`.
+ */
+@Inject
+class SwiftUiHomePresenter : MoleculePresenter<Unit, Model> {
+  @Composable
+  override fun present(input: Unit): Model {
+    val backstack = remember {
+      mutableStateListOf<MoleculePresenter<Unit, out BaseModel>>().apply {
+        // There must be always one element.
+        add(SwiftUiChildPresenter(index = 0, backstack = this))
+      }
+    }
+
+    return Model(modelBackstack = backstack.map { it.present(Unit) }) {
+      when (it) {
+        is Event.BackstackModificationEvent -> {
+          val updatedBackstack = it.indicesBackstack.map { index -> backstack[index] }
+
+          backstack.clear()
+          backstack.addAll(updatedBackstack)
+        }
+      }
+    }
+  }
+
+  /**
+   * Model that contains all the information needed for SwiftUI to render the backstack.
+   * [modelBackstack] contains the backage and [onEvent] exposes an event handling function that can
+   * be called by the binding that `NavigationStack` is initialized with.
+   */
+  data class Model(val modelBackstack: List<BaseModel>, val onEvent: (Event) -> Unit) : BaseModel
+
+  /** All events that [SwiftUiHomePresenter] can process. */
+  sealed interface Event {
+    /** Sent when `NavigationStack` has modified its stack. */
+    data class BackstackModificationEvent(val indicesBackstack: List<Int>) : Event
+  }
+}

recipes/recipesIosApp/recipesIosApp/ComposeContentView.swift

@@ -0,0 +1,63 @@
+//
+//  ContentView.swift
+//  recipesIosApp
+//
+//  Created by Wang, Jessalyn on 11/10/25.
+//
+
+import SwiftUI
+import RecipesApp
+
+struct ComposeView: UIViewControllerRepresentable {
+    private var rootScopeProvider: RootScopeProvider
+
+    init(rootScopeProvider: RootScopeProvider) {
+        self.rootScopeProvider = rootScopeProvider
+    }
+
+    func makeUIViewController(context: Context) -> UIViewController {
+        MainViewControllerKt.mainViewController(rootScopeProvider: rootScopeProvider)
+    }
+
+    func updateUIViewController(_ uiViewController: UIViewController, context: Context) {}
+}
+
+struct ContentView: View {
+    var appDelegate: AppDelegate
+    
+    @State var showComposeRecipes = false
+    @State var showSwiftUIRecipe = false
+
+    init(appDelegate: AppDelegate) {
+        self.appDelegate = appDelegate
+    }
+
+    var body: some View {
+        VStack {
+            Spacer()
+            
+            Button(action: { showComposeRecipes.toggle() }) {
+                Text("CMP-rendered recipes")
+            }
+            .buttonStyle(.borderedProminent)
+            
+            Spacer()
+            
+            Button(action: { showSwiftUIRecipe.toggle() }) {
+                Text("SwiftUI recipe")
+            }
+            .buttonStyle(.borderedProminent)
+            
+            Spacer()
+        }
+        .sheet(isPresented: $showComposeRecipes) {
+            ComposeView(rootScopeProvider: appDelegate)
+                .ignoresSafeArea(.keyboard) // Compose has its own keyboard handler
+        }
+        .sheet(isPresented: $showSwiftUIRecipe) {
+            SwiftUiRootPresenterView(
+                homePresenter: SwiftUiHomePresenterBuilder(appDelegate: appDelegate).makeHomePresenter()
+            )
+        }
+    }
+}

