[Similar Projects] MBL-2164: Add a Use Case object with stubs

Kickstarter.xcodeproj/project.pbxproj

@@ -3,7 +3,7 @@
 	archiveVersion = 1;
 	classes = {
 	};
-	objectVersion = 54;
+	objectVersion = 70;
 	objects = {
 
 /* Begin PBXBuildFile section */
@@ -3346,6 +3346,27 @@
 		E1FDB1E72AEAAC6100285F93 /* CombineTestObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CombineTestObserver.swift; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
+/* Begin PBXFileSystemSynchronizedBuildFileExceptionSet section */
+		AA5480D72D76B8B600EC2849 /* PBXFileSystemSynchronizedBuildFileExceptionSet */ = {
+			isa = PBXFileSystemSynchronizedBuildFileExceptionSet;
+			membershipExceptions = (
+				SimilarProjects/SimilarProjectsUseCaseTests.swift,
+			);
+			target = A755113B1C8642B3005355CF /* Library-iOS */;
+		};
+		AA5480D92D76B8B900EC2849 /* PBXFileSystemSynchronizedBuildFileExceptionSet */ = {
+			isa = PBXFileSystemSynchronizedBuildFileExceptionSet;
+			membershipExceptions = (
+				SimilarProjects/SimilarProjectsUseCaseTests.swift,
+			);
+			target = A75511441C8642B3005355CF /* Library-iOSTests */;
+		};
+/* End PBXFileSystemSynchronizedBuildFileExceptionSet section */
+
+/* Begin PBXFileSystemSynchronizedRootGroup section */
+		AA5480D22D76B8A400EC2849 /* UseCases */ = {isa = PBXFileSystemSynchronizedRootGroup; exceptions = (AA5480D72D76B8B600EC2849 /* PBXFileSystemSynchronizedBuildFileExceptionSet */, AA5480D92D76B8B900EC2849 /* PBXFileSystemSynchronizedBuildFileExceptionSet */, ); explicitFileTypes = {}; explicitFolders = (); path = UseCases; sourceTree = "<group>"; };
+/* End PBXFileSystemSynchronizedRootGroup section */
+
 /* Begin PBXFrameworksBuildPhase section */
 		A75511381C8642B3005355CF /* Frameworks */ = {
 			isa = PBXFrameworksBuildPhase;
@@ -6449,6 +6470,7 @@
 				D6B6F9BF20F403F400A295F7 /* UserAttribute.swift */,
 				1611EF6623B2752A0051CDCC /* UUIDType.swift */,
 				A734A2661D21A1790080BBD5 /* WKNavigationActionData.swift */,
+				AA5480D22D76B8A400EC2849 /* UseCases */,
 				A7C725851C85D36D005A016B /* DataSource */,
 				778F891A22D3E35600D095C5 /* Extensions */,
 				A73378F91D0AE33B00C91445 /* Styles */,
@@ -7387,6 +7409,9 @@
 			);
 			dependencies = (
 			);
+			fileSystemSynchronizedGroups = (
+				AA5480D22D76B8A400EC2849 /* UseCases */,
+			);
 			name = "Library-iOS";
 			packageProductDependencies = (
 				06634FC62807A4EB00950F60 /* Prelude_UIKit */,

Library/UseCases/SimilarProjects/SimilarProject.swift

@@ -0,0 +1,5 @@
+/// Represents a project that is similar to the currently viewed project.
+public protocol SimilarProject {
+  /// The identifier for the project.
+  var pid: String { get }
+}

Library/UseCases/SimilarProjects/SimilarProjectsState.swift

@@ -0,0 +1,14 @@
+/// Represents the various states of the similar projects presentation.
+public enum SimilarProjectsState {
+  /// The similar projects section is hidden from view.
+  case hidden
+
+  /// The similar projects are currently being loaded .
+  case loading
+
+  /// Similar projects have been successfully loaded.
+  case loaded(projects: [any SimilarProject])
+
+  /// An error occurred while loading similar projects.
+  case error(error: Error)
+}

