Todo repository protocol (#8)

This PR contains the work done to decouple the direct use of the `ModelContext` from `SwiftData` from the view model that uses it. In addition, the project transitioned to use Swift 6 and strict concurrency which brought some issues with the unit tests, so they were amended as well.

Reviewed-on: rock-n-code/todos-app#8
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

App/Sources/Extensions/ModelContext+Conformances.swift

@@ -0,0 +1,12 @@
+import SwiftData
+
+/// Extends ModelContext to conform to the TodoRepository protocol.
+///
+/// This extension allows ModelContext from SwiftData to be used as a todo repository,
+/// enabling dependency injection and facilitating unit testing by allowing mock
+/// repositories to be substituted during tests.
+///
+/// The ModelContext methods `delete(_:)` and `insert(_:)` already match the
+/// TodoRepository protocol requirements, so this extension simply declares conformance
+/// without requiring additional implementation.
+extension ModelContext: TodoRepository {}

App/Sources/Protocols/TodoRepository.swift

@@ -0,0 +1,28 @@
+import SwiftData
+
+/// A protocol defining the interface for a todo repository.
+///
+/// This protocol abstracts the underlying data persistence mechanism for todo tasks,
+/// allowing for dependency injection and easier testing. Implementations handle the
+/// storage and retrieval of Todo objects.
+protocol TodoRepository {
+
+    /// Deletes a todo task from the repository.
+    ///
+    /// This method removes the specified todo from persistent storage. The deletion
+    /// is typically performed immediately, though the actual persistence may be deferred
+    /// until a save operation occurs depending on the implementation.
+    ///
+    /// - Parameter todo: The todo task to delete from the repository.
+    func delete(_ todo: Todo)
+
+    /// Inserts a new todo task into the repository.
+    ///
+    /// This method adds a new todo to persistent storage. The todo is typically
+    /// tracked immediately, though the actual persistence may be deferred until a
+    /// save operation occurs depending on the implementation.
+    ///
+    /// - Parameter todo: The todo task to insert into the repository.
+    func insert(_ todo: Todo)
+
+}

App/Sources/View Models/NewTaskViewModel.swift

@@ -57,14 +57,14 @@ extension NewTaskView {
 
         // MARK: Functions
 
-        /// Saves a new todo task to the SwiftData model context.
+        /// Saves a new todo task to the repository.
         ///
-        /// This function creates a new `Todo` instance with the current property values and inserts it into the provided model context.
+        /// This function creates a new `Todo` instance with the current property values and inserts it into the provided repository.
         /// The title and note are trimmed of leading and trailing whitespace before saving.
         /// The `note` property value is only included if it's not empty after trimming.
         ///
-        /// - Parameter modelContext: The SwiftData model context to insert a new todo task.
-        func save(to modelContext: ModelContext) {
+        /// - Parameter repository: The repository to insert a new todo task.
+        func save(to repository: TodoRepository) {
             let trimmedTitle = title.trimmingCharacters(in: .whitespacesAndNewlines)
             let trimmedNote = note.trimmingCharacters(in: .whitespacesAndNewlines)
 
@@ -74,7 +74,7 @@ extension NewTaskView {
                 due: due
             )
 
-            modelContext.insert(todo)
+            repository.insert(todo)
         }
 
     }

App/Sources/View Models/TaskListViewModel.swift

@@ -87,21 +87,21 @@ extension TaskListView {
 
         /// Deletes tasks at the specified indices.
         ///
-        /// This method removes tasks from the model context after a swipe-to-delete action.
-        /// The deletion is performed through SwiftData's model context, which handles
+        /// This method removes tasks from the repository after a swipe-to-delete action.
+        /// The deletion is performed through the repository, which handles
         /// persistence and triggers automatic UI updates.
         ///
         /// - Parameters:
         ///   - tasks: The current array of tasks.
         ///   - offsets: The index set of tasks to delete.
-        ///   - modelContext: The SwiftData model context to perform the deletion.
-        func deleteTasks(
+        ///   - repository: The repository to perform the deletion.
+        func delete(
             _ tasks: [Todo],
             at offsets: IndexSet,
-            from modelContext: ModelContext
+            from repository: TodoRepository
         ) {
             for index in offsets {
-                modelContext.delete(tasks[index])
+                repository.delete(tasks[index])
             }
         }
 

App/Sources/Views/TaskListView.swift

@@ -45,7 +45,7 @@ struct TaskListView: View {
             group: viewModel.group,
             showCompleted: viewModel.showCompleted
         ) { tasks, offsets in
-            viewModel.deleteTasks(
+            viewModel.delete(
                 tasks,
                 at: offsets,
                 from: modelContext