recipes/recipesIosApp/recipesIosApp/ContentView.swift

@@ -0,0 +1,119 @@
+//
+//  AppPlatform+Extensions.swift
+//  recipesIosApp
+//
+//  Created by Wang, Jessalyn on 11/24/25.
+//
+
+import RecipesApp
+import SwiftUI
+
+extension Presenter {
+    /// Returns an async sequence of type `Model` from a `Presenter` model `StateFlow`.
+    func viewModels<Model>(ofType type: Model.Type) -> AsyncThrowingStream<Model, Error> {
+        model
+            .values()
+            .compactMap { $0 as? Model }
+            .asAsyncThrowingStream()
+    }
+}
+
+enum KotlinFlowError {
+    case unexpectedValueInKotlinFlow(value: Any, expectedType: String)
+}
+
+extension Kotlinx_coroutines_coreFlow {
+
+    /// Returns an async sequence of Any? from the Kotlin Flow.
+    ///
+    /// The Flows send Any, so we lose type information and need to cast at runtime instead of getting a type-safe compile time check.
+    /// You can use `valuesOfType` instead which returns a stream that throws an error if the values are not of the right type.
+    /// `valuesOfType` is usually preferred because we want to catch bad values from Kotlin instead of the Flow going silent.
+    func values() -> AsyncThrowingStream<Any?, Error> {
+        let collector = Kotlinx_coroutines_coreFlowCollectorImpl<Any?>()
+        collect(collector: collector, completionHandler: collector.onComplete(_:))
+        return collector.values
+    }
+
+    /// Returns an async sequence from the Kotlin Flow.
+    ///
+    /// The Flows send Any, so we lose type information and need to cast at runtime instead of getting a type-safe compile time check.
+    /// If the Flow sends the right type, this stream will throw an error.
+    /// This is usually preferred because we want to catch bad values from Kotlin instead of the Flow going silent.
+    func valuesOfType<T>(_ type: T.Type = T.self) -> AsyncThrowingStream<T, Error> {
+        let collector = Kotlinx_coroutines_coreFlowCollectorImpl<T>()
+        Task { @MainActor in
+            do {
+                try await collect(collector: collector)
+                collector.onComplete(nil)
+            } catch {
+                collector.onComplete(error)
+            }
+        }
+        return collector.values
+    }
+}
+
+fileprivate class Kotlinx_coroutines_coreFlowCollectorImpl<Value>: Kotlinx_coroutines_coreFlowCollector {
+
+    let values: AsyncThrowingStream<Value, Error>
+    private let continuation: AsyncThrowingStream<Value, Error>.Continuation
+
+    init() {
+        let (values, continuation) = AsyncThrowingStream<Value, Error>.makeStream()
+        self.values = values
+        self.continuation = continuation
+    }
+
+    func emit(value: Any?) async throws {
+        if let castedValue = value as? Value {
+            continuation.yield(castedValue)
+        }
+    }
+
+    func onComplete(_ error: Error?) {
+        continuation.finish(throwing: error)
+    }
+
+    deinit {
+        print("Deiniting collector")
+    }
+}
+
+extension AsyncSequence {
+
+    func asAsyncThrowingStream() -> AsyncThrowingStream<Element, Error> {
+        if let self = self as? AsyncThrowingStream<Element, Error> {
+            return self
+        }
+        var asyncIterator = self.makeAsyncIterator()
+        return AsyncThrowingStream<Element, Error> {
+            try await asyncIterator.next()
+        }
+    }
+}
+
+extension Int {
+    /// Converts Swift Int to Kotlin's Int type for interop.
+    func toKotlinInt() -> KotlinInt {
+        return KotlinInt(integerLiteral: self)
+    }
+}
+
+extension BaseModel {
+    /// Gets the view for some `BaseModel`
+    ///
+    /// Returns. created by `makeViewRenderer()` if a model conforms to `PresenterViewModel` otherwise, crash the build for
+    /// debug builds or return a default view.
+    @MainActor func getViewRenderer() -> AnyView {
+        guard let viewModel = self as? (any PresenterViewModel) else {
+            assertionFailure("ViewModel \(self) does not conform to `PresenterViewModel`")
+            
+            // This is an implementation detail. If crashing is preferred even in production builds, `fatalError(..)`
+            // can be used instead
+            return AnyView(Text("Error, some ViewModel was not implemented!"))
+        }
+
+        return AnyView(viewModel.makeViewRenderer())
+    }
+}