Library/UseCases/SimilarProjects/SimilarProjectsUseCase.swift

@@ -0,0 +1,93 @@
+import Foundation
+import ReactiveSwift
+
+public protocol SimilarProjectsUseCaseType {
+  var inputs: SimilarProjectsUseCaseInputs { get }
+  var outputs: SimilarProjectsUseCaseOutputs { get }
+}
+
+public protocol SimilarProjectsUseCaseInputs {
+  /// Call when a user taps on a similar project.
+  /// Triggers navigation to the selected project's details.
+  ///
+  /// - Parameter project: The project that was tapped.
+  func projectTapped(project: any SimilarProject)
+
+  /// Call when a project ID is loaded or becomes available.
+  /// Initiates fetching of similar projects for the given project ID.
+  ///
+  /// - Parameter projectID: The ID of the project to find similar projects for.
+  func projectIDLoaded(projectID: String)
+}
+
+public protocol SimilarProjectsUseCaseOutputs {
+  /// The current state of similar projects.
+  var similarProjects: Property<SimilarProjectsState> { get }
+
+  /// Signal that emits when a user has tapped on a similar project.
+  /// Use this to navigate to the selected project's details.
+  var navigateToProject: Signal<any SimilarProject, Never> { get }
+}
+
+/// A Use Case for fetching similar projects and navigating to them when the user taps them.
+public final class SimilarProjectsUseCase: SimilarProjectsUseCaseType, SimilarProjectsUseCaseInputs,
+  SimilarProjectsUseCaseOutputs {
+  // MARK: - Initialization
+
+  init() {
+    self.navigateToProject = self.projectTappedSignal
+
+    self.projectIDLoadedSignal
+      .flatMap(.latest, self.fetchProjects(projectID:))
+      .observeForUI()
+      .observeValues { [weak self] state in
+        self?.similarProjectsProperty.value = state
+      }
+  }
+
+  // MARK: - Data loading
+
+  private func fetchProjects(projectID: String) -> SignalProducer<SimilarProjectsState, Never> {
+    // TODO: Implement this stub in MBL-2165
+    SignalProducer(value: projectID)
+      .delay(1.0, on: AppEnvironment.current.scheduler)
+      .map { _ in
+        .loaded(projects: [FakeProject(), FakeProject(), FakeProject(), FakeProject()])
+      }
+  }
+
+  // MARK: - Inputs
+
+  private let (projectTappedSignal, projectTappedObserver) = Signal<any SimilarProject, Never>.pipe()
+  public func projectTapped(project: any SimilarProject) {
+    self.projectTappedObserver.send(value: project)
+  }
+
+  private let (projectIDLoadedSignal, projectIDLoadedObserver) = Signal<String, Never>.pipe()
+  public func projectIDLoaded(projectID: String) {
+    self.projectIDLoadedObserver.send(value: projectID)
+  }
+
+  // MARK: - Outputs
+
+  public let navigateToProject: Signal<any SimilarProject, Never>
+
+  public let similarProjectsProperty = MutableProperty<SimilarProjectsState>(.loading)
+  public var similarProjects: Property<SimilarProjectsState> {
+    Property(self.similarProjectsProperty)
+  }
+
+  // MARK: - Type
+
+  public var inputs: any SimilarProjectsUseCaseInputs { return self }
+  public var outputs: any SimilarProjectsUseCaseOutputs { return self }
+}
+
+// MARK: - Supporting Types
+
+private struct FakeProject: SimilarProject {
+  let pid: String
+  init() {
+    self.pid = UUID().uuidString
+  }
+}

