Updated the TaskListView.Content view in the app target to support user reordering.

App/Sources/Views/TaskList/TaskListContent.swift

@@ -5,42 +5,82 @@ extension TaskListView {
 
     /// Internal content view that manages the dynamic SwiftData query for tasks.
     ///
-    /// This view is responsible for querying and displaying the list of tasks based on
+    /// This view is responsible for querying and displaying the list of tasks based on the specified
-    /// the specified group and completion status filter. It exists as a separate view
+    /// group and completion status filter. It exists as a separate view to enable dynamic query
-    /// to enable dynamic query updates when filter parameters change.
+    /// updates when filter parameters change.
+    ///
+    /// Task reordering is enabled based on the ``TodoGroup/canReorder`` property.
+    /// Groups that support reordering (``TodoGroup/today``, ``TodoGroup/upcoming``,
+    /// ``TodoGroup/overdue``) allow users to drag and drop tasks to change their order.
+    /// The ``TodoGroup/completed`` group does not support reordering as tasks are
+    /// displayed in chronological order by completion date.
     struct Content: View {
 
+        // MARK: Type aliases
+
+        /// Closure type for handling task reorder operations.
+        ///
+        /// - Parameters:
+        ///   - tasks: The current array of tasks.
+        ///   - source: The index set of items being moved.
+        ///   - destination: The destination index for the moved items.
+        typealias ReorderClosure = ([Todo], IndexSet, Int) -> Void
+
         // MARK: Properties
 
         /// Query to fetch todos filtered by group and completion status.
         ///
-        /// This query is initialized with a `FetchDescriptor` that applies predicates
+        /// This query is initialized with a todo fetch descriptor that applies predicates
         /// based on the group type and completion filter. SwiftData automatically
         /// monitors changes and updates the view when the underlying data changes.
+        ///
+        /// Tasks are sorted by their `order` property first, then by date-based criteria
+        /// specific to each group, enabling both manual and automatic ordering.
         @Query
         private var tasks: [Todo]
 
+        /// Indicates whether tasks in this view can be reordered through drag and drop.
+        ///
+        /// This value is derived from the ``TodoGroup/canReorder`` property and
+        /// determines whether the `.onMove` modifier is applied to the task list.
+        private let canReorder: Bool
+
+        /// Closure called when tasks are reordered through drag and drop.
+        ///
+        /// This closure is invoked by the `.onMove` modifier and is responsible for
+        /// updating the `order` property of affected tasks to reflect their new positions.
+        private let onReorder: ReorderClosure
+
         // MARK: Initializers
 
-        /// Creates a content view with a configured task query.
+        /// Creates a content view with a configured task query and reorder handler.
         ///
-        /// This initializer sets up the `@Query` with a fetch descriptor that filters
+        /// This initializer sets up a query with a fetch descriptor that filters
         /// tasks based on the specified group and completion status. When these parameters
         /// change, SwiftUI recreates the view with new values, causing the query to update.
         ///
+        /// The reordering capability is automatically determined based on the
+        /// ``TodoGroup/canReorder`` property. For groups that support reordering,
+        /// the provided closure will be called when users drag and drop tasks to new positions.
+        ///
         /// - Parameters:
         ///   - group: The todo group category to filter by (today, upcoming, overdue, or completed).
         ///   - showCompleted: Whether to include completed tasks in the results. Only applies to groups other than `.completed`.
+        ///   - onReorder: A closure called when tasks are reordered.
         init(
             group: TodoGroup,
-            showCompleted: Bool
+            showCompleted: Bool,
+            onReorder: @escaping ReorderClosure
         ) {
-            _tasks = .init(
+            self._tasks = .init(
                 FetchDescriptor<Todo>(
                     group: group,
                     showCompleted: showCompleted
                 )
             )
+
+            self.canReorder = group.canReorder
+            self.onReorder = onReorder
         }
 
         // MARK: Body
@@ -49,6 +89,12 @@ extension TaskListView {
         ///
         /// Displays either a content unavailable state or a list of tasks
         /// based on whether any tasks match the current filters.
+        ///
+        /// When tasks are present, displays them in a grouped list. The list supports
+        /// drag and drop reordering for groups where `canReorder` is true, allowing
+        /// users to manually prioritize tasks within the group. For groups where
+        /// reordering is disabled (such as completed tasks), the list is displayed
+        /// in read-only mode with chronological sorting.
         var body: some View {
             Group {
                 if tasks.isEmpty {
@@ -59,8 +105,18 @@ extension TaskListView {
                 }
                 else {
                     List {
-                        ForEach(tasks) { todo in
+                        if canReorder {
-                            TaskListView.Item(todo)
+                            ForEach(tasks) {
+                                TaskListView.Item($0)
+                            }
+                            .onMove { source, destination in
+                                onReorder(tasks, source, destination)
+                            }
+                        }
+                        else {
+                            ForEach(tasks) {
+                                TaskListView.Item($0)
+                            }
                         }
                     }
                     .listStyle(.grouped)
@@ -80,7 +136,9 @@ extension TaskListView {
     TaskListView.Content(
         group: .today,
         showCompleted: .random()
-    )
+    ) { _, _, _ in
+        // On reorder closure
+    }
 }
 
 #Preview(
@@ -90,7 +148,9 @@ extension TaskListView {
     TaskListView.Content(
         group: .today,
         showCompleted: false
-    )
+    ) { _, _, _ in
+        // On reorder closure
+    }
 }
 
 #Preview(
@@ -100,5 +160,19 @@ extension TaskListView {
     TaskListView.Content(
         group: .today,
         showCompleted: true
-    )
+    ) { _, _, _ in
+        // On reorder closure
+    }
+}
+
+#Preview(
+    "Task list content when only completed tasks shown",
+    traits: .sampleTasks
+) {
+    TaskListView.Content(
+        group: .completed,
+        showCompleted: .random()
+    ) { _, _, _ in
+        // On reorder closure
+    }
 }