App/Sources/Enumerations/TodoGroup.swift

@@ -5,6 +5,16 @@ import SwiftUI
 ///
 /// This enumeration provides a semantic grouping mechanism for organizing and filtering todo tasks throughout the application.
 /// Each case represents a distinct category that helps users manage their tasks based on temporal relevance and completion state.
+///
+/// ## Features
+/// - Provides localized titles and icons for each group
+/// - Supports filtering of completed tasks within temporal groups
+/// - Enables color-coded visual categorization
+///
+/// ## Groups
+/// Groups are categorized into two types:
+/// - **Temporal groups** (`.today`, `.upcoming`, `.overdue`): Time-based categorization that can optionally include completed tasks
+/// - **Status group** (`.completed`): Contains all completed tasks regardless of due date
 enum TodoGroup {
     /// Tasks that have been marked as done, regardless of due date.
     case completed
@@ -20,6 +30,17 @@ enum TodoGroup {
 
 extension TodoGroup {
 
+    /// Indicates whether this group supports toggling the visibility of completed tasks.
+    ///
+    /// This property determines if a show/hide completed tasks action should be available for the group.
+    ///
+    /// - Returns: `true` for temporal groups (`.today`, `.upcoming`, `.overdue`) that can optionally
+    ///   show or hide completed tasks. Returns `false` for the `.completed` group since it exclusively
+    ///   displays completed tasks.
+    var canShowCompleted: Bool {
+        self != .completed
+    }
+
     /// The color associated with the task group.
     var color: Color {
         switch self {
@@ -40,7 +61,7 @@ extension TodoGroup {
         }
     }
 
-    /// The display title for the task group.
+    /// The localized display title for the task group.
     var title: LocalizedStringKey {
         switch self {
             case .completed: "enumeration.todo-group.title.completed"
@@ -57,6 +78,13 @@ extension TodoGroup {
 
 extension TodoGroup: CaseIterable {
 
+    /// All todo group cases in their display order.
+    ///
+    /// The cases are ordered by priority and temporal relevance:
+    /// 1. `.today` - Most immediate tasks
+    /// 2. `.upcoming` - Future tasks
+    /// 3. `.overdue` - Past due tasks requiring attention
+    /// 4. `.completed` - Finished tasks
     static var allCases: [TodoGroup] { [.today, .upcoming, .overdue, .completed] }
 
 }
@@ -65,6 +93,9 @@ extension TodoGroup: CaseIterable {
 
 extension TodoGroup: Identifiable {
 
+    /// The unique identifier for the group.
+    ///
+    /// Uses the case itself as the identifier, enabling use in SwiftUI's `ForEach` and other collection views.
     var id: Self { self }
 
 }

UnitTests/Tests/Enumerations/TodoGroupTests.swift

@@ -9,6 +9,25 @@ struct TodoGroupTests {
 
     // MARK: Computed tests
 
+    @Test(
+        "canShowCompleted returns correct values",
+        arguments: zip(
+            TodoGroup.allCases,
+            [true, true, true, false]
+        )
+    )
+    func canShowCompleted(
+        for group: TodoGroup,
+        expects expectation: Bool
+    ) {
+        // GIVEN
+        // WHEN
+        let canShowCompleted = group.canShowCompleted
+
+        // THEN
+        #expect(canShowCompleted == expectation)
+    }
+
     @Test(
         "group color match expected values",
         arguments: zip(