Library/UseCases/SimilarProjects/SimilarProjectsUseCaseTests.swift

@@ -0,0 +1,76 @@
+@testable import KsApi
+@testable import Library
+import ReactiveExtensions_TestHelpers
+import ReactiveSwift
+import XCTest
+
+final class SimilarProjectsUseCaseTests: TestCase {
+  private var useCase: SimilarProjectsUseCase!
+  private let projectTappedObserver = TestObserver<SimilarProject, Never>()
+  private let similarProjectsObserver = TestObserver<SimilarProjectsState, Never>()
+
+  override func setUp() {
+    super.setUp()
+    self.useCase = SimilarProjectsUseCase()
+    self.useCase.navigateToProject.observe(self.projectTappedObserver.observer)
+    self.useCase.similarProjects.producer.start(self.similarProjectsObserver.observer)
+  }
+
+  override func tearDown() {
+    self.useCase = nil
+    super.tearDown()
+  }
+
+  func testInitialState() {
+    // The useCase should start with a loading state
+    XCTAssertEqual(1, self.similarProjectsObserver.values.count)
+
+    if case .loading = self.similarProjectsObserver.values[0] {
+      // Expected loading state
+    } else {
+      XCTFail("Expected initial loading state")
+    }
+  }
+
+  func testProjectIDLoaded_emitsLoadedState() {
+    // When loading a project ID
+    self.useCase.projectIDLoaded(projectID: "project-123")
+
+    // Verify we're in loading state
+    XCTAssertEqual(1, self.similarProjectsObserver.values.count)
+    if case .loading = self.similarProjectsObserver.values[0] {
+      // Expected loading state
+    } else {
+      XCTFail("Expected loading state")
+    }
+
+    // Advance scheduler to simulate network delay
+    self.scheduler.advance(by: .seconds(2))
+
+    // Verify we received loaded state with projects
+    XCTAssertEqual(2, self.similarProjectsObserver.values.count)
+
+    if case let .loaded(projects) = similarProjectsObserver.values[1] {
+      XCTAssertEqual(4, projects.count, "Expected 4 similar projects")
+    } else {
+      XCTFail("Expected loaded state with projects")
+    }
+  }
+
+  func testProjectTapped_emitsNavigateToProject() {
+    // Create a fake project
+    let project = TestSimilarProject(pid: "project-456")
+
+    // Send project tapped event
+    self.useCase.projectTapped(project: project)
+
+    // Verify navigate signal fired
+    XCTAssertEqual(1, self.projectTappedObserver.values.count)
+    XCTAssertEqual("project-456", self.projectTappedObserver.values[0].pid)
+  }
+}
+
+// Test helper
+private struct TestSimilarProject: SimilarProject {
+  let pid: String
+}

Library/ViewModels/ProjectPageViewModel.swift

@@ -75,6 +75,9 @@ public protocol ProjectPageViewModelInputs {
 
   /// Call when right before orientation change on view
   func viewWillTransition()
+
+  /// Call when a similar project is tapped.
+  func similarProjectTapped(project: any SimilarProject)
 }
 
 public protocol ProjectPageViewModelOutputs {
@@ -161,6 +164,12 @@ public protocol ProjectPageViewModelOutputs {
 
   /// Emits when a block user request fails.
   var didBlockUserError: Signal<(), Never> { get }
+
+  /// The current state of similar projects.
+  var similarProjects: Property<SimilarProjectsState> { get }
+
+  /// Signal that emits when a user taps on a similar project.
+  var navigateToSimilarProject: Signal<any SimilarProject, Never> { get }
 }
 
 public protocol ProjectPageViewModelType {
@@ -743,6 +752,22 @@ public final class ProjectPageViewModel: ProjectPageViewModelType, ProjectPageVi
 
   public var inputs: ProjectPageViewModelInputs { return self }
   public var outputs: ProjectPageViewModelOutputs { return self }
+
+  // MARK: - Similar Projects
+
+  private let similarProjectsUseCase = SimilarProjectsUseCase()
+
+  public func similarProjectTapped(project: any SimilarProject) {
+    self.similarProjectsUseCase.projectTapped(project: project)
+  }
+
+  public var similarProjects: Property<SimilarProjectsState> {
+    self.similarProjectsUseCase.similarProjects
+  }
+
+  public var navigateToSimilarProject: Signal<any SimilarProject, Never> {
+    self.similarProjectsUseCase.navigateToProject
+  }
 }
 
 private func fetchProjectFriends(projectOrParam: Either<Project, Param>)